THE DISTRIBUTION, ABUNDANCE,
AND FEEDING ECOLOGY OF
FOUR SPECIES OF FLATFISH
IN THE VICINITY OF
ELKHORN SLOUGH, CALIFORNIA
LIBRARY
MOSS LANDING MARINE LABORATORIES
P 0. Box 450
Moss Landing, California 95039
A Thesis
Presented to
the Faculty of the Department of Biology
San Jose State University
ln Partial Fulfillment
of the Requirements for the Degree
Master of Arts
By
David Anthony Ambrose
December, 1976
TABLE OF CONTENTS
Page
LIST OF TABLES • •
v
LIST OF FIGURES.
''
f
•
ACI<NOWLEDGEHENTS
•
• •
INTRODUCTION • •
•
•
xi
•
•
HATERIALS AND HETHODS.
•
Statistical Analysis Procedure.
.
.
• •
.
• •
•
•
Field and Laboratory Procedure.
RESULTS.
1
• •
• • •
5
•
5
•
•
Distribution and Abundance,
•
•
•
Horphological Relationships
•
16
•
• •
17
•
20
•
.
13
• • • •
...• .
Cumulative Prey Analysis.
vii
•
•
22
•
Variation of Diet with Size and Season. • • • • •
22
Feeding Frequency • • • • •
23
• • •
• • • • •
Feeding Habits·and Hajor Prey Groupings
Dietary Variations Be tHe en Localities •
Trophic Diversity
•
Dietary OverlaP
• •
Electivity,
DISCUSS ION
•
• • • • •
•
•
•
24
•
•
•
.
•
• •
Cumulative Prey Analysis.
•
41
•
•
•
•
•
Dietary Variation '"i th Size and Season.
Feeding Frequency .•
...
'
Feeding within a Location
iii
36
41
• • •
Distribution and Abundance.
Horphometric RelationshiPs.
33
35
• • • •
• • •
..
.
26
•
•
•
43
46
47
48
4g
Feeding Strategies • • .
.............
49 "
Flatfish Feeding Habits with Resoect to
. . . ...
.• ..
50
Troohic Diversity: Generalists vs. Specialists.
55
Dietary Overlap • •
58
Prey Natural History
•
•
Electivity. •
APPENDIX.
•
•
• •
•
59"
109
• • •
LITERATURE CITED. • • • • • • • • • • • • • • • • • •
iv
115
LIST OF TABLES
Table
1.
Page
Seasonal percent abundance and mean
number per otter trawl .tow of the
major flatfish species by locality. • • • •
2,
Fish collection locations, methods,
and times
3.
61
....... .....•
.
• • •
62
Mean ratios, X, and standard deviation
values, SD, for the standard length
to the length of the maxillary on
the ocular side • • , ••
4.
....
• •
•
63
..
64
Mean ratios, X, and standard deviation
values, SD, of the standard length and
stomach lengths to the length of the
entire gastrointestinal tract • • • • •
5.
Kendall tau rank correlation coefficients
of Index of Relative Importance values
of prey categories betHeen different
size classes within a flatfish species
by station and season
6.
....
• • • • •
65
Mean Kendall rank correlation of Index
of Relative Importance values of prey
categories among seasons by soecies • •
7.
66
Percent similarity indices for the combined
prey of all individuals of each flatfish
category between adjacent stations. • • •
v
67
8.
Percentage of unique prey categories
between adjacent localities by
flatfish grouping , • •
9,
10.
Trophic diversity summary,
..
• • • • • • •
• • • • • •
•
68
69
Index of ·overlap, __ CA• between flatfish
categories within a locality • • • • • • , •
vi
70
LIST OF FIGURES
Figure
Page
1.
Map of study area • • , • • • • •
2.
Length frequency histograms for
• • • • •
71
• • • • • •
73
, • • • • • • •
75
Platichthys stellatus by season
and locality. , , , • • • • •
3,
Length frequency histograms for
Parophrys vetulus by season
and locality. . . . . . • . .
4.
Length frequency histograms· for
Citharichthys stigmaeus
by season and locality. • • • • • • • • •
s.
Length frequency
histor~ams
77
for
Psettichthys melanostictus
by season and locality. • • • • • • • • •
6.
Linear
regression of the maxillary
length to the standard
by species • • • • • •
7.
79
length
o
•
o
••
• • • • •
81
Linear regression of the gastrointestinal
tract length to the standard length
by species. . . • . . . • . • • • • • • •
8.
83
Linear regression of the gastrointestinal
tract length to the stomach length
by species. • • • • • • • • • • • • • • •
9,
The cumulative number of prey categories
from the pooled number of fish for each
vii
85
flatfish category at the Kirby Park
and Dairy stations, • • • •
10.
•
•
•
• • • • •
0
87
The cumulative number of prey categories
from the pooled number of fish for
each flatfish category at the Bridge
and Ocean stations. • • • • • • • • • • • • •
11.
89
The numerical percent composition of the
major prey groupings for Platichthys
stellatus, Parophrys vetulus, and
Citharichthys stigmaeus by station. • • • • •
12.
91
Percent composition in.number (% N),
volume (% V), -and frequency of
occurrence (%
F.o.) of prey categories
with Index of Relative Importance values
~50 for Platichthys stellatus,
Parophrys vetulus, and Citharichthys
stigmaeus by station. • • • • • • • • • • • •
13.
93
Percent composition in number (% N);
volume:(% V), and frequency of
occurrence (% F,O,) of prey categories
with Index of Relative Importance
values ;;:.. 50 for Psettichthys
melanostictus at the Ocean station.
14.
•
0
•
•
•
Frequency histograms of individual
trophic diversity for Platichthys
stellatus, Parophrys vetulus, and
Citharichthvs stigmaeus by statron. • • • • •
viii
95
15,
Frequency histogram of individual
trophic diversity for Psettichthys
.....
99
the Kirby Park and Dairy stations, • , • , , ,
101
melanostictus at the Ocean station.
16,
The relationships
betl~een
the mean
evenness component (J) and the
mean richness component (H) of
individual trophic diversity
for each flatfish category at
17.
The relationships between the mean
. evenness component (J) and the .. mean
richness component (H) of individual
trophic diversity for each flatfish
category at the Bridge and Ocean stations, • • 103
18, .Diagram of the relative abundance
of the 10 most numerous items in the
environment as measured by benthic cores
(% P), the relative abundance of the
10 most numerous prey items in the diets
of each flatfish category
(% R), Electivity
(E), and the Percent Similarity Index value
(% SI) between the relative composition of
all items in the benthic cores and in the
diets of each flatfish category for Platichthys
stellatus, Paroohrys vetulus, and
Citharichthys stigmaeus at each station. , . . • 105
ix
19.
Diagram of the relative abundance
of the 10 most numerous items in the
environment as measured by benthic cores
-(% P), the
relative abundance of the 10
most numerous. prey items in the diets of
each flatfish category(% R), Electivity
(E), and the Percent Similarity Index
value (% Sl) between the relative composition
of all the· items in .the benthic cores and
in the diets of each flatfish category
for Psettichthys melanostictus at the
Ocean station. •
. . .. .
X
...........
101
ACKNOWLEDGEMENTS
I wish to express my sincere thanks to those who
generously contributed assistance and advice during
the course of this study.
Dr, Gregor Cailliet provided valuable guidance,
constructive criticism and encouragement during all
stages of the research and writing.
.All the members of
my master's committee have contributed valuable suggestions.
The field work could not have been accomplished
- -without·-many hours of capable-assistance ·by- Brooke Antrim
and many other.students at Moss Landing Marine Laboratories,
I am greatly indebted to Chris Jong, Peter Slattery, and
John Oliver for their expert identifications of many
invertebrate prey items and also for providing the benthic
invertebrate availability data,
This investigation Has
funded by a grant from the Pacific Gas and Electric
Company.
xi
INTRODUCTION
Estuaries and coastal embayments are extremely productive and have a major nursery function in that young
marine fish often aggregate in these bodies of water
(Orcutt, 1950; Ketchen, 1956: Gunter, 1957; Haertel and
Osterberg, 1967); therefore, they should be
studied more
intently. Man's activities·are increasing the stress on
these delicate environments, making it imperative that
more be learned about the ecological. processes involved
. in-order-to better evaluate .the_effects that man's. infringements are having on these unique·areas.
The fish fauna inhabiting Elkhorn Slough and the
Monterey Bay area have been well documented (Browning
~
al, 19721 Ku_kowski, 1972) and the majority of the
teleost fish inhabiting the slough are in the families
Engraulidae, Atherinidae, Embiotocidae, Gobiidae,
Cottidae, Bothidae, and Pleuronectidae.
The flatfish
(Bothidae and Pleuronectidae) were selected for this study
since they are abundant, easily captured (Allen, 1960) 1
and appear to form an important ecological assemblage
associated with the bottom.
The species investigated
starry flounder, Platichthys stellatus ~allas 181ij; English
sole, Parophrys vetulus Girard 1854; sand sole, Psettichthys melanostictus Girard 1854; and speckled sanddab,
Citharichthys stigmaeus Jordan and Gilbert 1882 -- have
been the subject of many previous papers ·and much is known
.1
2
about the life history of these species.
Starry flounders
are among the most abundant pleuronectid flatfishes from
Santa Barbara, California to Arctic Alaska and the Sea of
Japan in waters less than 275 m (Miller and Lea, 1972).
Males and females generally-become mature during their
secorid and third years respectively and spawn in shallow
water in Monterey Bay from November through February with
the peak season in December and January (Orcutt; 1950).
They are euryhaline and the young are known to occur in
rivers in salinities as low as .02 parts per thousand.
· - (Hubbs 1 -~ 1947 1 Haerte 1 ·and 0s terbet-g;c 1966), ":: The--feeding
habits -of: this species in Monterey Bay were qualitatively
described by Orcutt (1950).
Starry flounders appear to
feed primarily during the day (Miller, 1967),
English sole are also
very abundant pleuronectid
flatfish from San Cristobal Bay in Baja California, to
Unimak Island in western Alaska, between the
-about 550 m of water (Forrester, 1969),
surface and
Male and female
English sole mature in their second and third or fourth
years respectively (Ketchen, 1956) and the spawning period
in-Monterey Bay is similar to the January to March spaiYning
season in British Columbia (Taylor, 1946).
Spawning
grounds are usually in relatively sheltered water at a
depth of approximately 60 to 80 m where the bottom is soft
mud (Ketchen, 1956).
Sand sole are common pleuronectids in water less than
183 m over sandy bottoms from southern California to the
3
Bering Sea.(Hart, 1973).
The spawning period for these
fish is variable, since they have been reported to spawn
as early as January in Puget Sound (Smith, 1936) and as
late as July in Sydney Inlet (Manzer, 1947).
The feeding
.habits of adult sand sole in Puget Sound were investigated
by-Miller (1967).and he found that. this species is a
diurnal feeder •
.Speckled sanddabs are.·small bothids that are abundant
from.Magdalena Bay in Baja California to southern Alaska
(Miller and Lea, 1972).
Their.normal bathymetric range
··extends ·from a: depth of·-less .than ·.1- m-.to'-about. 90 m. ·.·This
-species .. is- probably the most abundant--demersal· fish inhabiting the shallow, sandy bottoms along the California coast.
Speckled sanddabs become ripe in their second year of life
and spawn in the· spring and summer months along the California
coast (Ford, 1965). Ford also found that these fish also feed
mainly during daylight hours.
The feeding behavior of'flatfish has long been a subject
of investigation (Bateson, 1890: Stevens, 1930; Bregnballe,
1961; Pearcy, 1962; de Groot, 1969; Olla, Wicklund and Wilk,
-1969; Frame, 1974; Levings, 1974); however, until this time,
no attempt has been made to deal with the trophic interactions
of young members of these four species in a quantitative,
ecological study.
Huch of the literature dealing with trophic
ecology has not concerned fish as subjects, but most of the
concepts discussed, such as trophic diversity or resource
breadth (Hurtubia, 1973) and food overlap (Horn, 1966), are
•
equally applicable to fish studies.
4
The objectives of this study Here to provide information
on the distribution, abundance, and feeding habits of the
four.major species of flatfish inhabiting Elkhorn Slough and
the shallow sandy shelf of Monterey Bay near the mouth of
the slough.
The relationships betHeen morphology, trophic
diversity, the degree of specialization, niche overlap, and
interspecific competition among these fish were investigated.
The feeding habits were also rela·ted to the availability of
prey organisms in the environment in an effort to obtain
information on the selectivity of feeding by each species.
l'fATERIALS AND METHODS
Field and Laboratory Procedures
Elkhorn Slough lies approximately halfway between
Monterey and Santa Cruz, California (Figure 1), and extends
inland approximately 4 kilometers (km), with an axial
len~th
of about 10 km.
The main channel-is approximately
10 meters (m) wide and has a depth of from 3 to 5 m
(Smith, 1973),
The drainage basin for Elkhorn
Slough is
only 585 km2 (W~ng, 1970).
Sampling was conducted at three stations witqin the
slough• Kirby Park, Dairy, and Bridge (Figure 1), and one
(the "Ocean") just outside the slough in Monterey Bay,
The Ocean sampling station was on the clean sandy
s~elf
on both sides of the entrance to the Hoss Landing Harbor
aporoximately 200 m offshore between depths of 5 to 10 m.
The Bridge station extended from the bridge at
High~.ray
1
approximately 1 km into the slough and was up to 5 m.deep.
The Dairy station was located 2 to 3 km into the slough
with a water depth of about 4 m,
The most inland station,
Kirby Park, extended from 5.5 to 6,5 km into the slough
~ere
the water was approximately 3 m deep.
The main sampling technique emoloyed in this study was
a small experimental otter_trawl (4.8 m head rope and 5,8 m
foot rope,-with 38.1 mm stretch mesh in the body and 31.7 mm
stretch mesh with a 12.7 mm stretch mesh liner in the codend),
The trawl was pulled approximately 37 m behind a Boston Whaler
6
equipoed with a 40 horseoower Johnson outboard motor. Tows
were made into the flow of the current at an estimated net
speed of 1 kilometer per hour.
Tows of five minute duration were made from August
through mid-December 1974.
The decrease in fish abundance
during the winter months necessitated lengthening the duration of the tows to 10 minutes so that a sufficient number
of fish could be obtained for gastrointestinal tract content
analysis.
The 10 minute towing period was maintained for
the remainder of the study (through October, 1975),
A large
. beach, seine. (approximately 80 m.. long. with 25,4-mrn_stretch
-mesh in the body and 12.7 mm stretch mesh in the purse) was
occasionally employed at each of the stations,
The number of fish taken during five minute tows was
doubled in order to standardize the results to a ten minute
towing period,
The percent abundance (% A) was calculated
as the percentage that a species composed of the total flatfish catch during a particular season at a particular station.
The mean number of flatfish per 10 minute tow (N/T) was calculated for each soecies at each season and station (Table 1).
Each station was sampled at least monthly (Table 2).
Stations with lower abundance often had to be sampled more
often in order to obtain an adequate number of fish for gut
content analysis.
Water temperature was taken before each
0
tow with a bucket thermometer accurate to + 0,5 C.
Salinity was measured by means of a Goldberg temperature
compensated refractometer accurate to
thousand.
z
0.5 parts per
The majority of the sampling was done between
7
0800 and 1600 hours and occurred at all tidal periods;
however, several tows with the
night.at various times
otte~
trawl were made at
of the year (Table 2),
The fish that were captured were measured to the
nearest mnL(standard length) and weighed to the nearest
0.1 gram (gm),
Live flatfish captured in excess of the
number required for gut content analysis were tagged with
Floy internal anchor spaghetti tags and released.
·remaining fish were preserved in
tation.was observed.
1~~
All the
formalin. No regurgi-
The body cavities of
these fish were
··injected· with· 10% ·formalin by. means 'of a· pressurized syringe
(Congdon ~
_ll• .1:975) 1 .
the gut contents.
in
order-. to ·ensure preservation of
In the case of large specimens, the entire
gastrointestinal tract and the gonads were removed and preserved in formalin.
After fixation, the·smaller fish and the
separated gastrointestinal tracts were
transferred to
5~~
soaked in water and
isopropyl alcohol before the gut contents
were analyzed.
The gut was surgically extracted by cutting at the esophagus and.at the rectum.
The connective tissue was removed
and the stomach length and total gastrointestinal tract
length was measured to the nearest millimeter,
The gastro-
intestinal tracts were cut longitudinally and with the contents intact, the fullness of the stomach was subjectively
scored ass 0= empty; 1= 25%; 2=
5~~;
3= 75%; and 4= 1007.
full (c.f. Tyler, 1970; DeWitt and Cailliet, 1972).
State
of digestion was scored as1 1= very finely digested, nothing
8
·recognizable·; 2= medium· digestion, some recognizable parts;
3= some digestion, some undigested material; and 4= undi·gested, whole animals (c.f, Tyler, 1970).
Prey organisms
were located, identified to the lowest possible taxon,
measured to
:t
0,1 1\lffi and counted using a Nikon dissecting
microscope equipped with an ocular micrometer.·· The contents
on each gut were considered, as unity, and the percent
volume contribution of each prey category was estimated by
eye (c.f.-McHugh, 1940; Bray and.Ebeling, 1975).
It was necessary to analyze the food material found
along the entire gastrointestinal- tract due to the varying
amounts of decomposition among the different·prey items.
In many cases, prey items of all cate~ories (polychaeta,
mollusca, and crustacea) could be identified even in the
posterior regions of the intestine. The undigestible material
ingested by these bottom feeding fish could be better estimated by examtning the entire gut length.
Sand sole and
speckled sanddabs appeared to digest the majority of their
food in their stomachs whereas in English. sole and starry
flounders most of the digestion occurred in the intestine.
Thus it was decided that the most equitable estimates of
number and prey types eaten by all flatfish species would
be achieved by analysis of the entire gastrointestinal tract.
Fish were found with empty stomachs but their intestines were
relatively-full of prey in recognizable condition,
These
fish were definitely not starving and it would have been
misleading to classify them as having empty stomachs.
9
The large number of prey categories in varying states
of decomposition and the large amounts of inorganic. debrisconsumed by some of the flatfish while feeding made any
gravimetric or displacement estimates of prey category
volume impractical.
Since only one person assigned.all the
estimates of prey volume, the subjective bias inherent in
this method was at least consistent.
The problems
'~ith
this
procedure were further minimized by having a large number of
estimates over a long time period.
·· The prey .were often fragmented, so counts had to be
standardized.
Each bivalve siphon was counted as an indi-
vidual (c.f. Bregnballe, 1961) and bivalve shells were counted
by attached hinges.
by the heads.
Polychaetes and crustaceans were counted
This standardization probably resulted in a
rather conservative estimate of the actual number of prey.
Voucher specimens of the prey items from each fish
'~ere
placed in a vial or jar and labeled inside and out with the
code for the station, collection number, and number.for the
individual fish, to be used for future reference if needed.
Food items about which initial identification was uncertain
were placed in
separ~tely
labeled containers for identifi-
cation by experienced invertebrate t_axonomists,
A_random sample of the fish from each station and season
was retained for further morphometric analysis_of the size,
position, and shape of teeth; the number, size and shape of
the gill rakers; and the size of the maxillary in relation to
-the standard length of the fish.
10
Since different size classes of many species of fish
have been shown to feed on different types of prey (Allen,
1942; Orcutt, 1950; Frame, 1974; Levings, 1974), the starry
flounders (Platichthvs stellatus) were separated into three
size classes for analysis of feeding habits: small (fish less
than or -equal to.'99 mm sta.ndal'd length), medium (100 :. ·199
A fe'~ individuals larger than
mm), and large ( 200 - 299 rnm),
300 mm were included in the 200- 299 mm category at the Ocean
station due to the low
abundance of
this species and the
l!;eneral··absence of· smaller starry flounders at that station.
These size classes were selected-on the basis of the roughly
quantitative study. by Orcutt (1950)·,-· which suggested that
these groupings ·might have d:lfferent·•feeding habits. ·The
speckled sanddab (Githarichthvs stigmaeus) were divided up
into two size classes: small (fish less than or equal to 79
mm in standard length) and large (those-80 mm or greater).
These size categories were chosen because Ford (1965)
suggested that adults might eat some,vhat different foods
than did juveniles,
The English sole (Paroohrys vetulus)
were similarly divided at 80 mm.
in order to better compare the
Th:ls division was selected
feedi~g
habits between the
same size groupings of English sole and speckled sanddabs.
The sand sole (Psettichthys melanostictus) were separated
into·~
150 mm and
> 150
mm s:lze ~>;roupings for-dietary
analysis.
For the purposes of statistical analysis the data from
the trawl collections and the gut content
examina~ions
were
11
grouped seasonally (November-January, February-April, MayJuly, and August-October).
because they corresponded
These groupings were chosen
\~ell
with the changes in abundance
and distribution patterns of the fish species, and·since
these groupings roughly approximated the normal·climatic
seasonality of the study area.
The August-October 1974 and
August-October 1975 seasons demonstrated similar patterns
in the distribution and feeding habits of the fish;· therefore,
fish from this season in both years were combined.
In.order tO'determine if the number of gastrointestinal
•
·-tracts-~examinedo·was
sufficient--to--represent the---majority· of
prey categories that \vere available to the fish in the
. environment, the gut contents from each fish category at
each station were randomly pooled and plotted against the
cumulative number of prey categories.
To compare the feeding habits of the flatfish in a
general manner, the prey were divided up into 16 major
groupingsz echiuroidea, polychaeta, miscellaneous annelida,
copepoda, gammaridea, caprellidea, mysidacea, miscellaneous
crustacea, bivalve siphons
·bivalvia, decapoda,
cellaneous.
>
10 mm, bivalve siphons£:. 10 mm,
ostracoda, gastropoda,.fish, and mis-
The numerical percent composition of each major
prey grouping was calculated for all flatfish in each size
category at each station,
The prey availability data for the slough were taken
from benthic cores that were taken at all stations along
30 m transects at approximately the -0.5 tide level (Nybakken,
12
1976). _-_The mean number of organisms per core at the Bridge
station was based upon 52 stanpard size cores (height= 17 em;
area= ,018 m2) taken at approximately bimonthly intervals
from July 1974 through August 1975.
The mean number of
individuals per core at the Dairy station was derived from
12 standard.size cores taken
1975,
in August 1975 and November
The Kirby Park station had large amounts of organic
debris which necessitated the use of smaller sized cores
(height= 17 c~, area=
,OOS m2),
The mean number of prey
items .per--core- from this station was based on data. from 49
-_7e·small--size-.-cores _-,taken· at-approxima tely~b-imonthly- -int:e~vals
from
July~l974--ehrough
August 1975.
The prey availability data for the Ocean station-were
derived from the mean number·of individuals per core for the25- most--numerous species based up(m 278 standard sized cores
made at depths from 9-18 m from June 1971 through June 1975
(Oliver~ al, 1976).
l3
Statistical Analysis Procedure
'The· Index of Relative Importance (IRI) of each prey
·category was calculated for food-containing fish as a·
combination of its numerical and volumetric importance
and frequency of occurrence (c,f. Pinkas
~
al, 1971),
The numerical importance ·(%N) of a particular item was
the percentage ratio of its abundance to the total abundance of all'items in the contents,
The volumetric im-
portance (%V)-was its average percent estimated volume,
The percent frequency of occurrence was the percentage of
'
·. f-ish-ocontaining at -least- one- individual .. of a. par.ticular
-·prey category.
The IRI was calculated-by summing the
numerical and volumetric percentage values and multiplying
by the percentage frequency of occurrence:
IRI
= (%N
+ %V) %FO
The Kendall coefficient of rank correlation,
tau,
(Kendall, 1962) was employed to compare the .ranks of IRI
values for prey of different size classes of fish within a
species,
The means of tau values of prey category rankings
.for the various flatfish groupings between seasons within
a locality were also calculated,
The Brillouin equation for diversity (H) was used to
measure the trophic diversity found in individual fish of
the various flatfish categories:
where N is the total number of prey individuals and N1 is
the number of individuals in the 1th prey category
(Brillouin, 1960),
The
contents of each gut were treated
14
as a finite collection because the patchiness of available
prey and the
feeding selectivity of the fish made it im-
. possible to obtain random samples of the available prey
population (Hurtubia, 1973).
The evenness component of diversity (J), .which measures
total numbers of prey individuals (N) distributed among the
prey categories (S), was calculated• J
= H/Hmax
*
where
and r = N-S
(Pielou, 1966),
The Percent Similarity Index, %SI (Silver, 1975), was
calculated· in an effort to.measure:the similarity-of,prey
types for a species of fish between adjacent stations and
to describe the
re~ationships
between the proportion by
number that all prey categories composed, both in the diet
of the fish and in the environment.
the sum
~f
This index was simply
the smaller value of the pair of proportions in
a comparison of two arrays of prey categories.
A value of
zero indicates no similarity and a value of 100 indicates
perfect agreement.
The percentage of unique prey categories
between adjacent localities was also calculated and considered to be high i f
L. 35% and low
if
< 35%.
The trophic overlap measure of Horisita (1959) as
modified by Horn (1966) was employed to show the overlap
in exploitation of alternative food sources from within the
same locality
15
where Pix was the proportion that the ith prey category
composed of the sum of the IRI values for fish grouping x
and Piy was the proportion that the ith prey category
composed of the sum of the IRI values for fish grouping y.
The overlap coefficient,
C),
,
varies from 0 when the samples
are completely distinct.(containing no food categories in
common) to 1 when the samples are identical with respect to
proportional importance of food.category composition.
The
index of dietary overlap values were divided up into three
categories for the purpose of analysisz high,
Cx
>.70;
·-.intermediate; _C_>.=:::_.10; and lm-r,_C.>.< .10.
The relationships between c.the -availability of the prey
in the environment and the proportions of the types of prey
in the fish's diet were expressed using the Electivity
Index, E (Ivlev, 1961).
E
=
(Ri-Pi)/(Ri+Pi)
where Ri or 1-R was the relative content of any ingredient
in the ration of the fish expressed .as a percent by number
of the individuals in that particular prey category to the
total number of individual prey items.
Pi or %P was the
relative value of the same ingredient in the food complex
of the environment as measured by the proport.ion of the
total mean number of organisms per core,
Electivity values
range from +1 to -1, with positive values indicating preference and negative values indicating "avoidance"·.
A value
of zero means that the item t-ras consumed in exact proportion
to its relative abundance in the prey community,
RESULTS
During the course of this study, 146 otter tra,•l and
7 beach seine samples, made from August 1974 through
October 1975 resulted in the capture of 369 Platichthys
stellatus (starry flounder), 655 Paroohrys vetulus (English
sole), 692 Citharichthys stigmaeus (speckled sanddab), and
75 Psettichthys melanostictus (sand sole).
A detailed description of the study area was provided
from a SCUBA diving survey of the slough from May to June,
--
1975 (Nybakken et al, 1976) and sediment size frequency
analysis at each station in February, 1976 (J• Oakden,
unpubl. .data).
The bottom at the Bridge station. was- com-
posed of muddy sand (mean grain size 2,35 microns), shells,
rocks and broken pilings.
At the Dairy station the bottom
was softer silty clay (mean particle size 1.81 microns)
with many shell fragments in the sediment.
The bottom at
the Kirby Park station was deeP, soft mud (mean-partic.le
size 0,36 microns) with hard debris such as rocks and
cement blocks scattered about.
Water turbidity was always
high at Kirby Park; visibility usually being much less
than 1,0 m (secchi disc).
Visibility varied considerably
with the season and the stage of the tide at the other two
slough stations; but the secchi"disc measurement usually
ranged between 1,5 and 4.5 m (Nybakken
~
al, 1976).
water throughout the year was generally clearer at the
Ocean station than it was in the slough.
16
The
17
Distribution and Abundance
Definite seasonal patterns were apparent in the distribution of the several species of flatfish (Table 1).
In
general, the abundance of Platichthys stellatus (starry
flounder) did not change very much throughout the year
within a locality,
Starry flounders were abundant at the
most inland station, Kirby Park, throughout the year and
they numerically dominated the catch at this station in
every season except May;_July.
The starry flounders '"ere
less abundant jat the Dairy station: however, they were still
.the
mos~
abundant flatfish taken at the Dairy in the November-
January and February-April seasons.
The number of starry
flounders taken per tow at the Bridge station was higher
than at any other station throughout the year, but the other
species of flatfish were also more abundant there and the
starry flounders were never the most abundant flatfish at
this station at any season during this study.
Fewer-.e starry
flounders were caught per tow at the Ocean than at any other
locality in all seasons and this species never was the most
abundant flatfish taken at this station in any season.
Parophrys vetulus (English sole) demonstrated the most
dramatic seasonality in distribution of all the flatfish
studied (Table 1). _ English sole were not taken from a:ny
locality during the November-January season,
Their numbers
increased steadily at all stations during the February-April
season and by the Hay-July season they were the most abundant
flatfish caught at every station except the Bridge,
In Hay-
18
July,--the English sole were particularly numerous at Kirby
Park.
The tendency -for English sole --to be concentrated in
the inland portions of the slough during the May-July season
was dramatically reversed in the August-October -season when
the majority of these fish were collected at the more seaward locations in the_ slough.
There were no English sole
taken in any of the 12 otter trawls made during the AugustOctober season at Kirby Park in two --consecutive years, and
fewer•-' English sole were taken per tow at the Ocean station
than from any other slough-locality for eachseason.
--The--most striking--feature of--'-the -distribution,_of
Ci:tharichthys _stigmaeus (speckled __ sandda:b) was their virtual
absence in all seasons from the most inland station, Kirby
Park (Table 1),
They w-ere also not very numerous at the
Dairy station with the exception of the August-October
season.
The center of abundance for this species was at the
Bridge station where it numerically-dominated the flatfish
catch in all seasons.
The number of sanddabs caught per tow
decreased at the Ocean station from what it was at the Bridge
station; however, this species was still one of the most
--abundant - flatfish caught at the Ocean station throughout
the year.
Psettichthys melanostictus (sand sole) were caught
exclusively at the Ocean station, never having been taken
in any of the 99 otter trawls or 5 beach seine sets made
in the slough.
The largest number of sand sole per tot>
were taken during the August-October season and the fetvest
19
during November-January (Table 1). In. the February-April
and May-July seasons, the catch tvas stable at about 1. 2
sandsole per
ten-~inute
tow,
rhis species made up the
largest percentage of the flatfish catch only during the
August-October season.
--The distribution of the starry flounders varied .with
the size of the fish (Figure 2). Starry flounders less than
80 rom were taken-infrequently and only from Kirby Park and
starry flounders less than 200 rom in
standa~d
also concentrated-at this locality.
The mean standard
length were
lengths ..:of "this species were· significantlycsma:tler -(t-test,
p= <.001) -at ·Kirby Park than at any of the other stations
throughout the year.
The majority of the starry flounders
caught at the other slough stations were about 235 rom and
still immature, probably in their first and second years
(Orcutt, 1950),
Mature flounders , greater than 300 rom
(Orcutt, 1950)i were most often captured at the Bridge
station,
The average sizes of the starry flounders taken
at the Ocean and Bridge stations ''ere similar; however, the
Ocean station had fewer starry flounders shorter than 200 rom
standard length.
English
sole utilized the slough from February through
October, during the first year of their lives (Smith and
Nitsos, 1969) •.. They. appeared to
concentrate in the most
inland portions of the slough during the Hay-July season
when their average size was about 76 mm (Figure 3).
Very
few Englis-h sole larger than 100 mm were ever taken at Kirby
20
Park.
In the August-October season,·the average size of
this species was about 102 mm and they were concentrated
in· the most seaward regions of the slough, ·while none were
taken at Kirby Park.
No English sole larger than 140 mm were
ever caught in the slough.
English s.ole larger than 250 rom
were takenat the Ocean station during the February-April
and August-October seasons.
The size frequency distribution of the speckled sanddabs
did not change very.much during the year at any station
(Figure 4).
Immature fish,.less than about 78 mm in standard
~-1-Emgth--(-Ford ,---1965),
·composed t:he--majority-of- -the catch- at
the.Dairy.and Bridge stations. _Larger, more mature fish.were
more frequently caught at the Ocean station,
Sand sole were taken at the Ocean station throughout the
year (Figure 5).
Recently metamorphosed individuals '~ere
caught early in the August-October season.
The majority of
the sand sole caught were less than 250 mm and immature
(Manzer, 194 7) ,
Morphological Relationships
A comparison of the morphological relationships among
the flatfish revealed that each species was variously adapted
·to exploit different food resources.
The ratio of standard
length to length of ocular side maxillary was significantly
unique (t-test, p =<.001) among all species of flatfish
(Table 3),
The 26 sand sole measured had proportionately
21
the- largest-mouths, with the 32 speckled sanddabs being
second largest,
The measurements of the 26 English sole
-and 25-starry flounders indicated their mouths were smaller
proportionately than. those of the starry flounders,
The
sizes of the mouths of the starry flounders and English sole
were closer to each other than to either of the other t\-10
flatfish species,
Gastrointestinal tract length also varied significantly
(t-test, p=_.<.OOl) -between each-pair of the flatfish studied
(Table- 4),
-The starry flounders had by far the longest
gastrointestinal tract, __ equalling about 13cr/. of the standard
length.
-The English sole and speckled sanddabs had. inter-
mediate gastrointestinal tract lengths, respectively 94% and
86% of their standard lengths,
The sand sole had the shortest
gut, equal to only 75% of the standard length,
Stomach length as a proportion of total gastrointestinal
tract length was also significantly different (t-test, p= .001)
for each of the flatfish species (Table 4).
The length of
the stomach in all of the flatfish was inversely correlated
with the length of the gastrointestinal tract, that is, those
fish that had the longest gastrointestinal tract had proportionately the smallest stomach and vice versa,
_ The least squares linear regression and correlation
coefficients for the relationships between the maxillary
length and standard length (Figure 6), the gastrointestinal
tract length and standard length (Figure 7), and the gastrointestinal tract length to stomach length (Figure 8) demon-
22
strated that in all species the morphological relationships
were strongly linearly correlated.
Cumulative Prey Analysis
The-leveling off of the number of cumulative prey
categories for all the species and size groupings of flatfish taken from the slough stations, with the exception of
the .starry flounders.599 nun at Kirby Park (Figures· 9 and 10)
indicated that the majority of the utilizable prey categories
'"ere adequately sampled by the number of fish guts examined.
The Ocean station's potentially.utilizable prey were probably
not sufficiently well represented for the English sole, the
large starry flounder, and the sand sole
> 150
nun.
A suf-
ficiently large number of these fish was sampled 1 hmvever 1
to demonstrate the feeding relationships among the flatfish
caught at-this station.
In
general, the number of potential
prey categories utilized by the fish increased from Kirby
Park to the ocean and the number of fish guts that were required to give a good estimate of all the types of prey eaten
also increased in the same manner.
Variation of Diet with Size and Season
The Kendall rank correlation comparison of prey Index
of Relative Importance values demonstrated that dietary
changes with size were more pronounced in some of the flatfish
than in others (Table 5)
1
and that there was no significant
23
change in the relative importance of the prey categories
for any of the fish groupings at any location throughout
the year (Table 6).
The starry flounder size classes 100-
199 mm and 200-299 mm and the sand sole ~ 150 mm and
> 150
mm were the only flatfish species to have prey rankings which
were. clearly different at the .05 probability level,
~
The
99 mm size class and the 100-199 mm size class starry
flounders were only marginally similar at the ,OS level;
therefore, they were also separted for feeding habit analysis.
The diets of the English sole and the speckled sanddabs did
not change significantly. as ·-the -fi-sh grew, so. all- size classes
of these two-species were ·lumped together in_the feeding
habit study.
Feeding Frequency
There were few empty gastrointestinal tracts for any of
the species throughout the year.
Six percent of the 272
starry flounders' guts were empty and 5 percent of the 357
speckled sanddabs' gastrointestinal tracts were empty.
1% of the 259 English sole and
examined were empty,
~k
Only
of the sand sole's guts
The only large difference in the per-
centages of empty guts bet,veen localities was that for the
speckled sanddabsz 1%-of the 245 fish taken from the slough
stations had empty gastrointestinal tracts, while 14% of the
113 fish from the Ocean station had empty gastrointestinal
tracts,
There were, however, differences in the fullness and
24
amount of digestion of the food among the flatfish categories.
The small and medium-sized starry flounders,
English sole and speckled sanddabs taken during the day
aooear to feed continually on small prey since
8~h
of the
743 guts of these species examined were half full and had
a state of digestion of 3 or higher indicating recently
eaten prey,
The large starry flounders and the sand sole
seem to feed more sporadically since only 21% of the 163
guts examined were more than half full and contained recently eaten prey.
Feeding Habits and Major Prey .Groupings
Distinct trends were recognizable in the feeding habits
of the various flatfish categories when the numerical percent composition of the major prey categories were analyzed
(Figure ·11),
Small starry flounders ( <99 mm) were captured
in limited numbers and only from the Kirby Park station.
Polychaetes composed over half of the diet by number
(53.~h).
Small bivalve siphons less than 10 mm in length and 3 mm in
diameter were numerically next important (23,6%),
Gammarid
amphipods composed about 10.4% of the prey,
The medium sized starry flounders (100-199 mm) also were
.more common at the inland portions of the slough where. polvchaetes were of less importance for this size class than for
the smaller sized starry flounders (Figure 11).
Whole bi-
valves and the small bivalve siphons increased in numerical
importance.
Gammarid amphipods, particularly at Kirby Park,
25
composed a larger portion of the diet of the 100-199 mm
P. stellatus (23.5%) than they did for the ~99 mm size class.
Large starry flounders (200-299 mm) had the center of
their distribution at the seaward stations of the slough and
offshore.
Polychaetes were less important in the diet of
the large starry flounders than they were in the diet of the
medium-sized starry flounders (Figure 11).
Large bivalve
s i?hons longer than 10 tnm and wider. than about 3 mm became
important in the diet and the smaller siphons were numerically insignificant for the large starry flounders.
Whole
bivalves continued to increase in numerical importance as
the starry flounders grew.
Echiuroids were a numerically
important food source, particularly at the Bridge station.
Crabs increased in importance for the large starry flounders
particularly at the Ocean station.
Gammarid amphipods were
not numerically significant in the diets of large starry
flounders.
Parophrys vetulus (English sole) were seasonal inhabitants
of various areas of the slough and at times utilized the
entire slough.
Similar to the medium-sized starry flounders,
English sole preyed upon annelids, whole bivalves and small
bivalve siphons to a large degree (Figure 11),
Crustaceans
other than decapods were generally more numerically important
to the English sole than they were to the starry flounders.
Decapods were not an important food source for the English
sole.
Ostracods were somewhat numerically important at the
Ocean station.
26
Citharichthys stigmaeus (speckled sanddabs) utilized
onlY the seaward stations of the slough and the most important prey grouoing for the speckled sanddabs normally were
t:he crustaceans, particularly - amphipods and mysids (Figure
11).
Polychaetes were numerically most important to the
sanddabs only at the Bridge station.
When this species fed
in the slough, the small bivalve siphons were also consumed.
Whole bivalves were
n~numerically
important in the diet of
speckled sanddabs, ·oecapods and to a lesser extent fish
were also eaten.
Like the English sole, the speckled sand-
dabs also fed to some extent on ostracods at·-,the Ocean ·station.
The numerical importance of the major prey groupings for
Psettichthys melanostictus (sand sole) was not graphically
presented due to the extreme trophic specialization demonstrated by this species.
Fish composed numerically 62% of
the diet of the large sand sole (
>150
mm in standard length).
The only other numerically important major prey grouping was
the decapod crustaceans (19.8%).
Mysidacea was the only
imoortant major prey grouping for the small sand sole
(~150 mm), comprising numerically 86,4% of the diet.
Dietary Variation Between Localities
The relationshio between the percent number, percent
volume, and percent frequency of occurrence of the prey
categories with Index of Relative Importance (IRI) values
greater than or equal to SO for each flatfish category at
each station helped to demonstrate the differencesand
27
similarities of the feeding habits of the flatfish among
the different localities (Fi~1res 12 and 13),
The number
oi fish guts examined which contained food, the numerical
values for the
percent number, percent volume, percent
frequency of occurrence, and the ranking of the IRI values
for all prey categories by flatfish species are included for
each station in Appendix Tables B-E,
The flatfish taken at Kirby Park fed primarily on small
polychaetes, one species of amphtpod, and small bivalve
siphons (Figure 12).
The polychaete Streblospio benedicti
was the most important -identifiable prey category in the
diets of both the small starry flounders and the English
sole.
Another polychaete·, Capitella capitata, was an
important prey category for all the flatfish taken at Kirby
Park.
Gammarid amphipods of the genus Corophium were eaten
frequently and were dietarily important for all the flatfish
caught at this station, especially for both size classes of
~he
starry
flounders,
The cumacean Cyclasois sp. was fre-
quently important only in the diet of the English sole.
Small
bivalve siphons (probably Macoma spp.) had, excluding digested
material, the highest IRI rank for the medium-sized starry
flounders and the second highest ranks in the diets of both
the small starry flounders and the English sole.
Medium-
sized starry flounders were the only flatfish at Kirby Park
that fed importantly on whole bivalves.
Gemma gemma was the
pelecypod most frequently eaten by the flounders at this
station.
28
Starry flounders caught at the Dairy station revealed
changes in prey category importance when compared with the
flounders taken at Kirby Park (Figure 12),
A polychaete,
Armandia brevis, which was not important to the medium-sized
starry flounders at Kirby Park, was,· excluding digested
material, the second most important. prey category eaten by
these flatfish at the Dairy station.
Streblospio was eaten
.less frequently by these fish at the Dairy station than they
were at Kirby Park • . Another species of amphipod, Aoroides
columbiae, replaced Corophium spp. in the dietary importance
for the medium-sized starry flounders taken at the Dairy
station,
The small Macoma-Iike bivalve siphons·.were about
equally important to the medium-sized starry flounders at the
Dairy and Kirby Park stations.
Macoma spp. replaced Gemma
gemma as the most important whole bivalve fed upon by this
fish at the Dairy station,
Changes in the diet of the English sole taken at the
Dairy station and Kirby Park were similar in many respects
'to the changes noted for the medium-sized starry flounders
(Figure 12).
Streblospio was less important and_Armandia
was eaten more frequently by the English sole at the Dairy
station, compared to Kirby Park.
The dietary increase in
importance of Armandia from Kirby Park to the Dairy station
was not as great for the English sole as it was for the
medium-sized starry flounders.
Aoroides replaced Coroohium
as the most important amphipod at the Dairy station,
Macoma
spp. were consumed in low numbers but over 10 times more
29
frequently by the English sole taken from the Dairy station
than from Kirby Park.
The diets of the speckled sanddabs from the Dairy station
contained fewer prey categories with IRI values greater than
50 than did any other flatfish category taken at that station.
Aoroides was overwhelmingly the most important prey category
fed upon by the speckled sanddabs at this station (Figure 12)J
and was consumed in higher numbers, more frequently, and made
up a larger volumetric portion of the diet in the speckled
sanddabs than in the diets of any of the.other flatfish,
Juvenile mysids were eaten on only a··few occasions by the
sanddabs 1 ·but in sufficientlyclarge·numbers to be considered
dietarily important at the Dairy station,
Speckled sanddabs
consumed the small.Macoma-like bivalve siphons more frequently
than any other prey category,
but the numerical and volu-
metric importance was far less than for the amphipods,
There was not a large change in the ordering of the most
important prey items for.the medium-sized starry flounders
'
between the Dairy
and Bridge stations (Figure 12),
was
Armandia
even more important in the diets of these fish.at the
Bridge station than it was at the Dairy station,
Capitella
was dietarily important for the medium-sized starry flounders
at the Bridge station but not at the Dairy station, whereas
the opposite was true with Streblospio.
Aoroides was very
much less important to these fish at the Bridge station
than it was at the Dairy station.
The Macoma-like siphons
were also still very important for the medium-sized starry
flounders- at the Bridge locality,
-The
major change in the diet of the large starry floun-
ders between the Dairy and the Bridge stations was the complete dominance of the diet by Urechis caupo at the Bridge
relative to the insignificant role itplayed in their diet
at the Dairy station (Figure 12). ··Armandia was ·eaten infrequently but in large numbers at both stations.
The mud
crab, Hemigrapsis oregonensis, was also relatively important
in the diets of the large starry flounders at both the
Bridge and Dairy stations,
Tresus nuttallii siphons were.
··-much--mere important-to--the -large starry .f-lounders--at. the
Bridge station than at the
Dairy~station.
:_-Saxidomus
nuttallii siphons were numerically abundant for these
fish caught at Dairy station but not for the ones taken
at the Bridge station.
There were a few changes in the categories of prey
im~ortant
to the English sole between the Bridge and Dairy
stations. Armandia was much more important and Streblospio
was less important for these fish at the Bridge than the
Dairy station.
Another polychaete, Notomastus tenuis, was
imoortant in the diet of the English sole at the Bridge
station but not at the Dairy station,
Aoroides was eaten
at about the same frequency at both stations, but this
amphipod was consumed in lower numbers at the Bridge station.
The small Macoma-like bivalve siphons were still the most
dominant prey category for the English sole at the Bridge
station, although the siphons' numerical abundance was
31
somewhat decreased at this station with respect to the
Dairy· station,
_The change in the importance of prey categories for
the speckled sanddabs between the Bridge and Dairy stations
was very noticeable, but the sanddabs at the Bridge station
continued to have a fewer number of prey categories with
IRI values greater than 50 than did any other flatfish
category taken at this locality (Figure 12).
Armandia
was more important in number, volume, and frequency of
occurrence in the sanddabs taken at the Bridge than at
the. Dairy..station •..The ..opposite trend was noticed for
Streblospio 1 since it was very important in the-diets of
speckled sanddabs at the Dairy but not at the Bridge
station,
Aoroides was also very much less important for
these fish at the Bridge station,
Caprellid amphipods
were dietarily important only to the sanddabs at the
Bridge ·station.
The majority of the prey categories eaten by all the
flatfish at the Ocean station (Figures 12 and 13) were
different from the prey categories eaten by the flatfish
caught within the slough.
The large starry flounder and
the speckled sanddabs taken at the Ocean station had no
major prey categories in common with the same two species·
of fish captured at any other station in the slough.
The
starry flounders at the Ocean station ate mostly large
polychaetes (Nothria elegans), crabs (Pinnixa franciscana
and Cancer magister), whole bivalves (Siligua spp.), and
32
sand dollars.
The speckled sanddabs concentrated their
feeding on mysids (Acanthomysis davisii), amphipods
(Atylus tridens} and the pea crab (Scleroplax granulata).
The English sole taken at the Ocean station had consumed
only 3 major prey categories that were also. eaten by_these
fish at any station in the slough (Armandia, Capitella,
and small bivalve siphons).
The order of importance of
these 3 prey items was very different between the Ocean
and slough stations, English sole at the Ocean consumed
mostly the polychaetes (Prionospio pygmaeus, ~rmandia, and
Capitella),: the -amphipods (Synchelidum spp. and Monocu- ·
loides .spp.) , __ and c.the ostracod_ (Euphilomedes carcharodonta).
The sand sole were··caught only at the Ocean station and
there was no overlap in the major prey categories between
the sand sole and any of the flatfish caught in the slough.
Small sand sole consumed primarily the mysids (Acanthomysis
davisii, Metamysidopsis elongata and Neomysis kadiakensis)
and the shrimp (Crangon spp.) (Figure 13),
Large sand sole,
greater than 150 mm, ate more fish (Engraulis mordax and
Psettichthys melanostictus).
The Percent Similarity Index (%Sl) for the combined
prey of all individuals of each flatfish category between
adjacent stations (Table 7) indicated the following relationships• prey at the-Dairy and Bridge stations were most
similar, the Kirby Park and Dairy stations were nex-t, and
prey categories eaten by the flatfish at the Ocean and
Bridge stations were most dissimilar.
1
All the flatfish
33
had a high percentage of prey unique to Kirby Park (
> 35%)
and a low percentap,e of prey unique to the Dairy station
( < 35%)
when these two stations were compared.
Prey unique-
ness was high for the large starry flounders, the English
sole, and the speckled sanddabs at the Bridge station.and
low at the Dairy station.
The medium-sized starry flounders
were the exception to this trend, having a high percentage
of their prey unique Dairy station and a low number of their
orey unique to the Bridge station. All the flatfish taken at
the Bridge and Ocean stations had high percent unique prey
c<'ltegories at the Ocean station and a comparatively low
percent prey uniqueness at the Bridge station.
Trophic Diversity
·The distribution of the trophic diversity in individual
guts was somewhat skewed for several of the flatfish (Figures
14 and 15), but values of trophic diversity were similar to
the median values in almost all'cases (Table 9).
The
majority of the results of this analysis will be considered
from the mean individual trophic diversity standpoint.
The mean individual trophic diversity value (H) was
more variable among· the species than the mean evenness
comoonent of individual dietary diversity (}) (Figures 16
and 17).
H contributed more to the trophic diversitv
differences among the species than did J.
English sole had the highest H value of all flatfish
at all localities, ranging around .86 at the slough stations
34
and increasing to 1.00 at the Ocean station (Table 9).
J for this species was about .75 at Kirby Park and the
Dairy stations, but decreased to about ,64 at the Bridge
and Ocean stations.
Speckled sanddabs had the second highest trophic
diversity in individual guts at all localities where they
occurred.
The H value (,51) for the sanddabs at the Ocean
station should be higher than the value for the large
,:
.
starry flounders since the skewed distribution of the
trophic diversity values in the flounders made the H value
---misleadingly-high at -.53 -(Figure 14). --:The median value of
,38 was probably a better estimate of-the trophic diversity
for individual starry flounders at the Ocean station,
Sanddabs had their highest
H value
•
at the Bridge station
(,75), and their values at the Dairy and Ocean stations
were similar to each other at- .53 and ,51 respectively.
The evenness component of diversity for the diet of the
speckled sanddab increased progressively toward the Ocean
station (Table 9),
The medium-sized starry flounders (100-199 mm) had
one of the lowest overall individual trophic diversities
at all of the slough stations (Table 9).
H values for
this species decreased progressively away from Kirby Park.
The mean evenness component of diversity fluctuated between
,55 and .65 within the slough,
The large starry flounders also had H values which
were less than those of the English sole or speckled sand-
•
'
35
dabs at all locations,
values for
The individual trophic diversity
this species were essentially the same at all
localities: Dairy,
median H= ,38,
H=
,37; Bridge,
H=
,36; and Ocean,
The evenness in individual diets of large
starry flounders was higher at the slough stations than
it was at the Ocean station (Table 9),
Both size classes
of sand sole ( <150 mm and >150 mm) had H values which
were lower than any other flatfish from any locality and
J values which were among the highest of any of the flat-
fish (Table 9),
Dietary Overlap
The small starry flounders at Kirby Park had a high
value (
>. 70)
overlap value
C~
with the English sole and intermediate dietary
c;:::...1o)
with the medium-sized starry flounders
at this locality (Table 10).
The overlap between the diets
of the medium-sized starry flounders and the English sole
was high at all slough stations and increased progressively
from Kirby Park to the Bridge statio~.
Speckled sanddabs
had only intermediate values of overlap with all other
flatfish categories at the Dairy station, but at the Bridge
locality the overlap of the sanddabs with the English sole
and medium-sized starry flounders almost doubled resulting
in high CA values.
The diets of the large starry flounders
showed very little overlap (CA =S.10) with any other flatfish at every locality where they were taken,
The only
significant overlap between any of the flatfish at the Ocean
36
station was between the speckled sanddabs and the small
sand sole.
to
the_lar~e
This high overlap was due almost exclusi'Tely
extent both of these fish fed upon one species
of mysid, Acanthomysis davisii.
Electivity
The results of Ivlev's Index of Electivity (E) and the
Percent Similarity Index (% SI) help to indicate whether
differences in the types of prey items eaten by the flatfish
at the various locations were due to preference or availabili~y.
Prey items such as bivalve siphons, large biYalves,
harnacticoid copepods, Urechis cauno, various species of
mysids, active amphipods, and large polychaetes were important in the diets of the flatfish but were not well represented in the benthic cores.
Organisms such as oligochaetes,
nhoronids, and nemertean worms that were very numerous in
the cores taken in the slough, and several species of amphinods and polychaetes that were numerically very imoortant in
the cores from the Ocean station were not found abundantly
in any of the flatfish (Figures 18 and 19),
The small starry
flounders, medium-sized starry flounders, and English sole
sampled the available prey in a more similar way to the
benthic cores than did the large starry flounders, speckled
sanddabs, or sand soles,
The benthic cores taken at Kirby Park caught Streblosoio
benedicti, Oligochaetes, Corophium spp., Cyclasnis sp., and
Gemma gemma in large numbers (Figure 18).
The small starry
I
37
flounders at this locality selected positively for
Streblosoio, Caoitella caoitata, and the small bivalve
siphons, while they fed upon the Oligochaetes, Corophium,
Cyclaspis, and Gemma in lesser prooortions than were taken
with the cores,
The medium-sized starry flounders showed a
preference for Capitella, small bivalve siphons and
'~hole
bivalves, but consumed Streblosoio, Oligochaetes, Coroohiurn,
Cyclaspis and Gemma in fewer numbers than weresampled with
the cores.
The English sole had positive electivity values
for Armandia brevis, Caoitella, harpacticoid copepods, and
:·small-bivalve--siphons. -English so-le -showed-no preference
for Streblosoio or.Exogone lourei, by feeding on them in the
same proportions as they were taken by the cores.
These fish
had negative electivity values for Oligochaetes, Coroohium,
Cyclaspis and Gemma, indicating avoidance.
The cores at the Dairy station were numerically dominated
by Oligochaetes
and Streblospio, and Capitella and Coroohium
were present in lesser numbers (Figure 18).
The medium-sized
starry flounders had positive E values for Armandia, unidentifiable polychaetes, Aoroides columbiae, bivalve siphons and
whole bivalves, Notomastus tenuis and Macoma nasuta had E
values close to zero, indicating feeding by this fish on
these prey in proportion to the prey's abundance in the cores.
The medium-sized starry flounders avoided Streblosoio,
Caoitella, Oligochaetes, and Coroohium at this station.
The large starry flounders selected positively for Armandia,
Urechis caupo, Hemigraosis oregonensis, and numerous types
38
of large bivalve siphons and 'mole bivalves,
of the
~prey.
The majority
items .taken by the cores at this station '"ere
avoided by these fish.
The English sole had positive E
values for Aoroides, Cvclasois, haroacticoid copepods,
small bivalve siphons and Macoma.
These fish had nearly
neutral' E values for Capitella, Armandia,. and Coroohium;
and Oligochaetes and Streblospio were avoided,
The speckled
sanddabs overwhelmingly selected for Aoroides, but other
amphipods, mysids and crabs were also positively selected.
Sanddabs fed upon Capitella, Armandia, and Corophium in
about the same proportions as they were taken by the cores
at this station.
Streblospio, Oli!';ochaetes, and Macoma were
avoided by these-fish at the Dairy station.
Armandia, Caoitella, Notomastus, Phoronids, Oligochaetes,
and Cyclaspis were numerically very abundant in the cores
made at the Bridge station (Figure 18).
The medium-sized
starry flounders at this station had positive E values for
G·lycera, unidentifiable polychaetes, Aoroides, crabs, small
_bivalve siphons and whole bivalves,
These fish consumed
Armandia and Macoma in nearly neutral proportions.
Medium-
sized starry flounders avoided Capitella, Notomastus,
Phoronids, Oligochaetes, and Cyclaspis.
The large starry
flounders at _the Brid!>;e station fed preferentially on
Urechis cauPo, Glycera, large bivalve siphons and whole
bivalves.
and Hacoma.
These fish fed neutrally on Notomastus, ·mactrids,
The large starry flounders had a negative E
value for Armandia and this fish avoided the same type of
•
~9
?rey as did the medium-sized starry flounders at this station,
En~lish
sole had ?Ositive E values for Aoroides, harpacticoid
copepods, and small bivalve siphons. These fish ate Streblospio and Macoma in essentially the same ?roportions as
these prey .were taken in the cores at this. s.tation.
Armandia,
Capitella, Phoronids, Oligochaetes,·and Gyclaspis were
avoided by the English sole.
The S?eckled sanddabs had
positive selection for the same types of prey at the
Bridge
station as .. they did at _the Dairy station, .i.e,, Aoroides,
other amphipods, .and small bivalve siphons,
These fish had
negtrtive· E value· .for Armandia ,·:.Notomastus, Capitella, Phoronids, Ol-igochaetes, _and·cvclaspis.
In spite of the large number of benthic cores made at
the Ocean station (278), the food in the guts of the flatfish was not well represented by the cores at this locality
(Figures 18 and 19).
The large starry flounders consumed
primarily crabs and large bivalves at this station, whereas
the cores sampled primarily sma_ll crustaceans and polychaetes.
The English sole at this station had positive E values for
Polydora sp., Armandia, Streblospio, bivalves, and crabs.
These fish had neutral electivity values for Prionosoio
pvgmaeus and Euphilomedes carcharodonta, and avoided the
majority of the items taken in the cores.
The speckled
sanddabs selected for mysids, crabs, and other crustaceans
and avoided nearly all the organisms collected by the cores.
Large sand sole fed preferentially on fish and the small
sand sole on mysids,
There was no overlap at all between
40
the types of organisms taken by the cores and the major
prey categories eaten by both size groupings of sand sole.
DISCUSSION
Distribution and Abundance
Distributions and
mi~rations
of flatfish may be
influenced by many factors, including the search for
adequate food, changing physiological requirements
during life history, purposeful movements made without
regard to the environment, the avoidance of predators,
the type of substrate, and changes in the physical parameters of the environment such as temperature, salinity,
turbidity, oxygen content, nutrient levels and changes
in photoperiod (Fleming and Laevastu, 1956), The distribution of the flatfish throughout the study area varied
with respect to the season, the size classes, and the
species; however, why these patterns exist is very difficult
to explain.
The concentration of the small starry flounders at the
more inland portions of the slough and the larger flounders
closer to the ocean throughout the year is similar to the
distribution pattern of this species in the Columbia River
estuary (Haertel and Osterberg, 1967),
The availability
of food might be one of the major factors which is responsible
for this distribution of starry flounders in Elkhorn Slou!';h.
The large bivalves and llrechis cauoo which are very important
food sources for the
lar~e
starrY flounders are not found
abundantly at the most inland station, Kirby Park.
Coronhium
son., small polychaetes, and small bivalves that are the
41
42
staoles iri the diets of the smaller size starry flounders
are quite abundant at the lower portions of the slough.
Elkhorn Slough appears to function as a nursery and
feeding ground for young English sole, since no individuals
larger than 150 mm were ever taken inside the slough.
The
absence of the English sole from the study area during the
winter did not appear to be induced by a decrease in the
availability of food or by marked changes in temperature,
salinity, or nutrient content of the water (Smith, 1974).
A decrease in the photoperiod might have some influence on
this distribution pattern; however, this does not explain
whv the English sole are not found in the most inland
regions of the slough but are abundant near the Bridge
station from August through October.
Similar patterns
of the young English sole moving into deeper waters during
the winter have been observed in British Columbia (Ketchen,
1956), Oregon (Westrheim, 1955), and Humboldt Bay, California (Misitano, 1976).
Speckled sanddabs are limited in their distribution to
the outer regions of the slough and offshore areas.
During
much of the year, the water temperature, salinity, oxygen
content, and the other hydrographic parameters do not appear
to differ enough between the inland stations and the more
seaward stations to form barriers to the use of the entire
slough by these fish (Smith, 1974).
The types of food at
Kirby Park also do not seem to be a limiting factor in their
distribution.
The primary limiting factors are more likely
43
the substrate type and the turbidity of the water.
The
bottom sediment becomes softer and the transoarency of the
water
ocean.
~>;enerally
decreases progressi,lely inland from the
The speckled sanddabs rely on sight for feeding and
they pick their food from the bottom without
extraneous material (Ford, 1965).
consumin~
much
The poor visibility in
the wa.ter at Kirby Park and the silty sediment might make
it difficult for these fish to feed effectively.
Of all the flatfish studied, the sand sole were the most
limited in their distribution, being restricted to the Ocean
station ·throughout the year.
The muddy substrate -of the
s laugh might not be suitable _for the sand sole.
These fish
also appear to feed by sight (Miller, 1967) and probably
require fairly clear water in order to capture their active
prey.
There must also be sufficient food (fish and mysids)
available, to· them in the offshore waters.
Morphometric Relationships
The results of the morphological measurements and the
feeding habits of the flatfish species in this study agree
with many of the findings in previous studies on the relationships between morphology and trophic ecology.
Alexander
(1970) stated that fish with larger mouths can better feed
on active prey and grasp prey from the side, whereas fish
with smaller mouths can better suck in their prey.
The
sand sole, which feed on active mysids and fish, and the
soeckled sanddabs, which primarily eat active crustaceans,
44
have the largest relative mouth sizes.
Starry flounders
and English sole have smaller mouths and concentrate
their feeding on the less active polychaetes and bivalves.
Hatanaka et al (1954) found that the teeth of annelideating flatfish are more numerous and better developed
on the blind side than on the eyed side of the flatfish,
and s_uch was the case with the English sole and starry
flounders.
They also contended that the pharyngeal teeth
are usually not well-developed for annelid-feeders hut
often form grinding plates for flatfish that eat molluscs,
The annelid-eating English sole and small starry flounders
had very weak 1Jharyngeal teeth, but the large starry flounders, which frequently eat whole bivalves, have pharyngeal
teeth that form strong grinding plates,
The speckled sand-
dabs and sand sole have canine teeth on both dorsal and
ventral jaws for piercing and holding their active prev.
Hatanaka et al (1954) also found this to be the case with
other species of flatfish that feed on mysids and fish.
The structure of
~he
gill rakers also gives an. indi-
cation of the type of food consumed, since the·space
between gill rakers controls the minimum size of the prey
that can be eaten, especially for active prey.
De Groot
0971) found that polychaete-mollusc feeders usually lack
large gill rakers and crustacean-feeders have long, more
developed gill rakers.
This is also true for the starry
flounder, which have stubby gill rakers, and for the speckled
sanddab and sand sole, whose gill rakers are long and well
45
developed,
However, the English sole have relatively large
gill rakers, contrary to what should be expected according
to de Groot.
This observation helps to confirm Yasuda's
(1960) finding that stronger correlations exist bet,veen
mouth sizeo and food types than between gill raker length
and food types, especially for flatfish.
The relative proportions of parts of the alimentary
canal are also useful in the study of feeding habits.
Flatfish that feed on annelids and molluscs have long
intestines, whereas the intestines of flatfish that eat
fish and crustaceans are quite short (Hatanaka et al, 1954).
This is definitely true for the starry flounders with very
long guts, and the sand sole and speckled sanddabs with
relatively short guts.
The English sole again have somewhat
of an intermediate gut length, longer than those of the sand
sole and sanddabs, but much shorter than the starry flounders'
guts.
De Groot (1971) correlated flatfish that ate small prey
continuously with relatively long guts, and correlated others
that eat large prey sporadically with ~hart guts,
Starry
flounders and English sole have relatively long guts, but
small stomachs where very little digestion occurs.
Large
starry flounders, contrary to de Groot's findings, often
feed sporadically on large.prey such as_Urechis or large
bivalves, but the medium and small-sized starry flounders
and the English sole appear to feed continually during the
day on small prey,
Sand sole and speckled sanddabs have
relatively short guts but large stomachs in Which most of
46
the digestion takes place.
Sanddabs also appear to feed
contrary to the finding of de Groot, since they feed on
relatively small prey continuously during the day. Sand
sole, however, do seem to feed on large prey more sporadically.
This comparison of feeding frequency among the flatfish
is possible because the various species of flatfish appear
to have similar gastric emptying rates.
Different prey
categories are digested at different rates under different
conditions (Windell, 1967); but, in general, complete
digestion and gastrointestinal tract evacuation for small
fish takes less than 14 hours (Ford, 1965; Tyler,_1970).
Immature European flounders (Pleuronectis flesus), which
resemble the starry flounders in morphology and general
biology, clear the entire alimentary tract of food in 19
hours (Arndt and Nehls, 1964).
Cumulative Prey Analysis
It has long been believed that in estuarine systems
the number of invertebrate prey species available to the
fish should decrease from the ocean to the more inland
portions of the environment (Hedgpeth, 1937; Frolander, 1964).
The cumulative number of prey categories from the pooled
number of fish (Figures 9 and 10) shows this to be true in
Elkhorn Slough, but also that the number of fish that have to
be
sampled in order to obtain an adequate estimate of avail-
47
able
~rey
also decreased from the ocean to the more inland
portions of the environment.
Dietary Variation with Size and Season
The diet of some fish has been shown sometimes to vary
with the size of the fish and/or the season (Orcutt, 1950:
Bregnballe, 1961: Haertel and Osterberg, 1966; Miller, 1967:
Levings, 1974).
The changes in the diet of the starry
flounders and the sand sole seem to agree with the findinp;s
of other researchers who found that fish normally eat the
largest prey that they can unless small prey are abundant
and densely concentrated, or if large prey are unavailable
(Hall~
al, 1970).
As starry flounder and sand sole grow,
they feed on different types of larger prey categories,
even thoup;h the prey types that. they ate when they Here
smaller still remain abundant.
These changes in diet t<ith
size could not be observed in the English sole and speckled
sanddabs since all the individuals examined were small and
had fewer prey types that were potentially available to them.
The lack of seasonal variation of the feeding habits of
the flatfish in this study is not surprising since the major
prey items of the fish were abundant throughout the year
(Nybakken et •1. 1976).
--
--
Hatanaka et al (1954) also found
no seasonal variation in the diets of the flatfish in
Japanese waters.
48
FeedinF, Frequency
Miller (lq67) indicated that adult female starry flounders stop feeding during the winter in Puget Sound, but that
the sand sole feed throughout the year.
Very few of the guts
of any of the flatfish taken during this study were empty.
This might be because the majority of the fish examined were
immature, since according to Schaeperclause (1933), younger
fish have higher energy requirements
t~an
do older fish and
have to eat more frequently; therefore, the probability of
finding young fish with empty stomachs is less than for
finding older fish with empty stomachs.
Feeding Within a Location
The type and abundance of prey species eaten by flatfish
mav vary from one locality to another (Hertling, 1928;
Blegvad, 1930), but in order for these patterns to become
distinct, the fish must feed within a locality for a relatively long period of time, to prevent overlap of prey<
The
Percent Similarity Index values for the prey of each flatfish category between adjacent stations (Table 7) and percentage unique prey categories between adjacent stations (Table
8) indicate that those fish examined must have been feeding
within each locality lonF, enough for distinct patterns to
occur.
The time required would probably be somewhat less
than the 12-19 hours required for complete alimentary tract
evacuation by these small flatfish.
49
Tagging and recapture experiments with the starry
flounders within the study areas also indicated that this
species has a relatively small home range at least during
part of its life (Nybakken
~
al, 1976).
Manzer (1952)
also found that starry flounders in British Columbia usually had small home ranges.
Feeding Strategies
Speckled sanddabs and sand sole appear to employ different feeding strategies than starry flounders and English
sole.
Sanddabs and sand sole localize their prey by sight
(Ford, 1965; Miller, 1967).
Starry flounders and English
sole, particularly in very turbid waters of the inland
regions of the slough, probably rely more on olfaction
than on visual cues,
Plaice (Pleuronectes ulatessa), which
closely resemble English sole in feeding habits, morphology,
and general biology, and European flounders also have a
highly develoued olfactory sense (de Groot, 1971).
De Groot
also found that plaice and European flounders are able to
detect a small jet of water more easily than dab (Limanda
limanda), which are quite similar to the speckled sanddabs.
Perhaps English sole and starry flounders in the natural
environment are attracted by the small waterflow of these
siphons as well as by visual stimuli; whereas, speckled
sanddabs have to rely almost entirely on visual input. This
might partially explain why English sole and starry flounders
so
consume more bivalve siphons than do sanddabs.
The large amounts of extraneous debris in the guts of
English sole and starry flounders indicate that these fish
are capable of feeding by plowing through the substrate.
The large size of some of the starry flounders within the
study area permits them .to forage deeper into the sediment
than the English sole can reach.
Speckled sanddabs and
English sole are readily attracted by sediment disturbances
or by the vibration created by.digging small holes in the
substrate (L. Hulberg, pers. ·comm.).
The disturbances of
the bottom--by -larger fish-,--Such-.as .starry flounders or Myliobatus californicus (MacGinitie, .1935), are probably of benefit to speckled sanddabs and English sole by dislodging previously unavailable food organisms from the sediment,
Flatfish Feeding Habits tvith Respect to Prey Natural History
The natural history of prey can often provide clues as to
hotv and where the fish are feeding.
Streblospio benedicti,
and Capitella capitata are small, surface, tube-dwelling
polychaetes that would primarily be available to fish that
feed by foraging through the sediment like English sole and
starry flounders.
These polychaetes would normally be
available to speckled sanddabs only after the sediment was
disturbed by one of the grubbing-type feeders.
The abundance
of Streblospio in the benthic core decreased seaward from
Kirby Park (Nybakkert, 1976).
At the Ocean station it was
replaced completely by Priospio sp.
CaPitella was most
51
abundant at the upper regions of the slough and it could
also be found at the head of the Monterey Submarine Canyon
offshore.
Armandia brevis is more active than the previous
species and it is known to swim up into the water column
(Hermans, 1966).
This polychaete is eaten whole by all the
flatfish, but its small size causes it primarily to be consumed by the smaller fish.
the Bridge station,
Armandia was quite numerous at
Its abundance decreased progressively
inland from this station and offshore.
Magelona sacculata
is a small polychaete eaten only by the fish taken offshore.
Large, deep dwelling polychaetes, such_as Glycera sp. were
available only to the large starry flounders.
English sole
and speckled sanddabs are most likely to nip the tentacles
of the tube dwelling terebellid polychaetes but not fatally
damaging this potentially renewable food resource.
Oli~o-
chaetes were quite numerous throughout the slough, but they
were not found commonly in the guts of the flatfish,
Either
the fish could effectively avoid eating them, or, these quite
delicate annelids were consumed but rendered unidentifiable
extremely quickly in the fish's digestive process.
The flat-
fish often did not feed upon the whole polychaete and the
uneaten portion might, in many instances, be able to regenerate itseif (Dales, 1970).
The large starry flounders Here the only flatfish that
consistently ate the deep, tube-dwelling Urechis cauno.
Urechis have been observed to come partially out of their
burro,~,
but the large starry flounders were probably capable
52
of burrowing deep into the sediment in order to feed upon
these worms.
This was evidenced by one individual having
eaten a Urechis, a commensal pea crab (Scleroplax granulata), the commensal polychaete (Hesperone adventor), a
~
commensal fish (Clevelandia ios) and a considerable amount
of detritus, all at the same time.
Urechis was most abun-
dant at the upper portions of the slough but it was not
found offshore at all.
This worm is also heavily preyed
upon by the leopard sharks, Triakis semifasciata in the
slough (Talent, 1973).
The major crustaceans in the slough were• the amphipods (Corophium spp., Aoroides columbiae, and Caprella
spp.), a cumacean (Cyclasois sp.), and the mud crab (Hemigraosus oregonensis).
Coroohium and Aoroides are small,
slow-moving, surface, tube-dwelling amphipods that all the
flatfish are capable of eating whole.
Speckled sanddabs
feed most on Aoroides at the Dairy station •.. Coroohium
was quite abundant in cores from Kirby Park, and Aoroides
,.,.as numerous only in cores from the Dairy and Bridge
stations.
Caorella was eaten only by speckled sanddabs
at the Bridge station.
This amphipod is known to be
associated with hydroids and. swims up into the water
column (Rickets and Calvin, 1968).
Cyclaspis is a small
epibenthic cumacean found throughout the slough.
This
cumacean was significantly fed uoon by only the English
sole and small starry flounders.
Large
starr~flounders
probably consume Cyclasnis as well as the harpacticoid
53
copepods only incidentally with the debris consumed while
foraging for larger Prey items.
Offshore, the fish fed upon different species of crustaceans.
The fast swimming amphipod Atylus tridens· and
the slower swimming epibenthic amphipods Monoculoides spp.
and Synchelidium spp, were fed upon primarily only by the
speckled sanddabs,
As previously mentioned, the fast
swimming mysids are also extremely important in the diets
of speckled sanddabs and small sand sole.
Lamprops sp.
and several other epibenthic cumaceans are more important
in the diet of the English sole than in any other flatfish.
An active swimming ostracod, Euphilomedes sp,, was quite
abundant at the Ocean station and was eaten frequently
by
on~y
the English sole and speckled sanddabs,
Small
sand nestling juvenile Cancer magister and a crab that is
commensal in crab burrows (Pinnixa
franciscana)~e
eaten
more numerously by the starry flounders than by any other
flatfish,
Although the sand sole is physically capable
of eating crabs, it was the only flatfish taken offshore
which never contained this abundant prey item,
The large
starry flounders often had fragments of Dendraster ex .. centricus in its guts, along with crab exoskeletons,
These
fish might possi91Y have eaten sand dollars secondarily
while trying to feed on the crabs that hide in the Dendraster beds for safety.
Several bivalves were consumed in large numbers by the
flatfish in the slough• Gemma
gemma, Macoma spp., Saxidomus
54
n1ltta lli and Tresus nlltta llii.
Gemma is an introduced,
small, soft-shelled clam that was found primarily at Kirby
Park where it was fed upon by English sole and starry
flounders.
Macoma nasuta was by far the most numerous
small bivalve throughout the remainder of the slough.
This soft-shelled bivalve usually remains in soft mud
about 200 mm below the surface and extends its incurrent
siphon to the surface.
MacGinitie and MacGinitie (1949)
observed that Macoma may project the tip of its siphon
as far as 20 mm above the mud and wave it back and forth
while feeding.
This motion
quit~
probably attracts the
attention of the flatfish.
The flatfish are quite prudent predators (Slobodkin,
1968) in feeding heavily upon these siphons since the
clams are able to regenrate the siphon tips and live to
feed a flatfish in the future.
Whole Macoma were occa-
sionally eaten by the starry flounders and English sole,
but not nearly as frequently as the siphon tips were
cropped.
The large size of the Saxidornus and Tresus
siphons·usually prevented all the flatfish, except the
large starry flounders, from feeding on them.
Offshore, the hard-shelled Clinocardium nuttallii,
that lives in coarse, moving sand, was swallowed whole by
large starry flounders.
Siligua sp. was also consumed
occasionally by these fish, probably when these fast
burrowing bivalves were momentarily dislodged from their
burrows by a large wave or strong.current.
55
Fish are the staples of the large sand sole's diet.
Sand sole feed uoon many active fast·swimming fish, such
as Engraulis mordax.
In order to capture these prey, the
sand sole probably has to
lie camouflaged on the bottom
and ambush the faster fish as they pass,
also cannibalistic.
These fish are
When feeding on its young it could
actively search for the food and swim after and overtake
the slower fish,
In spite of the high abundance of
speckled sanddabs offshore, sand sole fed very little on
these fish; perhaps the reason for this was the sanddabs
are quite alert fish and are able to successfully avoid
the larger sand sole.
Trophic Diversity: Generalists Vs. Specialists
Springer (1960) and Keast (1970) found that the trophic
diversity may be greater for larger fish,
This conclusion
might appear to be valid since large fish are potentially
capable of consuming a greater range of prey sizes than are
smaller flatfish,
In this study, however, several of the
smaller flatfish had mean individual-•trophic diversity
values that were higher than those of larger flatfish
(Table 9),
This apparent contradiction is due to the
higher number of small orey categories in the environment
than larger prey categories.
McNaughton and Wolf (1970) state that the most numericallY abundant or dominant species usually have the highest
56
niche breadth and the trend in this study follows, with
the English sole and speckled sanddabs being numerically
the dominant flatfish at the majority of the stations and
also having the
values,
hi~hest
mean individual trophic diversity
The starry flounders were only numerically.dominant
at the Kirby Park station, but at this locality these fish
had their highest individual trophic diversity values.
The sand sole were among the least abundant of all the
flatfish studied and they had the lowest mean individual
trophic diversity values.
Animals may be classified as trophic generalists or
specialists based upon the breadth of food types consumed
and by the size of the repertoire of feeding behavior
(Schoener, 1971),
English sole are the most generalized
feeders of all the flatfish studied, since they not only
had the highest mean individual trophic diversity (Table
9), but are
able to feed throughout the study area.
English sole are also generalized morphologically in that
their morphological characteristics are intermediate
between the crustacean-fish feeders such as the sand sole
and speckled sanddabs, and the polychaete-mollusc feeders
such as the starry flounders.
The speckled sanddabs are
also trophic generalists since they have high individual
trophic diversity values, but are more dependent in feeding
on crustaceans and appear to require better water visibility when feeding than do English sole,
The starry
flounders should probably be considered as generalists
57
in spite of their comparatively low mean individual trophic
diversity values because they eat a wide range of prey
types and are able to feed under a
mental conditions.
'~ide
variety of environ-
Sand sole are specialists since they
have a very low individual trophic diversity and appear to
be restricted to sandy areas with relatively good water
visibility.
In areas like the slough where food is abundant and
fluctuations of its abundance occur in either time or soace,
trophic generalists are,favored.
The majority of the fish
in the slough appear to be generalized enough in their
feeding repertoire to enable them to "switch" somewhat
their mode of feeding in order to utilize the various prey
items at different localities.
At the Ocean station, where
the food resources are less abundant, greater specialization
on particular kinds of food appears to be important.
Flatfish feed more heavily within a major prey grouping,
such as polychaetea, mollusca or crustacea at the Ocean
station (Figure 11), in spite of the overall increase in
the number of prey categories eaten at this locality.
Crustaceans dominate the diet of the speckled sanddabs at
the Ocean station much more than any other single major
prey taxon did at the slough stations.
Similarly, the
English sole's diet is much more specialized for polychaetes at the Ocean station than in the slough.
58
Dietary Overlap
One theory is that fish have overlapping food niches
only when food resources are superabundant and discrete
niches when abundance of orey is reduced (Keast, 1965:
Nilsson, 1967: Zaret and Rand, 1971).
This is consistent
with my findings, since the niche overlap values are generally much higher between fish in the slough than from
the Ocean station (Table 10).
The apportionment of food
resources among the flatfish species appears to be much
more distinct at the Ocean station than at the slough
stations.
The only exception to this trend is the high
overlap in the diets of the speckled sanddabs and the small
sand sole, indicating ontogenetic competition.
The high
overlap is exclusively due to feeding on one species of
mysid, Acanthomysis davisii.
This mysid is known to swim
in schools close to the bottom and this aggregation could
possible explain why it is consumed in such large numbers
by these two flatfish.
The trophic overlap value was high at the Bridge station
for English sole and speckled sanddabs than at any other
locality.
The clarity of the water and the sandy texture of
the substrate at the bridge are more conducive to the visual,
picking-type of feeding by the sanddabs than are the conditions further into the slough, thus allowing it to compete
more strongly with the English sole for the quite abundant
polychaete and bivalve resources at this station,
The
59
medium-sized starry flounders also had .their highest value
of trophic overlap at the Bridge station, but it was less
abundant numerically at this station than at any other in
the slough.
The high competition and low abundance of the
medium-sized starry flounders could possibly suggest that
these fish are being competitively excluded from the use
of the resources in the seaward regions of the slough.
Electivity
The traditional attitude about northern demersal fish
is that they are generalists (Ogilvie, 1927).
More recent
studies show that these fish are not indiscriminate feeders
(Jones, 1952; Richards, 1963; and Rae, 1969).
Problems
with patchiness of prey, avoidance of the sampling device
by the prey, and the distribution of large prey outside
the depth range of the coring device all prevented the
making of complete estimates of the availability of all
types of prey to the flatfish.
These inadequacies are
reflected in the lot.; percent similarity index value:; for
the food eaten by the fish and the organisms taken with
the benthic cores.
Nevertheless, the availability esti-
mates were sufficient to demonstrate that the different
fish selectively feed uoon different prey categories and
that the electivity is not as finely develooed in the starry
flounders. English sole, or speckled sanddabs as it is in
the sand sole.
60
MacArthur (1958) stated that different species eat
differ~ent
food for only three reasons1 1) they feed in
different places or different times of day; 2) they feed
in such a manner as to find different food; and 3) they
select different kinds of food from among those to which
they are exposed,
A combination of these reasons is
sufficient to explain why the flatfish, despite their
propensity for opportunistic feeding, are able to apportion the resources of the study area in a manner that
minimizes competition, except in areas where the resources
are superabundant.
61
Table L
Seasonal percent abundance (%A) and mean number
per 10 minute otter tra,.;l to,., (N/T) of the major flatfish
soecies by locality
May '75
-July'75
+Aug-Oct' 74
Aug-Oct'75
N/T
%A
N/T
%A
N/T
3.4
2.4
0
8
91
1
5.4
58.4
0.2
309
98
0
2
5.9
0
0.1
3.3
7.6
1.3
10
20
70
Nov,' 74
-Jan. '75
Feb. '75
-Apr. '75
%A
N/T
%A
3,4
P. stellatus
100
0
P. vetulus
0
0
0
c. stigmaeus
32
Number of fish
63
37
0
KIRBY PARK
33
59
DAIRY
P. s.tellatus
P. vetulus
c. stigmaeus
Number of fish
68
0
32
1.6
0
1.3
72
17
11
28
2.0
1.0
0.6
24
65
11
82
47
1.4
3,0
6.3
129
BRIDGE
3. 8
0
30.2
118
30
9
61
14. 7
2.8
11.8
153
22
34
44
5.5
8.5
11.0
100
7
38
55
7 .o
31.0
57.0
384
P. Stellatus
11 0.4
P. vetulus
0
0
c. stigmaeus
78 2.0
P, melanostictus 11 0.3
Number of fish
18
17
8
61
14
1.7
0.7
5,9
1.4
8
63
17
12
0.7
0.2
1.4
1.0
8
17
35
40
1.5
2.8
3.2
P. stellatus
P. vetulus
C. stigmaeus
Number of fish
14
0
85
OCEAN
89
84
O,R
129
62
Table 2,
Fish collection locations, methods,and times
Kirby Park
Month
1974 August
O.T,
B.S.
O.T.
Ocean
Bridge
Dairv
B.S.
o.T.
B.S.
1*
2*
1*
September
2*
1*
1*
October
2*
1*
1*
November
1*
December
4*+2
3*+2
1*+1
3*
4+(2)
4
2+(1)
4
February·
2
2
3
4
March
1
2
2
Aoril
2
4
4
2
May
1
2
1
3
June
2
2. (1)
2
4
July
3
3
1
3
August
2
2.
1
4
September
2+(1)
1+(1)
1
4
1975 January
October
2
36
2
-2-
1+~1 ~
38
4*
(1 )*
2*+(1 )*
1
-1-
l
25
B.S.
O.T.
3*+(1 )*
2
2
2
4
4
47
2
Totals
O.T. (Otter Trawl)
B.S. (Beach Seine)
*
(
=
)
5 minute tows.
tows
= Night
=
=
All other tows 10 minute duration,
146
7
m
63
Table 3. ~ean ratios, X, and standard deviation values, SD,
for the standard len~th to the length of the maxillary on
the ocular side. * ~ the ratio for that species is si~nif­
icantly different from the ratio of any other species at
p = .001; t-test.
Species
Number
Examined
Size
Range(mm)
Standard length(mm~
Maxillary on ocular side(mm)
X
SD
Platichthvs
stellatus
25
R0-325
14.41 (.9R)*
Paroohrys
vetulus
26
40-142
16.3R (.7fl)*
Citharichthys
stigmaeus
32
37-125
11.43 (.73)*
Psettichthys
melanostictus
26
3R-252
10.1R (.39)*
64
Table 4. Mean ratios, X, and standard deviation values,
SD, for the standard len~th and stomach lengths to the
length of the entire gastrointestinal tract. * = significance levels same as in Table 3;
Soecies
Number
Examined
Standard length
Gl_tract length
X
SD
Storoach length
Gl tract length
SD
X
Platichthys
stellatus
126
.77 (,09)*
.15 (.02)*
Paroohrys
vetulus
112
1.06 ( .17)*
.23 (.04)*
Citharichthys
stigmaeus
126
1.16 ( .17)*
.33 (.03)*
Psettichthys
melanostictus
40
1. 34 (.15)*
.35 (.04)*
65
Table 5,
Kendall tau rank correlation coefficients of
Index of Relative Importance values of prey categories,
IRI, between different size classes within a flatfish
species by station and season. N = the number of fish
examined. NS = the IRI rankings were not significantly
similar at ,05 probability level.
Species (N)
Station
Season
Tau
A(l5 )xB ( 11)
Kirby Park
May-July '75
.35
.05
B(7)xC(8)
Dairy
May-July '75
.28
NS
B(9)xG(l5)
Bridge
Feb. -Apr. 4 75
.21
NS
D(25)xE(l4)
Kirby Park
May-July '75
.54
.001
F(l9)xG(15)
Ocean
Aug. -Oct. '75
.45
• 01
H(31)xi(6)
Ocean
Aug.-Oct. '75
.14
NS
= Platichthys stellatus ~99 rnm
= Platichthys stellatus 100-199 mm"
c = Platichthys stellatus 200-299 mm
D = ParoJ2hrys vetulus sao mm
E = Paro12hrys vetulus >80 mm
F = Citharichthys stigmaeus <80 mm
G = Citharichthys stigmaeus )80 mm
H = Psettichthys melanostictus ~150 mm
I = Psettichthys melanostictus >150 mm
A
B
Significance at
Probability levels
66
Table 6_, Mean Kendall rank correlation (Kendall, 1962) of
Index of Relative Importance values of prey categories among
seasons for each flatfish grouping at each locality.
X =No fish, Probability levels: * = ,05; ** = ,01; and
*** = ,001.
i
Species
Kirby Park
Dairy
Bridge
Platichthys
.
stellatus (1 00-199 mm)
.41***
.34**
.43*
.• 33*
.31*
.• 34**
.56***
.SO***
,53***
.52***
.42**
,49***
Platichthys
-s-t-ellatus (200-299 mm)
Paro2hrys
vetulus
Citharichthys
stigmaeus
X
.48***
X
Ocean
X
67
Table 7.
Percent similarity indices for the combined prey
of all individuals of each flatfish category between adjacent
stations. X =No fish.
Species
Kirby Park-Dairy
Dairy-Bridge
Bridr,e-Ocean
Platichthys
stellatus (100-199 nun)
41.7
50.3
Platichthys
stellatus (200-299 nnn)
X
52.9
12.9
52,3
32•0
35.8
26.4
ParoQhrys
vetulus
Citharichthys
stigrnaeus
45.8
X
X
68
Table~ 8.
Percentage of unique prey categories bet1veen
adjacent localities by flatfish grouping. X = No fish.
KP =Kirby Park, D = Dairy, B =Bridge, and 0 =Ocean.
KPxD
DxKP
DxB
BxD
BxO
OxB
Platichthys
stellatus (1 00-199 mm)
38"/.
24%
51%
15%
X
X
Platichthys
stellatus (200-299 mm)
X
X
21%
35%
31%
45%
42'7'.
23%
11"/.
43%
29%
41%
X
X
15%
46%
28%
42%
Species
Paro2hrys~
vetulus
Citharichthys
stigmaeus
All values in these paired comparisons refer to the
first location listed, For example, in P. stellatus (100199 mm) 38% of the prey categories eaten at Kirby Park
were unique when compared with the Dairy station. while
24% of the prey categories at the Dairy did not occur-. in
this flatfish taken at Kirby Park.
Table 9. Troohic diversity summary. N = the total number of individual prey
items. S = the total number .Qf prey categories. F = the number of guts analY7.ed which contained food, H (SD) = the mean Brillouin trophic diversity in
individual ~uts and (one standard deviation), M.H. =the median trophic
diversity it1 individual guts, J (SD) = the mean evenness component of. trophic
diversity i1:1 individual guts and (one standard deviation)
Station
Species
N
s
F
H(SD)
Natural
bels
MH
J(SD)
KIRBY PARK
P.stellatus ( ~99mm)
P. stellatus (1 00-1 99mm)
P.vetulus
355
3751
105R
11
39
31
15
R3
50
.59(.355)
,56(,356)
,87(.396)
.64
.57
.95
.63(.233)
.65(.274)
.76(.189)
DAIRY
P.stellatus (1 00-1 99rrun)
P.stellatus (200-299mm)
P.vetulus
c.stigmaeus
2933
396
1392
1931
31
25
43
37
32
27
52
65
.49(,371)
.37(.357)
,89(,466)
.53(.347)
.44
.49
.86
.53
.55(.269)
.71(.294)
.75(.189)
.58(.231)
BRIDGE
P.stellatus (1 00-199mm)
P.stellatus (200-299mm)
P.vetulus
c.stigmaeus
228
2598
5455
4281
17
31
67
60
17
53
112
177
.43(.387)
.36(.376)
• 85 (. 431)
.75(.434)
.35
.32
.89
.84
.60(.340)
.79(.284)
.66(.230)
• 72(. 233)
OCEAN
P.stellatus (200+mm)
P.vetulus
C.stigmaeus
P.melanostictus (5.150mm)
P.melanostictus ( > 150mm)
434
3863
1188
502
70
39
81
74
16
13
28
43
97
39
16
.53(.435) .38
1.00( .455) 1.10
.51(.408) .56
,30(.310) .34
.12(.196) .10
.65(.204)
.61(.229)
.80(.194)
.79(.198)
.86(.317)
en
"'
70
Table-10.
Index of overlap, c,~ , between flatfish categories
within a locality. P.stel.= Platichthys stellatus, P.vet.=
Paroohrvs vetulus, C. stip.;.= Citharichthys stigrnaeus, P.mel.=
Psettichthys melanostictus. X= No fish
P.stel. P.stel. P.stel.
< 99mm 100-199 200-299
P. stel.
$. 99mm
~
.54
~
X
P.stel.
200-299
X
P.vet.
X
,84
X
.48
C.stig.
C.stig.
.88
X
K
P, s tel.
100-199
'
X
P.vet,
• 09
.72
X
I
R
X
B
ly
-
~-
X
X
p
·-·-
-
• 03
-~
.06
.47
A
R
K
X
~-
DAIRY
P.stel;_ P.stel. P.vet.
200+ mm 100-199
P.stel
200+ mm
i~
P,stel.
100-199
X
P.vet.
X
~
.93
• 95
X
X
~
-
X
• 85
B
X
R
X
D
G
I
~
X
X
0
.91
~
0
X
0
0
0
P.mel
150
>
X
0
P.mel.
:::;- 150
-
.
.04
.07
,03
> 150
.11
X
C.stig.
-p .mel.
.11
X
.11
C.stig. P .mel.
<-150
E
---
X
~
71
Figure 1.
Map of study area.
are hatched.
Regular sampling areas
72
-
·.·:
.
.. ..
..- .
OCEAN
- ·.. .
-~ .·- .... - . - .- -.-
73
Figure 2,
Length frequency histograms for Platichthys
stellatus by season and locality.
starry flounder caught.
+ one standard deviation.
N
=
the number of
SL = the mean standard length
NOV. '74- JAN.'75
%N eo
KIRBY
PARK
N•32
S.L.=\39± 2 9.3
60
FEB.- APR.'75
MAY- JUL.'75
N• 2.1
5Lal69±14.8
AUG.- OCT.'74
AUG.- OCT. '75
N •27
N •58 ·
S.La\25± 21.8
S.L.-\09 ± 42.8
-
40
20
0
%N eo
D,l'\\RY
N•l9
SL.• 217±62.5
60
N•34
SI..=214±56.o
N•20
S.L.•236±55.7
N•l3
SL.=22\ ±5\.5
N•22.
N•26
S.L.=2.72± 56.5
40
20
,..
0
%N eo
BRlDGE
60
N•l7
SI..=213±83.7
N•45
SI..=237± 55.4
S.L.=2.69±52..9
N=2
S.L.=282±38.0
N=l5
SI.=231±44.3
N=7
S.L.=2.70±34.7
40
20
0
%N eo
OCEAN
60 .
.--.-40
•
20
0
+ + + + + + + + +
t.n 0
tnOtnOtnO!!>
- LfJ to C\1 tO 0> N
V'OJ---C\lC\JC\lf()
.
. cdl,, .frn
'+ + + + + + + + +
U)Ol!>OiilOI!'l
Ill
o - Ill ro ~.. Ill
a> '"
VCO---•••
C'IJC\1{0
N•ll
SL.• 2.36 ±33.95
•
r-
1-
h
75
Figure 3,
Length frequency histograms for Parophrys
vetulus by-season-and-locality.
English sole caught.
N =the number of
SL-= the mean standard length+
one standard deviation.
FEa-APR. '75
%N
KIRBY
PARK
MAY-JUL.'75
AUG.-OCT. '74
AUG.-OCT. '75
BO
60
40
N=l2
S.L.=41±9.3
N=2BI
S.L.=72±13.4
N•B
S.L.=57±B.O
N•53
S.L.=B3±14.3
N=O
20
0
%N so
DAIRY
60
40
87
-
r-~26
S.L.•IOI±I1.2
n
20
0
%N
BRIDGE
BO
60
40
N=l4
S.L.=30±5.7
N=34
. S.L•73±16.1
N=l45
S.L.=I03±13.9
20
%N
OCEAN
0
BO
/
60
40
N=7
SI..•I07±140.1
•5:3
SI..=I02±17. 5
20
0
+++++++++
oll)ol/loltlel(l;?
C\Jr"lt{)<Dcoc.n---
+++++++++
oll)ol/loll)omo
Nr<JU')(J)CJlOl=-~
N•22
S.L.=134± 67.2
JbD
~++++++++
o 100 1!)0 toOl!) o
C\lt()l{)t0C0(0=~~
77
Figure 4,
Length frequency histograms for-Citharichthys
stigmaeus by season and locality.
speckled sanddab caught.
+ one standard deviation.
SL
=
N
= the
number of
the mean standard length
.-
NOV. '74-JAN.'75
(':J
FEB.-A?R.'75
AUG.- OCT'74
AUG.-OCT. '75.
MAY- JUL.'75
N so
l.>o
DA!RY
60
N=9
S.L.=66±19.6
N=5
S.L.=53± 18.5
N•90
S.L.=72±5.6
N•9
S.L.•66±9.2
40
20
0
r-1lr-lrl[h
nf
I
0
-
~N 8o
BRIDGE
60 -
N•IOI
S.L.=70±12.5 ·
N 2 94
S. L.= 48± 10.9
N•213
,s.L.•70± 6.8
N= 44
•
S.L.=60± 14.1
-
40
-
20
r
0
"''N
J,l
OCEAN
h
8o
60
40
N=l4
Sl.•64±11.1
ril
2: l~ JJ]++ ~
+ + +
oo
oooooooooC\l
C\lt0<:tU'"JlDt--COOl-;-
. N•55
SI..•77±21.3
.n~~~
!r+++++++++
oo
oooooooooC\l
C\l t0 <:t U') tO t-- co Ol - -
STAI'\DARD
N•44
lf.l..•76±22.7
N=14
S1..=49±22.9
if.
++++++++++
.
00
oooooooooC\l
C\lt0<:ttOlDt--COOl--
LENGTH
(m.m.)
_n
+ + + + +
+ + + + +
oooooooo8~
C\lt()<:j-tl'.llOt--OJOl--
79
Figure 5.
Length frequency
~-mel:anostictus--by
-season
sand sole caught.
standard deviation,
SL =
~and
histograms for Psettichthys
locality.
the~mean
N = the. number of
standard
length~~
one
80
OCEAN
NOV. '7~·~ JAN.'75
-
40
-
N=2
S. L.= 94±31.1
2
FEB.= APR.'=f5
%N
N=l2
S.L.=221 ± 90.7
4
20
-
0
MAY-JUL.'75
%N
N=IO
S.L= 18 6 + 6 9.4
40
20
0
AUG.~ OCT. '75
%N
N=51
S.L.=99±62.0
40
20
0
0
VJ
+ + + + +
I
+
o-=:L-
+. +
<D-<D _ ( ! ) _
LO<O-_lO(l)C\JLOU>
<;;J· ".1· ro - - C\.1 C\.1 C\.1
STANDARD LENGTH (i!l.ril.)
81
Figure 6.
Linear regression of the maxillary length
to the--standard ·length-by -s·pec·ies. c·r =-correlation
coefficient.
82
20.0
I
I 0.0
•
E•
E
0
16.0
0
14.0
0
/
I 2.0
b.
e3
~:j
I 0.0
0
0
6
0
8.0
~C
<~
Ol
6.0
c
(9
_j
P. melanosticfus
4.0
C. stiqmaeus
P. stellatus
P. vetu/us
'
c.
r= .99
=
=
=
0
r= .98
r= .97
r= .95
0
0
2.0
0
0
40
Standard
80
120
Lenath
;;J
160
200
(m.m.)
24·0
83
Figure 7.
Linear regression of the gastrointestinal
tract length to the standard length by species. r
correlation coefficient.
=
84
0
400
360
0
320
~
0
E; 280
E
........,.
.I::.
-c- 240
0
l:J)
c
(!)
_J
-c-200
(.)
c
""'"
Fl60
-
(!)
120
80
=
40
0
r= .97
0
r= .95
=
Pmelanoslictus
0
.
40
80
Standard
120
160
=
r= .93
eo
200
Length -~(rn.m.)
r= .96
240
280
85
Figure 8,
Linear regression of the gastrointestinal
tract -length to -the stomach -length. by- species,
correlation coefficient.
r =
'"
86
400
0
I
l
360
~
~320
~
E
-280
F""
0
~-
-<--
C))
6
0
;
240
_J
0
-u 200
0
I
~
-<.::>
160
/
0
120
D.
=
0
r= .94
P.vetu/us
=
0
r =.94
C. stigmaeus
=
0
r= .95
P. me/anostictus =
6
r= .98
80
40
0
20
Stomach
40
60
Length (m.nt)
80
87
Figure 9.
The cumulative number of prey categories from
the. ,pooled number_ of. fish. for each flatfish category at
the -Ki-rby Park and ·nairy statiotis.
l<IF<BY
88
PAR~<
40
30
P. ve tu Ius = L;
P.stel/otus (100-199 m.m.)= o
P.sfe//otus Cs99m.m.)=
o
20
10
0
40
J
20
r
10
0
ru
·-
~~l:!i
~~/o~
30
>
,..r-~-
DAIRY
~
0
_,....,.--o-o-
0
P. vetu/us
= "'
C.stigmoeus = o
4·0
30
P. stellatus
20
P.stel/otus
'
(I 00-199 m.m.)=o
(200-299m.m.)= o
10
0
0
I0
20
30
40
5o
60
70
Pooled Number of Fish
'
I
'
'
'~
80
90
.....
89
Figure 10.
The cumulative number of prey categories from
the pooled number of fish for each flatfish category at
.the BrLdge_and Ocean- stations,
90
8RlDGE
-~
80
60
~
6~
6_,-r-6-
or--o-o-
-o_.....-o...........-'
o_,....-_6~ P. vetulus ·-
6r
40
C. stigmaeus = o
P. stellatus (200-2~9 m.mJ= o
0~
20
6
0
OCEAN
80
t::r
/
60
6
40
0
o/o--0/
__..,-/
c/
-~
20
P.vefulus
= 6
C. stigmoeus = o
P.stellatus (200+m.mJ = o,
P. melanoslicfus (>I 50 m.m) = o
P.melanosfictus (sl5 0 m.m.) = c.
0
.0
20 . 40
Poo~~cl
GO .80
100. 120 lt;·O . 130 100
Nurnber of
Fish
91
Figure 111•
The numerical percent composition of the
major prey groupings for Platichthys stellatus, .. Parophrys
vetmlus, and Citharichthys stigrnaeus
by station.
92
KIRBY PARK
so
DAIRY
so
40
P. s/e/Jcius
40
30
60
N•32
30
P.. :SiiJIJa!us
N :JS
20
~
(:5 99 mm.)
"'E
:;J
-"'
c
20
0
10
"'
0
~
Q_
20
0
:.~
·a
40
0
30
~~
30
I!
P.sN/Jolus (100-199mml
r. N
0
P. .J.'r:!l!aTJ:r (200-2S"9IT'-'f0
N• 2.7
10
·.c 10
z
(I00-1~9m.m.)
•S3
~IUu/us
N • 52
20
r
P. velulus
N•-50
BRIDGE
50
P. slt;/lulu~ U00-199m.mJ
N •17
40
0
30
I\
a I<
N •53
· · ll
G
I"
10
"'E4o
.c
P.llcllalus
(2.00+mmJ
30
20
N•2B
P.s/~1/cfus (2.00-2.9Sm..m}
20
~
OCEAN
40
D
10
- 0
50
40
:;J
f! YfifU/1,/S
H=112
"E 2.0
Q)
0
~
"'
Q_
P.Yelutus
30
Z3o
N•43
20
10
10
0
40
0
40
C. sligmaeus
30
30
C. slijmaaus
N ~177
20
Major
Prey Groupings
N .. 97
20
Major
Prey
Groupings
93
Figure 12.
Percent composition in number (%N),
volume (%V) •~-and_ frequency of occurrence (%F .o. Y
of- prey-categories- -with- _~Index-
of~
Relative Importance
values-> 50 for Platichthys stellatus, Parophrys
vetulus, and Citharichthys stigmaeus, by station,
See Appendix Table A for list of prey category codes.
94
DAIRY
KIRBY PARK
Pr')'
"•
~
%N
f.
Prey Cate~ory Code
C!:lli!~iary Cc~~
""'
I
I
'"
"
0
~
i
%N
'%F.O.
I-bn. k d Sl;on N, Mcc i:li.
1
..--""l.C.-1
10
%V
0
•
I
"
%0
10
---
---
00
%V
I I I I fl~'t.ffi
P. s/~1/o/us (IOO-I99m.m.l
:~
0
Sn(S
%V
'"
~
%N
Tn{Sl A'J
::
~.
I -I lT
-- 1--~·
%N
'oo
0
10
%V
L
R stella/us
•
(200-2.99m.m.}
:'''"'k~~
- %F.O.
·~ - __ju _
_-[ ;(
P. 3/e//atus ( :S 99 m.m.J
<0
00
P. t't!lulus
10
%V
"kF.O.
•o
IL,_,Cc___.J
"'',_.,-.-_,_,_,__,.;..,_._-;--+-+-;--+-+-+--+-+-+--+-+--<-<
30-
%N
Dig
I
~:of---
%N
10
c.s/igmaeus
f! t'elu/us
%V ::\------'
%V
t--1 .. 2 0 '"I• F.Q.
BRIDGE
OCEAN
Pfro
5!&
"'
%0
%N
%V
P. .st~llatus ( 100-199 m.m.l
%V
%H
"'
·:::::1-
" .:___.,i. \ ' \ ' \
%V l:r -
r~
'liP~~
P. stel/alt..•s
__
{200+.m.m.l
"
%F.O.
%N
(2C0-2S9m.rn.)
%V
%.14
"10
'
%N
"/.V
- -
-
-
-
-
- -;t.F.O.
-
1!
95
~
'
I
l
l
I
I
Figure 13,
Percent composition,in number (%N), volume
(%V), and ·frequency of occurrence (%F ,Q,) of--prey
categories with Index of Relative Importance values
>50 for Psettichthys melanostictus at the Ocean station.
See Appendix Table A for list of prey category codes.
96
OCEAN
Prey
Category Code
70
. Adav
60-t------__:_I _ _ _ _...,
Dig
·-Nkad
Melo
Gran
50
%N
4030-
20
10
- - %F.O.
Q.
10
20
P.melonostictus ( :5150 m.m.)
30
·%v
4
50
60r---------------~
l
%N
I
l
Pisc
Em or
I
I
Pmel
I
I
I
Dig
201.__!_J-~~
10
'
-% F.O.
0
%V
10 }---L_~.J----L-1
20
P. melanostictus ( > 150 r:u.l.)
1---:--+-7--r'-!-~:-:-11---1--:~:--:--}
1--1 =20%F.O.
;
I.
97
Figure 14.
Frequency histogr~ms of individual trophic
diversity for Platichthys stellatus, Parophrys vetulus,
and_Citharichthys stigmaeus_bystation.
98
DAIRY
P. s/~1/alu:s {IOO-t99m.rn..l
N•32
D
H"'.49·±.37t
P. stellatus {2:00-2S9m. :n)
II]
N•27
.H=.ar ±.357
P. veJulus
N= 52.
H= .as± .466
r--
-~~
C.sligmoeu s
N= 65·
ii·.53 ± .347
1--:
+ + + + + +
.2.0 .40 .SO .80 LOO 1.20 l40 1.60 I.BO
~
~
0
40
40
+
+
OCEAN
P. slella/us (200 +m.mJ ·
BRIDGE
30
'
·11-,
-
30
N= 28
P.llellolutt (I00-t99m.ml
H•l7
20
-:::s-,
D
H•.43 ±.3s7
H:.s 3 ± .435
20
rn
(.!)
P. stella/us {200-299rn.mJ
0
N•53
....
0
~
"'E
D
H.• .36±.376
0
20~·
·
P..efulus
N=43
30
.c
::l 20
z
-"'
<=
N::lf2
10
30
~
"'
1:~455
H.:~.BS±-431
0
Q_
'
C.
0
N,97
20
H=.st ± .4oa
C. stigmat!us
20
N= 177
H"'.75±A34
10
stigmoeus
tO
oL-L-L-L-l-l-~i-------­
+ + + + + + + + + +
oL-L-L-l-l-~~~J=~---
++++++++++
0
.20 .40 .60 .BO 1.00 L20 1.40 L60 LBO
Trophic Diversity in a Single Gut (H)
0
.20 :40 _60 .80 LOO l20 l40 L60 lBO
Trophic Diversity in a Single GL~ (H)
99
Figure 15.
Frequency histograms of individual trophic
diversity for Psettichthys melanostictus at the-Ocean
station.
food.
1
H
N = the number of fish examined which-contained
= the
mean Brillouin trophic diversity in
individual guts ~ one standard deviatio~.
100
OCEAN
70,_
P me!anostictus ( :5150 m.m.)
(/') 6 0
-¢=::J
"-."-
0
-
H= .30
50
!.-
i
_Q 4 0:::J
E
b.
N::iJ6
-
-
-H= .12 ± .196
3 0-
r;;.
"""""
Q)
(.)
± .310
P.1me!anostictus (>150 m.m.>
@
z
D
N=39
(!)
:~~tJ
i:::;:;::~
2 0-
(9
Q_
,_
10
0
+
+
+
+
+
+
0 .20 .40 .60 .80 1.00
Trophic DiversHy in a SinQie Gu7 (H)
101
Figure 16.
The relationships
bet,~een
the mean evenness
·component· (J) and· the-·mean richness component (H) of
trophic diversity for each flatfish category at the
Kirby Park and Dairy stations.
standard deviation.
The bars indicate one
·.;·.,,
I
1.00
IT
.80
.60
KIRBY
PAR~{
r~
ll
J
102
.40
P. stellatus ( =:: 9 9 m.m.)
P. stellatus (I00-199 m.m.) = 6
.20
=o
P. velulus
0
~--~----~----~----~----~----~--~
-
1.00
.80
J
=o
.• TT
.•
I
.6
•
•
I
--{>
•
1 61
.40
•
.
I
l
DAIRY
-,
.
'
P. stellatus (I00-199 m.m.) = 6
P. stellatus (200-299rn.m.) = o
.20
0
P.vetulus
= 0
C stigmaeus
= e:.
~---.-----.----~----------~----~----·
.20
.40
.80
.60
H
1.00
1.20
1.40
103
Figure 17.
The relationships between the mean evenness
component (J) and the mean .richness component (H) of
individual trophic diversity_for each flatfish category
at the Bridge and Ocean stations.
one standard deviation.
The bars indicate
104
1.00-
BRIDGE
.80-
I
•
f--
J
.60-
-
t;.-
I
l1
6
1
•
0
I
.40-
= e;
( 200-299m.m.) = o
=0
P. stellatus (I00-199m.m.)
P stellatus
.20-
P.vetulus
C. stigmaeus = c.
0
1.00
I
I
J
.60
I
I j, 1
f]
.80
I
I
II
•
I
1
I
OCEAN
I if~
"I
1
'1
.4
.20
I
P stellatus (200+ m.m.)
Pvetulus
=0
C. stigmoeus = A
P. melanostictus ( ~ 150 m.m.)
= €9
= 0
0 L-----.-----.-~P._.~m~e~m~n~o~st~i~ctru~s__(~>-+!5~0~m~.m~.~)___=__o1 1_
.20
0
1.0 0
I. 20
1.40
.40
.60
.80
H
105
Figure 18,
Diagram of the relative abundance of the 10
most numerous items ·i:n the environment as measured by
benthic cores (% P), the relative abundance of the 10
most numerous prey items in the diets of each flatfish
category(% R), Electivity (E), and the Percent Similarity
Index value (% SI) bet,veen the relative composition of all
the items in the benthic cores and in the diets of each
flatfish category for Platichthys stellatus, Parouhrys
vetulus and Citharichthys stigmaeus at each station.
See Apuendix A for list of prey category codes.
DAIRY
KIRBY PARK
P. $/II/lOIIlS
( :S 99 m.m.l
%51•2.7
•;..P
%R
!l•l~
"
"
Ill•.'
ccap
,..
I
COlO
(
Eta~
Pool
'
~~0~~
II
j!,ono
,~,
Co<o
·~·
Goma
(/
""
"'"
Car a
I
~.:
,,.
Noml
J>.ono. ~·-,.-W--,.--;:
•1.00
U>O
0
•J.OO
"0
0
OIIQ
t./ftOI
Acal
/
1/
Abfl
Abrl
eolp
1'•00
Toll
Ada.
Copr
Han
A~ol
~~fl
Coro
Ceop
(
E
ct_,-~,-~
0
E
OCEAN
BRIDGE
P,.!f/11/(J/US (1QQ-[99m.m)
I" ,,,o
ro
0
4
Ur•
5olp 4 1"4
40
~"'-~
...
\1
IIi•
Glyl
Sill
I
!loip
Di•
"""
A~o
Cr.cp
·:_)
Poly
SQIO
I•
~~~.......
/
,...,•
l
I
,.
Mact
"'"'
Nlon
1
Hlml
1
""
Sbtn
141rTII
j
Ctd
\
CJCI
i
"'
•••
d'
!
'
rl'1
"·ibo '
0'
E
•. bo
""
At a\
Cron
Sblft
Aco\
),I nO I
Sb•n
Abrt
Qll 9
0
E
,oo
(
0
·L
E
w
~
0
''"
Cmm;
""'!
Pl!o
!hie
Abll
,~,
·~·
Pl(ll
,__..!:
-~.oo
1.00
o
E
''"I
Pdob
Me<~l
-.be
(
J
"',,...." I
Tmod
~
-1.00
I
'
0
E
Alrl
r
,.... IL
t.~ooc
0
E
'"
PiM
'"'
~I
I'IPI
··~
Eabl
.... I
SlhO
Pno
N1l1
l
Mopl
Hill
ldaot
... (
Euph
Plro
~COl
sl\!
)lCop
Sbln
PpfQ
Pho
"'o)\_o
0
Adn
)
...
5~10
EDn?
'kP
'?_
"'
··~
Tnui
'"' I
I
0
Pt.>lyd
Cryp
~
"""
Phto"
t.~oct
/
0
~
""
9
.....
+ ' ""' .."'•~C ,),
O"•C!O '
~or
%R
Tmod ( ..
Nt•n
Ceo~
•kP
Noll
Cytl
Cytl
""" ,;,,
r' .
~f&l
.,
I
J
'"'
Cap\
Abll
Sbon
f't,"'
Qom
'""" (
\
'""
0
,,.
"""
Cirri
).lOCI
Mocl
I
E991
"'~
zo
I
I
Ceo!
EgQI
Sn(Sl
Glyt
~··
EO ~0 ZO
BllP'-It-1-/P-
z•
'""'
"''
"/.51• 29
... p
%R
"!o51•2.4
%R
%P
"!oS\•41
'/. R
•,<,p
I
P.v111ulus
R Sllllla/US (200-299m.m.)
C.sNgmtMIJ$
%51• 9
P. vetullls
•JaSI• 2.5
"faA
"'oP
P.ilsllofus (200+m.m.l
%51• 8
C.stlgmaous
%51•16
%R
%P
>00
0
-1.00
E
t.OO
E
E
0
""'"
.,, --"-'
Crcl
c~ap
·1.00
1.00
0
·1.00
) '"...
"'"
,,.
EM~
E
E
'"'""'
Nlln
""
)
...
SnlSl
Mnol
Pilo
01!~ '~'-r-~--r~
Poly
'"'
'"" i
I
I
Hcop
Nttn
·~·
0\1;
Goma\
llllp -'i
Ho"
""
'"'
'"'
Sbln
0/r..R
60 20
~"
""',..,
c~ap
Pool
I
""
--"If"-
0/r..P
%R
'"0
Sn\51-'-f t-L-
,~·
Abfl
J
'
..'""
B1lp
Abit
c~a~
•t,p
1!l~ma,;1
%51•12.
%P
'"loR
%81•17
•,.!.51• 3
'/. p
!hip
\
Tn~t
Sbo~
"
I
'
Myld
0
,,
"'~
I
'
Tn(!;)
"'
'"
"/a5[•33
%A
%P
"''T
Ma~
j!,biC
P, VIIIU/US
P stsllolus (IOO~I99mml
%51•39
•;.p
%R
C.
P. rstulus
P. stllllolus (200-2.99)
P.sflll/otus {I00-199m.m.)
"loSI•IS
>.00
....
0
0'\
,
Ecol
I'Owb '
•IDO
0
E
.
100
.
107
Figure 19,
Diagram of the relative abundance of the 10
most numerous i terns in the environment -as --measured by
benthic .. cores (% P), the relative abundance of the 10 most
numerous prey items in the diets of each flatfish category
(% R), Electivity (E), and the Percent Similarity Index
value (%S.I,) between the relative composition of all the
items in the benthic cores and in the diets of each
flatfish category for Psettichthys melanostictus at the
Ocean station.
codes.
j
See Appendix A for list of prey category
108
P.melonosticlus (~ 150 m.m.)
P.melanostictus (> 150m.m.)
%SI=O
%SI=O
%P
20
0
20
%P
%R
I
'----r---'o-lj '
Melo
Nkad
Aeon·
Gran
Cnut
Cane
Poly
Atri
Aseu
Nele •....-----
.
I
Eear j
Ppyg j
Meal j
Pepi
i
Esen
j
i
i
i
i
i
i
i
i
~----·
Pmel
Gran
Pvet
Aeon
Begg
Cnig
Bath
Ophi
Nele •.------
Ppyg
Meal
Pepi
Esen
1
j
j
j
j
j
T~odj
Msae
j
j
Eobl
Eobl
Pdub •.--'---1---'---r--.
1.00
0
-1.00
E
1
Em or
Eear
Tmodj
•
20
Pisc
Adav
Msae
20
60
%R
0
j
j
Pdub •,-----'L--.,---'---r-~
-1.00
0
E
1.00
APPENDIX
109
ll
110
Table A.
List of prey category codes used in Figures 12-13
and 18-19.
Prey
Aang
Ab.:c
Abre
Acan
Acol
Adav
AI g
Ascu
Atri
Bath
Begg
Biv
Brae
Cat~cories
Allorchestes angusta
At:"or..on Ta becc~r i i
Ar~ndl9 brevis
Acanthomysis sp.
Aoroides columbiae
Acanthcmysls davisii
Algae
AcanthO""ysis sculpta
Atylus tridens
Bath~edon sp.
Brachiuran eggs
Bivalvia
Cane
Capi
Gapr
Ccal
Ccap
B;.achiopoda
Bivalve siphons
Cancer sp.
Capitellidae
Capretta sp.
CapreJia callfornica
Capite! ra capitata
Cirr
Cirripedia cirri
Dnag
Cnig
Cnut
Core
Cancer mag ish:r.
Crangon nigro~aculata
-CI inocardium nuttall i i
Corophium Si).
Bsip
:sp.
Cran
Crangon
Cryp
Cycl
Cypr
Oexc
Cryptor:~ya
Dig
Eana
Ecar
Eggs
Elou
Emor
Eobl
Epug
Esen
Ete
Euoh
G~
ca f i fern ica
Cyclaspis sp.
Cirripedia cypris larvae
Dendraster excentricus
Digested material
. Emerita ana toga
Euphi fomcdes carchcrodonta
Crustacean eggs
Exasond fourei
Engraul is mordax
Euphi lc::r.edes oblonga
Epine!!al ia pugetTC!nsis
Eohaus+orius senci !Ius
E7eone SiJ.
Euphi lcr..~..!as sp.
Ger.T."aric!~=
C~d
Ge=n.2:
Glyc
Glyc:era sp.
robusta
Harpadicoid cope;:od
Her.~igra;JSUS or:;vnensis
lcmprops sp.
Hedicr.-..astus cal ifornica
M.:'!c:l~ sp.
Grab
Hcop
Hare
larn
Meal
Mac
g~.!
Glyc~:-a
Hioher Ta:xon
Mact
c
Mel a
"Mnas
Mono
Msac
Pr
p
c
c
c
Mspi
Myid
c
Mysi
Nele
Neme
c
c
c
Nlo>d
M
Nten
Nvir
H
Ollg
c
c
On up
p
Ophi ·
Pbic
Pdab
Pegg
c
c
p
c
c
Pepi
Pfra
c
Phor
Pisc
Pinn
PI ig
H
c
c
Pmt!l
H
Pobt
c
c
Poly
Polyd
Ed
Polyn
Ppau
C
C
C
P
Ppyg
Po;t
Pvet
Pi
Sben
C
C.
C
p
C
C
M
P
Sgra
Si I i
Terc
p
Trr.cd
C
Tnut
Tn<SJ
Tse2
Sn(S)
Spio
Ssho
Ssic
Syn
C
C
P
Ure
Mactridae
Metamysidapsis elongata
Macoma nasuta
Monoculaides sp.
Megelona saccu lata
Manoculoides spinipes
Myidae
Mysidae
Nothri a e I egan s
Nemertlne.':l
Neorr.ysis kadiakensis
Not~astus tenuis
Neanthes virens
M
C
M
C
P
C
M
C
P
C
P
P
Ollgochae~a
Onuphidae
Ophiuroidca
Platynereis biCa.ndliculata
ParaphoJ<:us dabOius
Pisces eggs
Paraphoxus epist~us
Pinnixa franciscana
Phoronidea
Pisces
Pinnixa sp.
PolyC:ora I igni
Psettichthys melanostic-fus
Paraphox~s obtusidense
Polychaeta
Palydora sp.
Polynoidee
Pol ydora paucibrachiata
Priospio pygr.~a.;!:.JS
Podocopid ostr=cad
Parophrys vetulus
Streblospio benedicti
Scleroplax granulata
Siliqua sp.
Saxidcrnus nuttall i siphons
Spianidee
Synch.::l idium shaer.~keri
Solen sicarius
Synchel idiur.~ sp.
.., Tercbellidae
Tell ina mode:;ta
Tresus nutted iii
Tresus nuttallii siphons
Tcrr~strial
P
Ed
P
C
Pi
C
C
Pi
C
P
PI
C
P
P
P
P
P
C
Pi
P
C
M
M
P
C
M
C
P
M
M
M
seeJs
Urechi s c::~upo
E
M
_ _=::__:~----------------------
Pr- ==
E
P
-=
Protozoa
Ech iura i C:e~
P.:llychaeta
c
H
Crustacea
!o'ollusca
PI
Pisc.;;;
Ed
Echi01c.!~:-c·,:t~
111
Table -B. Index of Relative Importance (IRI) summary for the Kirby
Park station. %N = percent numerical composition, %V = oercent
volumetric composition, %LO. = percent frequency of occurrence
Platlc:htn!(! stellatllS
PI"'IO"""'
FDf'-tnll•ra h.,l,...t,l
........., •• boccarll
(IFtlldh..., go.nlarl
-rt-
11,00
O.)l
\l,l)- 111.11
6
" --rt ... fo.ntdent.l
Ec:llllli"'I.-.
•
Un~chll """'"'
AnMIIda
,_,
,_,.
t101J-I~1
'-"'
'·"'
""
,_, "-"'
,_,
"
,_., '·"'
0.91
0.011
0.01
1.20
o.o«s
t.lll
],98
l.ll
0.69
0.]2
u.oo
4.00
. o.oo
o.y;
e.oo
2.00
0.07
b.og,.....,.,.,,...,
;~
f
'
Splcntd- (...,[dent. I
o.n ,_,.
'·"
"
'-"' '·" ,_,. ""'-'
"
O,l5
O.ll
6.66
4.~
II
0.60
0.5]
l'J.IIl 22.20
6.66
eo.oo
6.26
10
C96l.na
2
--
ost~
(..,[.s.nt.l
0.15
1.01
'·"
0."
0. Ill
9.48
2.]2
0.19
o.n
v.n ·
'·"'
'""..,..,.
......-..
Ostnu:oda
Pod<x:c>pld
l'6..ll
9.61
0.16
11.18
0.14
2.~
].,1
0.62
5.60
1.20
1.20
1.20
2 • .0
211.91
~n.96
2.10
2.((1
II.Qil;
0.49
0.20
20.00
15.96
•
0.09
0.111
0.07
o."
2.•o
0.]1
1.20
5.01 - 2:2.!19
o.zz . 1.%0
I.U
1.20
""·'
'·"
'·" ""•
·-~
.......,..
1-ropiiiS ...,..,.,...,_sla
sp.
0.26
20.00
42.19
5.26 _5l~ll
n1.S9
Mphlp<><1a
Atlof"d>oostu ang111ta
,.,..,Ides o:~t...ot ..
~tr.l~sp~.
10,]1
Oaarpoclli
Can<::ar sp.
.....,, ....,pS<~S
9
In :act.
~nata
_
Tar .... atrhl lnS*Cfs lunlddnt.l
T•r,...strt .. In~ Ia ......
~[IU$C8
at ... l,.la
.......
Bt ..... l - alptcu
lobdlntus S!l·
. """''
0.211
"
1.5l
"
'-"'
o.u
11.1111
10.06
61.«
1TI6.6l
1.75
7.14
111.07
111.]5
.M.I!Z
111.)0
111.95
2.40
1..20
1.71]
5.22
..
"'",
""
:.t.ll
1.15
1.55
].'ill
0.1•
o.21
,...,t.s.nt.l
C..pNotasplda (.-.ldent.J
,_,
1.23
0.91
2.11
5.[1.1
62.00
2.00
26.00
12.00
)"..21
'· I•
1.1!0
1.21
lfi.OO
2.00
'il.•l
112.110
,_,
12.19
'-"'
],61
].61
4.111
,_,
'-"'
'"''-"
'
5.12
"•
'
"90.1&
""
11.1!2
o.M
o.r.~
ta.oo
19.ao
15.11
4,26
10.00
19<1.30
1.J1
o.4ti
•.oo
1.<tO
5.32
l • .lll
)o(.IJU
221.110
1.411
0.'-2 10.00
10.00
6.•..!!0_ . ..J.l.Q._~ •19.!_6
1.14
o.:s:z
2.00
2.!ll
10.16
O.ll
t.Ol
1.~
6'1.00
O.Z'il
0.11
~.00
11-'9-20
2.4a
6.96
•
•.oo
.
Fish eggs (unlclont.l
•ctsc.tt .........,.
0.111
Tar,...strl•l s.aads
o.oo
51.20 100.00 5120.00
l5!i .
Tot,. I Nurober ol Prey Cet•gorl•s
N....O.r <>I Fish u.-ln•d h<lth cont.,hl
"
"
'-""
"-"'
o.09
3.61
o.n
5. n 49.l9 21).1..911
29. II llO. 36 26,UJ!1
..
'"'
"
"•
'
"
"
"•
,._,
,
""
"
11.11<'
49.!19
0.611
0.12
2.91
0.32
16.08
25.!19
2.00
"
2.00
6.511
•• 00
64.32
1!2.00 2122.911
""
2.00
0.21
Yal""f"obn~1lo
7
111.54
1011.]6
'·" '·" "
"""
,_,
,_
'-""
""
•-«
,_,.
'·"
o.u '-" '·"'
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Goat~
Hooogast~
.aterlal
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1.26
2.16
lolo.c:c-e SliP•
14yldoe ..... tc~ont.l
Cllnoo::ardt ... nun.! lit
OI~rt·d
3.61
6.211
-4.111
6.~9
50.60. ·~D.A~
0.45
1.0
,_,
,_,.
,_,.
t..,tdent.J
nu""tlll
r.-. .... s nuTtallll slphc:ns
"-
,_,.
'-""
21.49
·-~
14ooctrl~
r .... s.,s
'
4.00
16.00
2.12
,_
'·"
,_,
'·" '·"'
0.01
1.111
•.oo
1.6l
].60
].46
"
,_, "
""
11.110
n
n
1.95
0.16
l lll.,.cflc:olda (..,lde<!t.l
C,Cia~h
10.91
0.13
Poly<bra sp.
Prl ........ pl<> sp.
Pseud<>p<>ly~ pauc::lbranclllat.
st .... btospl<> r.-<11<:1"1
flepftlyil t:omuh f.-....::[$Cana
Clrntull.,.._ (~nld-oont.l
A.--nd!a b,..,.[a
Cal)lt•llldaa IU1ldant.l
-Qrp In !Ia ao;ttft"te
N<>"h:>ooastus t ...... !s
16.1!6
"
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Qllgodle•ho
Pol yd'>oet•
Polyc:hM-111 lo.nldent.)
Pltytln6o<:ldae (o.nl,...t.l
Etecn• ~[f..,... 1""0" ,..l[fomtc:.o.
.[..,.Ida J.P•
E.... tu bil<>llah
""'
,_, "
9.U
6.5]
].311
o.oo
0.00
"
"
'
112
Table C. Index of ~elative Imoortance (IRI) summary for the Dairy
station. %N = percent num~rical composition, %V =percent volumetric
composition, %F.O. = percent frequency of occurrence
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1.1!
I.U ,1,11 111.!11
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Index of Relative Importance (IRI) summary for the Ocean
Table
station. %N = percent numerical composition, %V = percent volumetric
composition, %F.O. = percent frequency of occurrence
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I
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