Feeding of capelin (Mallotus villosus) in Newfoundland waters
Richard L. O’Driscoll, Morag J.D. Parsons & George A. Rose
SARSIA
O’Driscoll RL, Parsons MJD, Rose GA. 2001. Feeding of capelin (Mallotus villosus) in Newfoundland waters. Sarsia 86:165-176.
The diet of capelin (Mallotus villosus Müller) from six areas off the Newfoundland and Labrador
coast was compared over three seasons (January, May-June, August-September) in 1999. A total of
1247 stomachs were examined. Of these, 837 (67 %) contained food. The proportion of empty stomachs was higher in winter (55 %) than in spring (28 %) or autumn (20 %). Copepods were the major
prey over all areas and seasons, occurring in 90 % of non-empty stomachs. Hyperiid amphipods,
euphausiids, larvaceans and chaetognaths were also important, occurring in 30 %, 11 %, 9 % and 7 %
of non-empty stomachs respectively. The importance of these other prey groups increased with increasing capelin size. Larger capelin contained larger prey. There were also spatial and temporal
differences in diet. Capelin from Placentia Bay, southeastern Newfoundland, consumed smaller
copepods and a higher proportion of amphipods than capelin from other areas. Diet composition,
particularly the incidence of lipid-rich Calanus species, may influence capelin growth.
Richard L. O’Driscoll*, Morag J.D. Parsons, & George A. Rose, Fisheries Conservation, Fisheries and
Marine Institute, Memorial University of Newfoundland, P.O. Box 4920, St. John’s NF, Canada A1C 5R3.
*Present address: National Institute of Water and Atmospheric Research (NIWA), PO Box 14-901,
Kilbirnie, Wellington, New Zealand.
E-mail: [email protected]
Keywords: Capelin; Mallotus villosus; diet; feeding; growth; Newfoundland.
INTRODUCTION
Capelin (Mallotus villosus Müller) are an important
component of many northern marine ecosystems. In
waters off Newfoundland and Labrador capelin are a
key forage species for many species of marine mammals (e.g. humpback whale Megaptera novaeangliae
Borowski, harp seal Phoca groenlandica Fabricius),
seabirds (e.g. murres Uria spp., Atlantic puffin Fratercula arctica L.) and fish (e.g. Atlantic cod Gadus
morhua L., Greenland halibut Reinhardtius hippoglossoides Walbaum), as well as supporting a moderate (quota ~30 000 tons in 1999) commercial fishery.
Despite their central role as a link between zooplankton production and higher trophic levels (Bundy
& al. 2000), relatively little is known about feeding of
capelin in the Northwest Atlantic. Several studies
(Templeman 1948; Kovalyov & Kudrin 1973; Chan &
Carscadden 1976; Marchand & al. 1999) describe
capelin diet in general terms, but only Vesin & al. (1981)
and Gerasimova (1994) provide quantitative accounts
of prey composition across a range of capelin sizes.
These two studies were restricted spatially (western Gulf
of St. Lawrence, Vesin & al. 1981; Grand Banks,
Gerasimova 1994) and the work of Gerasimova (1994)
was only in the spring (April-May).
In this paper we present information on capelin diet
over a broad geographical area and across three sea-
sons. This is the most extensive quantitative account of
the diet of capelin from Newfoundland waters to date.
Such information is important for understanding the role
of capelin in the Northwest Atlantic ecosystem and allows comparison with recent feeding studies from other
northern regions (e.g. Iceland, Astthorsson & Gislason
1997; Barents Sea, Ajiad & Pushchaeva 1992; Bering
Sea, Naumenko 1984).
MATERIAL AND METHODS
SAMPLE COLLECTION
Capelin were sampled using either a Campelen 1800
bottom-trawl or an International Young Gadoids Pelagic
Trawl (IYGPT) mid-water-trawl during acoustic-trawl
research surveys in winter (January), spring (May-June)
and autumn (August-September) 1999. Both trawls
were fitted with a cod-end liner with a mesh size of 13
mm. Fishing times were between 15-30 min. Tow depth
ranged from near surface (~20 m) to 300 m.
Samples were collected at sites across the Northeast
Newfoundland and Labrador Shelf and within major
bays on the northeast and southeast coast (Fig. 1). Six
key areas were identified corresponding to the location
of acoustically detected concentrations of capelin (Fig.
1). Two areas (Northeast Grand Bank and Labrador)
were sampled in all three seasons, two areas (Trinity
Bay and Placentia Bay) were sampled in winter and
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Sarsia 86:165-176 – 2001
Fig. 1. Location of trawl stations where capelin samples were
collected in winter (squares), spring (circles) and autumn
(stars) 1999. Six key areas are indicated.
spring only, and the remaining two areas (Avalon Peninsula and Funk Island Bank) were only sampled in
one season (spring and autumn respectively). Samples
from four other sites outside these key areas were also
examined (Fig. 1).
A random sample of 200 capelin was measured from
each trawl. From this sample a subsample of up to five
fish per 10-mm length class was selected for stomach
analysis. Because of spatial differences in length composition of catches, it was seldom possible to obtain
five fish from each available length class in every catch.
In winter and autumn, the abdominal wall of each
capelin selected for stomach analysis was slit and then
the whole fish was preserved in 4 % formaldehydeseawater solution for later dissection and analysis. In
spring, stomachs of selected fish were dissected at sea
and preserved in 4 % formaldehyde-seawater solution.
A further subsample of up to five fish per 10-mm length
class from each trawl was frozen for subsequent otolith
removal and ageing.
SAMPLE ANALYSIS
Total length, weight, sex, maturity and stomach fullness (on a scale of 0-4 where 0 is empty and 4 is full,
Chan & Carscadden 1976) were assessed for all subsampled capelin (i.e. up to ten fish per 10-mm length
class). Where appropriate total length (from tip of the
mandible to the end of the ventral lobe of the tail) was
corrected for shrinkage during preservation or freezing. Thawed lengths of frozen fish were converted to
fresh lengths by multiplying by a factor of 1.03 (Winters 1982). Lengths of whole fish preserved in formalin
where multiplied by a factor of 1.05 (our unpublished
data).
Stomach contents from formaldehyde-preserved samples were washed and then examined under a dissecting microscope. Contents were sorted into major taxonomic groups (usually class or order, e.g. copepods,
amphipods, euphausiids, larvaceans, pteropods, chaetognaths, fish larvae, etc) and counted. The prey group
that contributed the greatest volume of the diet (measured by displacement) of each individual was noted.
Weights of stomach contents were not recorded because
a suitably sensitive balance was not available. Intact
prey items were measured to the nearest 0.1 mm. Total
lengths were measured for all groups except copepods
where prosome length was measured. It was impossible to obtain sizes for some groups (e.g. larvaceans,
pteropods) because of digestion and distortion. When
more than 50 intact copepods were present in the stomach a random sample of 50 was selected and measured.
Approximately 10 % of stomach samples were selected based on the prey composition and degree of digestion (only relatively undigested samples were selected) for more detailed identification. In these samples, prey items were identified to the lowest possible
taxonomic level (usually genera). The range of sizes of
each taxon present in the stomach contents was recorded.
STATISTICAL ANALYSIS
It was difficult to formally compare capelin diet between
seasons and locations because of differences in the size
of fish from different areas. Differences in capelin size
will confound seasonal and spatial patterns because of
length related selectivity of prey (see Results).
We used diet information from all samples combined
and observed length frequency distributions to calculate the expected proportion of stomachs from each area/
season containing a prey group. For example, over all
areas 30 % of non-empty stomachs from capelin 130139 mm in length contained hyperiid amphipods. Fourteen capelin with non-empty stomachs from Trinity Bay
spring samples were in this length range. If diet was
similar over all areas and locations we would expect
0.3(14) = 4 capelin in the 130-139 mm length class from
Trinity Bay spring samples to contain hyperiids. Mathematically, expected occurrence of prey group f in area
a and season s, Efsa was calculated as:
x
E fsa = - p fi nasi
i =1
Where pfi was the overall proportion of stomachs in 10
mm length class i (i = 1,2,3 … x) that contain prey group
f and nasi was the number of capelin samples from fish
in length class i from area a and season s. The pfi was
O’Driscoll – Capelin feeding
expressed as a proportion of non-empty stomachs except for empty stomachs (pempty,i) where it was the proportion of total stomachs in length class i.
Expected values of prey occurrence Efsa were compared to observed values using a two-sided binomial
test of proportions (Freund 1988). The null hypothesis
that diet was similar over all areas and seasons was rejected if a prey group was observed significantly more
or less frequently than expected. The test assumes that
individual capelin stomachs were statistically independent samples. This assumption may be violated where
capelin were taken from the same trawl catch, so pvalues should be treated with caution.
To examine seasonal and spatial variation in the size
composition of copepods in capelin diet, copepod sizes
were first standardised by capelin length. A linear regression was fitted to a plot of log-transformed copepod
prosome lengths as a function of log-transformed
capelin length. Residuals about this fitted regression
provided a standardised measure of copepod size independent of capelin length. Non-parametric Mann
Whitney and Kruskal Wallis tests (Freund 1988) were
then used to compare standardised copepod sizes between areas and seasons. Kruskal Wallis tests were also
used to compare the size (length-at-age) of capelin between areas.
RESULTS
DIET COMPOSITION
A total of 1247 stomachs from 48 trawl samples were
examined (Table 1). Of these 837 (67 %) contained food.
Copepods were the dominant prey over all capelin
lengths, sites and seasons, occurring in 90 % of nonempty stomachs and being the major prey by volume in
69 % of non-empty stomachs (Table 2). The most common genera of copepods identified from a subset of
capelin stomachs were Calanus, Metridia, and Temora
(Table 3). Hyperiid amphipods (Themisto spp.),
euphausiids (Thysanoessa spp.), larvaceans (Oikopleura
sp.) and chaetognaths (Sagitta sp.) were also important
in capelin diet, occurring in 30 %, 11 %, 9 % and 7 %
of non-empty stomachs respectively (Table 2). Several
other groups were present in a small proportion (< 5 %)
of stomachs (Tables 2-3).
LENGTH RELATED SELECTIVITY OF PREY
Capelin lengths ranged from 72-193 mm. There was
strong evidence for differences in selectivity of prey
related to capelin length (Fig. 2). Larger prey items such
as hyperiid amphipods, mysids, larvaceans, pteropods
and fish larvae occurred more frequently in the stomachs of larger capelin. Smaller prey like molluscan larvae, fish eggs and diatoms were eaten by smaller
capelin. Copepods and euphausiids were consumed by
all lengths of capelin (Fig. 2). Both copepods and
euphausiids occurred in a wide range of sizes in the
diet (Table 3) due to the presence of different species of
copepods and different developmental stages of copepods and euphausiids. There was also evidence for selection within prey groups, with larger capelin eating
larger individuals. This selectivity was particularly clear
for copepods (Fig. 3).
SEASONAL AND SPATIAL DIFFERENCES IN DIET
There were spatial and seasonal differences in capelin
diet (Fig. 4). In general the proportion of empty stomachs was lower in spring (28 %) and autumn (20 %)
than in winter (55 %), but in some areas (Labrador and
Table 2. Frequency of occurrence and importance of prey
groups from the stomachs of capelin caught in Newfoundland
waters in winter, spring and autumn 1999. Occurrence is the
number of non-empty stomachs that contained a prey group.
Dominance is the number of stomachs in which the prey group
contributed the highest volume of stomach contents. Total
number of stomachs examined (Table 1) was 1247.
Prey Group
Table 1. Summary of samples used to examine seasonal and
spatial differences in capelin diet in Newfoundland waters.
First number in each cell is the number of individual stomachs analysed. Second number (in parentheses) is the number
of trawl sets from which stomach samples were taken. Area
locations are shown in Fig. 1.
Winter
Labrador
Funk Island Bank
Trinity Bay
Avalon Peninsula
Northeast Grand Banks
Placentia Bay
Other
70
0
31
0
63
107
37
(9)
(1)
(2)
(3)
(1)
Spring
102
0
126
55
90
298
0
(3)
(4)
(2)
(3)
(11)
Autumn
90
90
0
0
29
0
59
(2)
(3)
(1)
(3)
167
Copepods
Hyperiid Amphipods
Euphausiids
Larvaceans
Chaetognaths
Molluscan larvae
Pteropods
Fish larvae
Cirripedian larvae
Mysids
Brachyuran larvae
Cladocerans
Fish eggs
Diatoms
Empty
Occurrence
Dominance
753
248
95
79
61
42
33
21
19
15
8
7
7
6
410
578
145
42
31
9
0
7
14
0
5
0
2
0
0
410
168
Sarsia 86:165-176 – 2001
Northeast Grand Banks) the level of feeding remained
low (> 50 % of stomachs empty) in spring. Copepods
were an important prey in all areas and all seasons, but
other groups contributed a higher volume of the diet at
specific times and locations. For example larvaceans
were the dominant prey in 49 % of capelin stomachs
from the Avalon Peninsula in spring (Fig. 4).
Table 4 compares expected values of prey occurrence
(Efsa) to observed values. Although significance levels
should be treated with caution because of the assump-
Table 3. Taxa identified from each of the prey groupings in
Table 2. The season (W = winter, S = spring, A = autumn) in
which each genera was recorded and range of sizes found in
capelin stomachs are also given.
Prey group
Copepods
Calanus spp.
Centropages sp.
Euchaeta sp.
Metridia sp.
Microcalanus sp.
Paracalanus sp.
Pseudocalanus sp.
Temora spp.
Hyperiid Amphipods
Themisto spp.
Euphausiids
Thysanoessa spp.
Cladocerans
Podon sp.
Mysids
Unidentified
Brachyuran larvae
Unidentified
Cirripedian larvae
Unidentified cyprids
Unidentified nauplii
Larvaceans
Oikopleura sp.
Pteropods
Limacina sp.
Molluscan larvae
Unidentified Prosobranchs
Unidentified Lamellibranch
Chaetognaths
Sagitta sp.
Fish larvae
Ammodytes sp.
Gadus morhua L.
Fish eggs
Unidentified
Diatoms
Unidentified
Season
Size range (mm)
W,S,A
A
S
W,S,A
S
S
S,A
W,S,A
1.5-7.2*
0.8-1.0*
1.0-2.7*
0.5-0.9*
0.9-1.2*
0.6-2.0*
0.5-1.1*
W,S,A
1.5-18.2
W,S,A
1.7-27.3
A
0.8-1.1
W,S
5.5-22.6
S,A
-
W,S
S
0.4-0.5
S
-
S,A
-
W,S,A
A
0.2-0.6
0.2
W,S,A
19.0-30.0
S
S
32.4-46.9
12.2-20.0
S,A
-
W,S,A
0.1-0.2
*Copepod lengths are prosome lengths only. Lengths of all
other prey items are total lengths.
tion of independent samples (see Material and Methods), Table 4 provides useful information about spatial
and seasonal variation in diet taking into account differences in capelin size. For example, capelin from
Labrador in winter had a relatively high proportion of
empty stomachs (Table 4). In non-empty stomachs the
occurrence of copepods and larvaceans in Labrador
winter samples was lower than expected, while the proportion containing euphausiids was higher than expected
(Table 4). In contrast, capelin from the Avalon Peninsula in spring had lower proportions of empty stomachs and stomachs containing euphausiids than expected, but relatively high occurrence of copepods,
larvaceans and pteropods (Table 4).
There was also seasonal and spatial variation in the
size composition of copepods in capelin stomachs. Figure 5 shows the linear regression between log-transformed copepod prosome lengths and log-transformed
capelin lengths used to standardise copepod size and
account for length related selectivity (Fig. 3). Residuals
about this fitted regression were used to examine seasonal and spatial patterns in copepod size independent
of differences in capelin length (Fig. 6).
In the two areas which were sampled in all three seasons (Labrador and Northeast Grand Banks) there were
significant seasonal differences in the size of copepods
in capelin stomachs (Kruskal Wallis tests: Labrador, χ2 =
9.2, d.f = 2, p = 0.01; Northeast Grand Banks, χ2 = 14.0,
d.f = 2, p = 0.001). The decrease in the size of copepods
in capelin stomachs between winter and spring in these
two areas and also in Trinity Bay (Fig. 6) was largely
due to transition in the diet from large overwintering
Calanus spp. (copepodite V-VI) to smaller, earlier developmental stages (copepodite I-V) of the next Calanus
generation.
Capelin from Placentia Bay fed on smaller copepods
during the winter than capelin from other areas (Fig. 6,
Kruskal Wallis test, χ2 = 48.2, d.f = 3, p < 0.001). Examination of identified samples showed Temora spp.
and Metridia spp. were much more abundant than
Calanus spp. in the winter diet of Placentia Bay capelin.
The proportion of Calanus in the diet of capelin in
Placentia Bay increased in the spring, and this was reflected in the increased size of copepods observed in
stomachs in spring compared to winter (Fig. 6, Mann
Whitney U test, U = 924, Z = –5.56, p < 0.001). Despite the increase of importance of Calanus in spring,
the diet of capelin in Placentia Bay still consisted of
smaller copepods than in other areas (Fig. 6, Kruskal
Wallis test χ2 = 71.5, d.f = 4, p < 0.001). This was because few large Calanus (copepodite V) were observed
in capelin stomachs from Placentia Bay in spring and
there was a higher proportion of smaller species such
as Metridia, Temora and Pseudocalanus than in other
O’Driscoll – Capelin feeding
169
Fig. 2. Length related selectivity of prey groups by capelin. Length frequency
of capelin from which stomachs were analysed is shown in the top left panel.
Percentage occurrence of empty stomachs (second panel in left column) is
the proportion of all stomachs within a 10-mm length class that contained no
food. In all remaining panels percentage occurrence is the proportion of nonempty stomachs within a length class that contained a particular prey group.
areas. Perhaps because of the paucity of large copepods,
larger capelin from Placentia Bay fed mainly on hyperiid
amphipods in spring. Fifty six percent of non-empty
stomachs from large (> 140 mm) capelin sampled in
Placentia Bay in spring were dominated by amphipods
compared to 20 % of stomachs where copepods were
dominant. In other areas copepods remained important
for larger capelin. For example, in Trinity Bay in spring
copepods were the dominant item in 70 % of non-empty
stomachs from capelin > 140 mm.
SEASONAL AND SPATIAL DIFFERENCES IN CAPELIN SIZE
There were spatial differences in length-at-age of capelin
(Fig. 7). In all areas size of capelin increased between
winter and spring, consistent with growth (Fig. 7). In
winter capelin from Labrador were larger than fish from
Trinity Bay, Northeast Grand Banks and Placentia Bay
(Fig. 7). By the spring, capelin from Labrador, Trinity
Bay, Northeast Grand Banks and the Avalon Peninsula
were similar in length (Fig. 7), indicating more rapid
growth in Trinity Bay and the Northeast Grand Banks
than in Labrador or movement of larger fish into these
areas from the north. Capelin from Placentia Bay were
generally similar in size to fish from Trinity Bay and
the Northeast Grand Banks in winter, but were significantly smaller than capelin from all other areas in spring
(Fig. 7). Autumn age data are not presented because
sample sizes were small and it was difficult to separate
immature, maturing and recovering (spent) fish in autumn samples.
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Sarsia 86:165-176 – 2001
Fig. 3. Length related selectivity of copepods by capelin. Eight panels show percentage occurrence of eight 1-mm size classes
of copepods based on measurements of prosome length. Occurrence of each copepod size class is expressed as a percentage of
stomachs within a 10-mm capelin length class that contained copepods of any size (Fig. 2).
DISCUSSION
Diet composition of capelin from Newfoundland waters in 1999 was broadly similar to that reported in previous feeding studies in the Northwest Atlantic
(Templeman 1948; Kovalyov & Kudrin 1973; Chan &
Carscadden 1976; Vesin & al. 1981; Gerasimova 1994;
Marchand & al. 1999) and in other northern regions
(Naumenko 1984; Ajiad & Pushchaeva 1992; Huse &
Toresen 1996; Astthorsson & Gislason 1997). In this
study, as in previous work, the diet was dominated by
copepods particularly Calanus spp. Other groups were
also present including hyperiid amphipods, euphausiids,
larvaceans and chaetognaths. The contribution of these
other groups appears to increase with capelin size (Vesin
& al. 1981; Ajiad & Pushchaeva 1992; Gerasimova
1994; Huse & Toresen 1996; Astthorsson & Gislason
1997; this study) and may also vary interannually
(Gerasimova 1994), seasonally (Vesin & al. 1981;
Astthorsson & Gislason 1997; this study) and spatially
(Naumenko 1984; this study).
Euphausiids were less important in this study than
previously reported, occurring in only 11 % of nonempty capelin stomachs. This proportion was lower than
in earlier studies of capelin diet in Newfoundland waters. Kovalyov & Kudrin (1973) recorded euphausiids
in 44 % of stomachs with food in March-June 1972,
while Gerasimova (1994) found euphausiids in 11-28 %
of non-empty capelin stomachs from the Grand Banks
in April-May 1987-1990. In other areas euphausiids
seem to play an even more important role in capelin
diet, making up 80-90 % of the diet (by weight) in parts
O’Driscoll – Capelin feeding
171
Fig. 4. Seasonal and spatial differences in importance of major prey groupings from six areas in Newfoundland waters. Area
locations are shown in Fig. 1 and sample sizes are provided in Table 1. Missing bars indicate no samples were collected.
Percentage dominance is the proportion of stomachs in which the prey group contributed the highest volume of stomach contents.
of the Bering Sea (Naumenko 1984) and over 95 % of
the stomach content weight of large (12-14.9 cm) capelin in the Barents Sea (Ajiad & Puschaeva 1992). Conversely, hyperiid amphipods were a relatively important contributor to the diet of capelin in this study, occurring in 30 % of non-empty stomachs. This was similar to the proportion reported for capelin from New-
foundland waters by Kovalyov & Kudrin (1973), but
higher than previously observed on the Grand Banks
(5-15 % of non-empty stomachs, Gerasimova 1994) and
also higher than in other northern regions (e.g. Iceland,
Astthorsson & Gislason 1997).
Previous studies in Newfoundland waters (Templeman 1948; Kovalyov & Kudrin 1973; Gerasimova 1994)
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Sarsia 86:165-176 – 2001
Fig. 5. Relationship between log-transformed copepod length
and log-transformed capelin length.
have reported cannibalism of capelin eggs and larvae.
For example, Templeman found capelin eggs made up
~90 % of the diet of spawning and post-spawning
capelin sampled near-shore. No identifiable capelin eggs
or larvae were observed in capelin stomach contents
examined in this study. Cannibalism is probably only
important in spawning areas during or immediately following spawning.
The seasonality of capelin feeding observed in Newfoundland waters in 1999 was consistent with previous
reports (Chan & Carscadden 1976; Vesin & al. 1981;
Astthorsson & Gislason 1997). Levels of feeding were
lower in winter than in spring and autumn. The sea-
Fig. 6. Seasonal and spatial variation of copepod sizes in
capelin stomachs. Standardised copepod sizes are residuals
about the fitted regression in Fig. 5 and so are corrected for
capelin length selectivity. Boxes show 25th to 75th percentiles divided by the median. Whiskers show the range of sizes.
W = winter, S = spring and A = autumn.
sonal pattern in capelin feeding was probably related to
seasonal patterns in abundance of zooplankton prey.
Continuous plankton recorder (CPR) records from the
Table 4. Spatial and seasonal differences in composition of capelin diet in Newfoundland waters. Symbols indicate whether
occurrence of a prey group in capelin stomachs was higher (+), lower (–), or the same (0) as expected occurrence assuming
equal availability of prey across time and space. Expected occurrences were calculated based on overall size selectivity of prey
groups (Fig. 2) and observed length frequencies of capelin in each area and season. Significance levels were based on two-sided
binomial tests of probability (*** = p < 0.001, ** = p < 0.01, * = p < 0.05, NS = p > 0.05). There was no correction applied for
multiple tests.
Area
Season
Empty
Hyperiids
Copepods
Larvaceans
Molluscan ChaetoEuphausiids
Pteropods larvae
gnaths
Fish
larvae
Labrador
Winter
Spring
Autumn
+ ***
+ ***
– ***
– ***
+ NS
+*
– NS
+ NS
+ NS
+ ***
0 NS
+ NS
–*
–*
–*
– NS
+ ***
– NS
– NS
+ NS
– NS
– NS
– NS
– NS
– NS
0 NS
– NS
Funk Island
Bank
Autumn
– NS
+ NS
– **
– NS
– **
– NS
+ **
+ ***
– NS
Trinity Bay
Winter
Spring
+ ***
– NS
– **
+ ***
+ NS
– ***
– NS
+ NS
– NS
+ NS
0 NS
+ NS
– NS
– NS
– NS
–*
0 NS
+ NS
Avalon
Peninsula
Spring
– ***
+*
+ NS
– **
+ ***
+ ***
0 NS
– NS
– NS
NE Grand
Banks
Winter
Spring
Autumn
+ NS
+ ***
0 NS
+ NS
+ NS
+ NS
–*
– ***
+ ***
– NS
–*
+ **
– NS
+ NS
– NS
– NS
– NS
0 NS
– NS
0 NS
+ NS
+ **
0 NS
– NS
0 NS
– NS
0 NS
Placentia
Bay
Winter
Spring
+ ***
– ***
0 NS
– ***
– NS
+ ***
– NS
+ NS
– NS
– ***
0 NS
– ***
+ NS
–*
– NS
+*
0 NS
+ ***
O’Driscoll – Capelin feeding
Fig. 7. Spatial variation in mean length-at-age of capelin in Newfoundland waters in winter (January) and
spring (May-June). Error bars are + 2 SE. Plots are segregated by sex and maturity because there are differences
in size between these groupings (Winters 1982). LA = Labrador, TB = Trinity Bay, NG = Northeast Grand
Banks, AP = Avalon Peninsula, PB = Placentia Bay. Significance levels from non-parametric Kruskal Wallis
tests are shown in the upper right of each plot (*** = p < 0.001, ** = p < 0.01, * = p < 0.05, NS = p > 0.05).
173
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Sarsia 86:165-176 – 2001
Northwest Atlantic show most zooplankton species exhibit peak abundance in the spring or autumn, with
greatly reduced abundance during the winter (Myers &
al. 1994). The timing of seasonal cycles in zooplankton
abundance varies between regions (Myers & al. 1994).
The relatively low levels of capelin feeding we observed
off Labrador and on the Northeast Grand Banks in MayJune 1999 may reflect delayed development of zooplankton biomass in these regions relative to areas further inshore and to the south (Trinity Bay, Avalon Peninsula and Placentia Bay).
Temporal and spatial differences in capelin diet probably reflect the underlying composition of the zooplankton (Astthorsson & Gislason 1997). We did not
collect zooplankton samples, but most common zooplankton taxa reported from Newfoundland waters
(Strong 1981) were found in capelin stomachs. An exception was the cyclopoid copepods. Cyclopoids, particularly Oithona similis Claus, were relatively abundant in zooplankton samples collected over the Newfoundland Shelf (Strong 1981; Pepin & Maillet 2000)
but were not observed in capelin stomachs during this
study. Oithona similis were present in the diet of larval
(5-14 mm) capelin from Newfoundland waters (Pepin
& Penney 1997), suggesting that their absence in this
study may be related to the limited length range of fish
sampled.
The small size-at-age of capelin from Placentia Bay
and the relatively large size-at-age of capelin from Labrador contradict the earlier observations of Winters
(1982) that capelin growth increased with increasing
water temperature from north to south. Differences in
length-at-age between Placentia Bay capelin and capelin
from other regions may be related to spatial variation
in diet, particularly in the consumption of Calanus spp.
Calanus species at high latitudes accumulate large reserves of lipids (mainly wax esters) in oil sacs (Sargent
& Falk-Petersen 1988). Early copepodite stages have
relatively low levels of lipid, and most deposition of
wax esters occurs during stages IV and V (Sargent &
Falk-Petersen 1988). As a result of this accumulation
of lipid, large late-stage Calanus have a higher energy
content (J g–1) than earlier stages of Calanus (e.g. Comita
& al. 1966), other copepod species (e.g. Laurence 1976),
and other zooplankton groups (e.g. Williams & Robins
1979). In Placentia Bay, where capelin were relatively
small, few large Calanus were observed in capelin stomachs. Late-stage Calanus spp. are also rare in zooplankton samples collected in Placentia Bay during spring
and summer (Paul Snelgrove pers. commn). In other
areas (Trinity Bay, Avalon Peninsula, Northeast Grand
Banks, Funk Island Bank, Labrador) Calanus with visible oil droplets were common, particularly in the diet
of larger capelin. Capelin from these other areas were
larger-at-age in the spring than fish from Placentia Bay.
Skjoldal & al. (1992) reported an interaction between
zooplankton biomass (particularly Calanus finmarchicus Gunnerus), water temperature and capelin growth
in the Barents Sea. Low abundance of C. finmarchicus
in 1984 following an inflow of warm Atlantic water into
the Barents Sea contributed to low capelin growth rates
and a decline in capelin abundance. Recovery of zooplankton abundance in the late 1980s was accompanied
by an increase in capelin growth and biomass (Skjoldal
& al. 1992).
Similar large-scale fluctuations in growth and abundance of capelin have been observed in Newfoundland
waters in the 1990s. Since 1991 the mean length of mature age 3 and 4 capelin has decreased and the proportion of fish mature at age 2 has increased resulting in a
decrease in the size of spawning capelin compared to
the 1980s (Nakashima 1994; Carscadden & Nakashima
1997). This reduction in size in the early 1990s occurred
during a period of cooler water temperatures (Nakashima 1994), but the size of spawning adult capelin has
remained low in the late 1990s despite warming waters
(DFO 2000). The spatial distribution of capelin off Newfoundland also changed dramatically in the early 1990s
(review by Carscadden & Nakashima 1997). Acoustic
surveys, bottom-trawl surveys and cod-stomach-content analysis all showed a shift in the distribution of
capelin towards the south and east. Capelin virtually
disappeared from the northern part of their range off
Labrador (Carscadden & Nakashima 1997). At the same
time capelin increased in areas such as the Flemish Cap
and Scotian Shelf where they were not common previously (Frank & al. 1996). Capelin biomass in acoustic
surveys on the Northeast Newfoundland Shelf declined
dramatically in 1990-1991 and has remained low
(O’Driscoll & al. 2000).
We hypothesise that observed changes in capelin
growth in Newfoundland waters may be related in part
to spatial distribution and prey availability. Zooplankton
biomass in autumn is highest over the deep channels
and shelf break of the northern Newfoundland shelf
(Anderson & Dalley 1997; Dalley & al. 2000). Biomass
is lower to the south, especially on the plateau of Grand
Banks (Anderson & Dalley 1997; Dalley & al. 2000).
The composition of the zooplankton also varies between
areas (Pepin & Maillet 2000). Summer zooplankton
communities in northern areas tended to contain a higher
proportion of Calanus than communities further south,
that were dominated by smaller copepods (Pepin &
Maillet 2000). A southerly distribution of capelin, as
observed in the 1990s, may have resulted in poorer feeding conditions (especially a reduction in the availability of high lipid Calanus spp.) and reduced growth. Unfortunately no suitable time series of zooplankton abun-
O’Driscoll – Capelin feeding
dance are currently available to allow us to test this hypothesis.
Spatial distribution of capelin in Newfoundland waters appears to be returning to a more northern distribution (DFO 2000). In 1998 and 1999 capelin were observed in significant quantities in spring and autumn
acoustic surveys off southern Labrador for the first time
since 1990 (O’Driscoll & al. 2000). We are monitoring
the influence of these changes on capelin biology and
growth.
175
ACKNOWLEDGEMENTS
We thank all the sea-going scientific staff and crew of the
CCGS Teleost, especially John Anderson and Fran Mowbray.
Phil Eustace aged the capelin samples. Gary Maillet, John
Anderson, Pierre Pepin and three anonymous reviewers provided useful comments on this manuscript. Funding for this
work came from the NSERC Industrial Chair in Fisheries
Conservation and from a New Zealand Foundation for Research, Science and Technology Post-Doctoral Fellowship held
by the first author.
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Accepted 26 September 2000 – Printed 14 September 2001
Editorial responsibility: Tore Høisæter