EFFECTIVE STOCKING DENSITIES OF TRIPLOID GRASS
CARP TO CONTROL AQUATIC MACROPHYTES
by
MICHAEL WAYNE BRICE, B.S.
A THESIS
IN
WILDLIFE SCIENCE
Submitted to the Graduate Faculty
of Texas Tech University in
Partial Fulfillment of
the Requirements for
the Degree of
MASTER OF SCIENCE
Approved
May, 1995
•i
o
f\IO.'^^
ACKNOWLEDGMENTS
The author wishes to extend appreciation to Mr. Andrew
Sansom, Executive Director of Texas Parks and Wildlife
Department (TP&WD), for approving this research project and
for providing and stocking the triploid grass carp.
He would
also like to thank committee members Dr. Harold L. Schramm,
Dr. Nick C. Parker, and Dr. R. Scott Lutz.
Additional thanks
is extended to committee member Dr. Bill Harvey (TP&WD) for
bringing this research project to Texas Tech University.
This research project was funded by the Houston Livestock and
Rodeo Association and the National Biological Survey, Texas
Cooperative Fish and Wildlife Research Unit at Texas Tech
University.
This project could not have been accomplished
without the cooperation of private pond owners which included
Mr. Bill Gething, Mr. K. B. "Tex" Watson, Mr. Joe Weatherly,
and Cal Farley's Boys Ranch.
David A. Miko and Manuel T.
DeLeon assisted with the data collection.
The author also
extends special thanks to his family for their endless
support and to his wife and best friend for her love and
patience.
11
TABLE OF CONTENTS
ACKNOWLEDGMENTS
ii
ABSTRACT
iv
LIST OF TABLES
v
LIST OF FIGURES
vii
CHAPTER
I.
II.
III.
IV.
V.
INTRODUCTION
1
METHODOLOGY
6
Study Sites
6
Macrophyte Coverage
6
Triploid Grass Carp Stocking
8
Grazing Exclosures
9
Macrophyte Community Composition
10
Water Temperature and Water Transparency ...
10
Data Analyses
10
RESULTS
12
DISCUSSION
41
MANAGEMENT IMPLICATIONS
45
LITERATURE CITED
48
APPENDIX
54
111
ABSTRACT
Effective use of triploid grass carp
idella
Ctenopharyngodon
for control of aquatic macrophytes requires
determination of proper stocking densities.
The purpose of
this research was to evaluate three stocking densities of
triploid grass carp for control of aquatic macrophytes in
ponds of the Texas panhandle.
Triploid grass carp were
stocked in ponds with macrophyte coverage ranging from 0100%.
For each pond, percent macrophyte coverage was
estimated monthly along permanent transects with a recording
fathometer.
Macrophyte community composition, water
transparency, and water temperature were also monitored
monthly throughout this research.
From March 1991 to
September 1992, macrophyte coverage decreased 2.7% in ponds
stocked with 25 fish ha"^ (vegetated), 21.4% in ponds stocked
with 50 fish ha~l (vegetated) and 100% in ponds stocked with
75 fish ha~^ (vegetated).
Aquatic macrophytes were eliminated
in 12 months from ponds stocked with 75 fish ha"-"- (vegetated) .
Triploid grass carp stocked at 25 fish ha"^ did not allow
regrowth of vegetation in ponds that were previously treated
with herbicides.
Water transparency remained the same in
ponds stocked with 25 fish ha~l (vegetated), decreased 1.0% in
ponds stocked with 50 fish
ha~l (vegetated) , and decreased
58.1% in ponds stocked with 75 fish ha"^ (vegetated).
IV
LIST OF TABLES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Common and scientific names of aquatic macrophytes
identified in ponds in the Texas panhandle from
May 1991 to September 1992
13
Relative abundance (%) of aquatic macrophytes in
Gething South pond (L-1) from June 1991 to
April 1992
14
Relative abundance (%) of aquatic macrophytes in
Heritage II (L-2) from June 1991 to April 1992
15
Relative abundance (%) of aquatic macrophytes in
Swimming pond (L-3) from May 1991 to March 1992
16
Relative abundance (%) of aquatic macrophytes in
Fishing pond (M-5) from May 1991 to March 1992
17
Relative abundance (%) of aquatic macrophytes in
Gething Middle pond (M-6) from May 1991 to
April 1992
18
Relative abundance (%) of aquatic macrophytes in
Gething North pond (H-8) from May 1991 to
June 1992
19
Mean percent change in macrophytes coverage in
ponds stocked with 25 (Low), 50 (Medium), and 75
(High) triploid grass carp ha"-*- (vegetated)
22
Mean height of aquatic macrophytes measured (mm)
from June to September 1992 in grazed (G) and
non-grazed (NG) areas of ponds stocked with 2 5
(Low), 50 (Medium), and 75 (High) triploid grass
carp ha~l (vegetated)
29
Mean percent change in water transparency in ponds
stocked with 25 (Low), 50 (Medium), and 75 (High)
triploid grass carp ha"^ (vegetated)
31
Mean temperature of ponds stocked with 25 (Low),
50 (Medium), 75 (High) triploid grass carp ha~l
(vegetated)
39
V
12 .
13.
14.
15.
16.
Percent coverage of aquatic macrophytes from March
1991 to September 1992 in ponds stocked with 25
(Low=L), 50 (Medium=M), and 75 (High=H) triploid
grass carp ha~l (vegetated)
55
Water transparency measurements (cm) from March
1991 to September 1992 in ponds stocked with 25
(Low=L), 50 (Medium=M), and 75 (High=H) triploid
grass carp ha~l (vegetated)
56
Temperatures from May 1991 to September 1992 of
ponds stocked with 2 5 (Low=L), 50 (Medium=M), and
75 (High=H) triploid grass carp ha"^ (vegetated)
57
Water transparency measurements (cm) from March
1991 to September 1992 in ponds that were
initially void of vegetation when triploid grass
carp were stocked at 2 5 (Low=L), 50 (Medium=M),
and 75 (High=H) ha"!
58
Temperatures (^C) from May 1991 to September 1992
of ponds that were initially void of vegetation
when triploid grass carp were stocked at 2 5
(Low=L) , 50 (Medium=M) , and 75 (High=H) ha"!
VI
59
LIST OF FIGURES
1.
2.
3.
4.
5.
6.
7.
8.
9.
Percent change in macrophyte coverage from March
1991 to September 1992 in ponds stocked with 25
(Low), 50 (Medium), and 75 (High) triploid grass
carp ha-1 (vegetated)
20
Linear regression model of percent change in
macrophyte coverage as a function of month in
ponds stocked with 75 triploid grass carp ha"^
(vegetated)
23
A non-significant linear regression model of
percent change in macrophyte coverage as a
function of month in ponds stocked with 50
triploid grass carp ha~^ (vegetated)
24
A non-significant linear regression model of
percent change in macrophyte coverage as a
function of month in ponds stocked with 2 5
triploid grass carp ha"^ (vegetated)
25
Mean height of aquatic macrophytes from June
to September 1992 in grazed (G) and non-grazed
(NG) areas of ponds stocked with 2 5 (Low),
50 (Medium), and 75 (High) triploid grass
carp ha~^ (vegetated)
27
Percent change in water transparency from March
1991 to September 1992 in ponds stocked with 25
(Low), 50 (Medium), and 75 (High) triploid grass
carp ha~^ (vegetated)
30
Percent change in water transparency from May
1991 to September 1992 in Silver Springs Pond
(L-10), Heritage I Pond (M-11), and Horseshoe
Pond (H-12)
32
Linear regression model of percent change in
water transparency as a function of month in
ponds stocked with 7 5 triploid grass carp ha"^
(vegetated)
34
A non-significant linear regression model of
percent change in water transparency as a
function of month in ponds stocked with 50
triploid grass carp ha~l (vegetated)
35
Vll
10.
11.
12.
A non-significant linear regression model of
percent change in water transparency as a
function of month in ponds stocked with 25
triploid grass carp ha"^ (vegetated)
36
Water temperature at 0.1 m depth from May 1991 to
September 1992 in ponds stocked with 25 (Low), 50
(Medium), and 75 (High) triploid grass carp ha"^
(vegetated)
37
Water temperature at 0.1 m depth from May 1991 to
September 1992 in Silver Springs Pond (L-10),
Heritagel (M-11), and Horseshoe Pond (H-12)
38
Vlll
CHAPTER I
INTRODUCTION
Aquatic macrophytes (vascular plants and charophytes)
are a desirable component of aquatic systems.
Macrophytes
provide food, refuge, and reproductive habitat for a variety
of organisms.
In relatively shallow, clear-water systems
macrophytes often grow in large portions of the aquatic
habitat.
Such levels of vegetation can alter the dynamics of
fish communities and interfere with aquatic recreation.
Nuisance levels of macrophytes must be controlled to maintain
desirable predator-prey ratios and to allow maximum use of
aquatic resources.
Aquatic macrophytes can be controlled using mechanical,
chemical, and biological means.
Mechanical methods (physical
removal) are effective but costly and sometimes require
repeated treatments annually.
Additionally, mechanical
harvesters may cause high fish mortality (Haller et al.
1980).
Chemical control (herbicides) is also effective, but
application of approved chemicals is expensive (Stott et al.
1971; Shireman 1982), and multiple treatments sometimes are
needed for year-around control.
Chemicals may also have
detrimental effects on fish food organisms and can lead to
contamination of sediments (Engel 1990).
An alternative to
mechanical and chemical methods is biological control of
1
2
nuisance aquatic vegetation.
Biological control of
undesirable vegetation can be achieved through the selective
use of other organisms, such as herbivores or pathogens.
Biological methods have been advocated as having great
potential for effective, economic and long-term control of
aquatic vegetation (Mulligan 1969; Bailey 1972).
An effective biological control agent for many aquatic
macrophytes is the grass carp Ctenopharyngodon
idella
(Swingle 1957; Hickling 1965; Cross 1969; Michewicz et al.
1972; Sutton 1977; Swanson and Bergersen 1988; Sample 1990).
This herbivorous fish is indigenous to large rivers in the
eastern part of Russia and China that flow to the Pacific
Ocean between latitudes 50° North and 23° North (Berg 1949) .
The grass carp has been introduced into more than 50
countries, including the U.S., for control of aquatic
vegetation and as a species of importance to aquaculturists
(Shireman and Smith 1983).
The widespread use of grass carp for vegetation control
in the U.S. has been limited by the threat of these fish
escaping into aquatic systems where population expansion and
subsequent reduction of desirable vegetation could take place
(Allen and Wattendorf 1987).
Triploid induction is an
effective method to eliminate reproductive capabilities of
grass carp (Wiley et al. 1987).
Grass carp are normally
diploid with a chromosome number (2N) of 48; however,
3
individuals with three sets of chromosomes, triploids (3N),
have been produced in hatcheries (Malone 1984) . Triploid
grass carp (TGC) are produced in the same way as diploid
grass carp (DGC), except that fertilized eggs subjected to
heat, cold, or pressure shock retain an extra set of
chromosomes (72 total) and result in sterile offspring.
Gonads develop in TGC, but their gametes are not viable
(Purdon 1983; Thorgaard 1983).
Triploid grass carp's
behavior and vegetation consumption are essentially the same
as DGC (Wattendorf and Anderson 1984; Wiley and Wike 1986) .
Food habits of grass carp change as the fish grow and
develop.
As fry, grass carp primarily feed on small animals.
Opuszynski (1968) reported that fish of 11-15 mm total length
(TL) feed mainly on rotifers and crustaceans, and fish of 1718 mm TL feed more heavily on chironomids.
carp feed exclusively on microflora.
At 30 mm TL grass
Watkins et al. (1981)
found that fish of 17-31 mm TL consumed benthic
invertebrates, whereas fish 32-86 mm consumed principally
periphyton.
As grass carp grow, they consume increased
proportions of aquatic macrophytes (Opuszynski 1972) and at
200-550 mm TL, aquatic macrophytes become a regular part of
their diet (Lin 1935; Krondradt 1966; Opuszynski 1968;
Ciborowska 1972; Shireman and Smith 1983).
Grass carp consume a wide variety of plant species
(Avault 1965b; Pentelow and Stott 1965; Stott and Robson
4
1970; Michewicz et al. 1972; Fowler and Robson 1978; Swanson
and Bergersen 1988; Sample 1990; Bettoli 1991).
Initially
preferred vegetation types include filamentous algae and
young, tender species of Callitriche,
Fontinalis,
Lemma, Najas,
Spirodella
Nitella,
Chara,
Paspalum,
Elodea,
Potomogeton,
and
(Lin 1935; Opuszynski 1972, 1979; Edwards 1974,
1975; Sutton 1977).
As grass carp grow larger, they become
less selective and consume a wider variety of emergent and
submergent aquatic macrophytes (Bailey 1972; Edwards 1974,
1975) .
Some of the plant species preferred by adult grass
carp include Ceratophyllum
demersum,
verticillata,
spp., Najas
spp.
Myriophyllum
Chara spp.,
spp., and
Hydrilla
Potomogeton
Fibrous or woody reeds, sedges, and rushes have low
selectivity (Prowse 1971).
The daily consumption of vegetation by grass carp varies
with water temperature and size of the fish.
Triploid grass
o
carp feeding begins at 3-6 C but is irregular, becomes steady
o
o
at about 14 C, peaks at 2 0-2 6 C, and may decrease at about
33°C (Clugston and Shireman 1987).
Opuszynski (1972) found
that the daily consumption of grass carp was about 50% of
body weight at 20°C and 100-120% of body weight at 22-33°C.
Wattendorf and Anderson (1984) found similar consumption
rates for TGC.
Cure (1970) and Edwards (1974) both reported
that grass carp consume up to their body weight in vegetation
per day at 20-23°C and 20-28°C, respectively.
Effective use of TGC for vegetation control requires
determination of proper stocking densities.
Various
combinations of numbers per unit area and sizes have been
used in different environments (Avault 1965a, 1965b; Sills
1970; Mitzner 1974; Van Dyke et al. 1984; Noble et al. 1986).
Most stocking densities have been based on surface area of
water and not area of vegetation.
Swanson and Bergersen
(1988) suggested that water temperature, density,
distribution, and species of aquatic plants, human
disturbance, management objectives, and size of fish should
all be considered when determining stocking densities of
grass carp for aquatic vegetation control.
Blackburn (197 5)
also suggested that the size of the fish stocked as well as
the species and abundance of vegetation present should be
considered when establishing stocking densities.
The purpose
of this research was to evaluate three stocking densities of
TGC for control of aquatic macrophytes in ponds of the Texas
panhandle.
CHAPTER II
METHODOLOGY
Study Sites
Twelve privately owned ponds located in Donley, Gray,
Oldham, and Wheeler counties, Texas, were the sites for this
research.
Surface area of the ponds ranged from 0.16 to 2.83
hectares.
Maximum depth of the ponds ranged from 2.0 to 4.0
meters.
All ponds contained dense growths of
Ceratophyllum,
Myriophyllum,
or Najas,
Chara,
in 3 0% or more of the
pond surface based on visual estimates in 1989 or 1990.
Prior to 1991, several of these ponds had received chemical
treatments for control of aquatic vegetation; however, no
ponds received chemical treatments during this research.
All ponds were managed for recreational fishing.
fish communities included channel catfish
punctatus,
macrochirus,
green sunfish Lepomis
cyanellus,
redear sunfish L. microlophus,
bass Micropterus
The
Ictalurus
bluegill L.
and largemouth
salmoides.
Macrophyte Coverage
The perimeter of each pond was mapped using standard
surveying procedures.
Permanent transects were then selected
to survey depth and vegetation conditions in each pond.
The
ends of each transect were marked on shore and these points
were surveyed and marked on the map.
Transects were
conducted with a 4.3-m aluminum, flat-bottom boat powered by
an electric trolling motor.
Along these transects, pond
bathymetry and macrophyte abundance were measured with a
recording fathometer (Maceina and Shireman 1980).
A Lowrance
X-16 recording fathometer depth sounder (Lowrance
Electronics, Inc., Tulsa, Oklahoma) equipped with a 20 cone
angle transducer was utilized for all vegetation transects.
Total percent coverage of aquatic macrophytes was
estimated along permanent transects using fathometer tracings
(Maceina and Shireman 1980).
This was accomplished by
observing every 0.3 m of each transect tracing and recording
either a presence (hit) or absence (miss) of vegetation.
If
a transect could not be completed due to impassable shallow
water, dense macrophyte growth, or any other obstruction
along the transect, the remaining length of the transect, as
well as the percent coverage of macrophytes along that
remaining length of transect, were approximated visually.
Visual estimates of percent macrophyte coverage were
converted to hits per transect length by multiplying the
estimated macrophyte coverage by the estimated remaining
transect length/0.3.
Total percent coverage of macrophytes
for each pond was calculated by dividing the total number of
hits of all transects by the total number of hits and misses
of all transects.
Vegetation density along transects was
8
measured monthly in May through November 1991, and in
January, and March through September 1992.
Triploid Grass Carp Stocking
In aquatic systems where predators are present, grass
carp should be stocked at sizes that make them less
susceptible to predation.
Shireman et al. (1978) calculated
that stocking grass carp > 450 mm TL was necessary to totally
eliminate the possibility of predation by Florida largemouth
bass Micropterus
salmoides
floridanus.
To prevent loss of
grass carp to largemouth bass predation, TGC with a mean
weight of 0.97 kg and a mean length of 440 mm TL were stocked
into the research ponds.
Fish were stocked in March 1991 at
densities of 25, 50, and 75 fish ha -1 (vegetated) . All fish
were certified as triploids and stocked by Texas Parks and
WiIdlife Department.
At the time of stocking, nine ponds contained 50% or
more areal coverage of macrophytes and three ponds were void
of macrophytes.
The ponds void of macrophytes had been
treated with herbicides in the summer of 1990 to control
vegetation which had covered 100% of the ponds surface area
at the time of treatment.
Stocking densities for these ponds
were based on surface area of vegetation prior to herbicide
application.
Throughout this thesis, ponds will be
referenced with a letter which corresponds with the stocking
9
density assigned to it; L = low density ponds (25 fish ha"^) ,
M = medium density ponds (50 fish ha"^) , and H = high density
ponds (75 fish ha"^) .
Ponds are also numbered 1-12.
Grazing Exclosures
In March 1992, one or two grazing exclosures were
randomly placed within the littoral zone of each of the
twelve research ponds to monitor vegetation in grazed and
non-grazed areas of each system.
Exclosures 1-m long x 1-m
wide X 2-m high were constructed of 1.8-m metal t-posts and
galvanized poultry fencing 5.0-cm x 3.8-cm mesh.
Exclosures
were equipped with tops to avoid grass carp entry.
The height of aquatic macrophytes inside and outside
each exclosure was measured monthly, from June 1992 to
September 1992.
On each occasion, four plants of each
species identified inside the exclosures were randomly
selected and measured (mm). For each species measured inside
the exclosure, four plants of the same species were measured
(mm) within 1 m outside of the exclosure.
All plants that
were measured were growing at approximately the same depth.
All plants were measured from the hydrosoil to their longest
vegetative structure.
At the time the exclosures were placed
into the ponds, 13 of 22 of the exclosures were void of
macrophytes.
10
Macrophyte Community Composition
Plant community composition was determined each time
vegetation coverage was measured.
As vegetation transects
were conducted, floating marker buoys were randomly dropped
along the transects such that 15 buoys were located at each
water depth of 0-1 m, 1-2 m, and > 2 m.
At each buoy, I
obtained a macrophyte sample with a grappling device.
For
each sample, all species were identified and assigned a
percent relative abundance by volume.
Plant community
composition was calculated as mean percent relative abundance
of all samples taken from a pond on a sampling date.
Water Temperature and Water Transparency
Water temperature and water transparency were recorded
on each occasion that transects were conducted.
Water
temperature was measured at approximately the center of each
pond at 0.1 m depth.
Water transparency, measured at the
deepest location of each pond, was the average of the depth
(cm) at which a Secchi disc disappeared as it was lowered
into the water column and the depth (cm) at which it
reappeared as it was being raised back to the water surface.
Data Analyses
The effect of the three stocking densities on aquatic
macrophyte coverage, plant height, water transparency, and
11
water temperature were each tested by repeated measures
analysis of variance.
These analyses included only the nine
ponds that contained vegetation at the beginning of the
study.
For these analyses, the dependent variables were
percent change in macrophyte coverage, plant height, percent
change in water transparency, and temperature.
The
independent variables for these analyses were month and
stocking density.
Fisher's protected least significance
difference test (FLSD) was used to separate the means
following a significant F test.
Simple linear regression analyses were used to construct
models for each stocking density which explain the percent
change in macrophyte coverage and water transparency over
time.
For each model. Ho: Bi=0 was tested using analysis of
variance.
All statistical tests were conducted at a significance
level of P < 0.05.
CHAPTER III
RESULTS
Eight species of aquatic macrophytes were identified in
nine of the twelve research ponds from May 1991 to April 1992
(Table 1 ) . During this period, six ponds maintained mixedplant communities consisting of two to six species and three
ponds maintained monotypic stands of vegetation.
All low
stocking density ponds were comprised of mixed-plant
communities.
In March 1991, dominant or codominant plant
species were C. demersum,
2-4).
Chara,
and N. guadalupensis
(Tables
Medium stocking density ponds were comprised of two
mixed-plant communities and one monotypic stand.
1991, dominant or codominant plant species were C.
and Chara
(Tables 5-6) .
Myriophyllum
species of the monotypic stand.
spicatum
In March
demersum
was the
High stocking density ponds
were comprised of one mixed-plant community and two monotypic
stands.
In March 1991, codominant plant species of the
mixed-plant community were Chara and N. guadalupensis
7) . Myriophyllum
spicatum
(Table
was the species of the two
monotypic stands.
From March 1991 to September 1992, macrophyte coverage
decreased 2.7% in low stocking density ponds, 21.4% in medium
stocking density ponds, and 100% in high stocking density
ponds (Figure 1). From March 1991 to September 1992, the
12
13
Table 1.
Common and scientific names of aquatic macrophytes
identified in ponds in the Texas panhandle from May
1991 to September 1992.
Common Name
Scientific Name
Coontail
Ceratophyllum
Stonewort
Chara
Eurasian watermilfoil
Myriophyllum
Southern naiad
Najas
Curlyleaf pondweed
Potamogeton
Illinois pondweed
Potamogeton
American pondweed
Potamogeton
Sago pondweed
Potamogeton
demersum
spp
spicatum
guadalupensis
crispus
illinoiensis
nodosus
pectinatus
14
Table 2.
Relative abundance (%) of aquatic macrophytes in
Gething South pond (L-1) from June 1991 to April
1992.
a
.
Species
Date
Cede
Chara
Nagu
Poll
Pono
Pope
06/91
3.33
70.03
0.00
7.47
0.00
19.17
07/91
8.33
58.97
22.20
1.33
0.00
9.17
08/91
6.57
25.20
47.33
7.43
4.43
9.03
09/91
7.67
24.13
49.07
8.00
4.44
6.69
10/91
8.89
13.56
59.78
10.00
4.56
3.22
01/92
6.78
11.67
53.53
15.80
1.11
11.11
03/92
2.22
54.42
28.56
13.33
0.00
1.47
04/92
8.00
27.24
40.76
14.78
0.00
9.22
Mean
6.47
35.65
37.65
9.76
1.81
8.63
^Cede = Ceratophyllum
demersum,
Nagu = Najas guadalupensis,
Pono = Potamogeton nodosus.
Chara = Chara spp.,
Poll = Potamogeton
Pope = Potamogeton
illinoiensis,
pectinatus.
15
Table 3.
Relative abundance (%) of aquatic macrophytes in
Heritage II (L-2) from June 1991 to April 1992.
a
Soecies
Date
Cede
Chara
Pono
Pope
06/91
70.45
19.05
10.00
0.50
07/91
69.17
11.33
17.17
2.33
08/91
93.13
0.00
5.33
1.53
09/91
91.83
0.00
8.00
0.17
10/91
92.33
0.00
7.50
0.17
04/92
91.00
1.17
6.33
1.50
Mean
84.65
5.25
9.05
4.95
^Cede = Ceratophyllum
Pono = Potamogeton
demersum,
nodosus.
Chara = Chara
Pope = Potamogeton
spp.,
pectinatus.
16
Table 4
Relative abundance (%) of aquatic macrophytes in
Swimming pond (L-3) from May 1991 to March 1992.
Species
Date
Chara
Pope
05/91
78.20
21.80
06/91
100.00
0.00
07/91
90.50
9.50
08/91
86.67
13.33
09/91
100.00
0.00
10/91
100.00
0.00
01/92
67.33
32.67
03/92
78.30
21.70
Mean
87.62
12.37
^Chara = Chara spp.. Pope = Potamogeton
pectinatus
17
Table 5.
Relative abundance (%) of aquatic macrophytes in
Fishing pond (M-5) from May 1991 to March 1992.
Species
Date
Chara
Nagu
Pope
05/91
100.00
0.00
0.00
06/91
100.00
0.00
0.00
07/91
92.14
0.00
7.86
08/91
62.74
10.93
26.33
09/91
55.33
0.00
44.67
10/91
62.13
25.20
12.67
01/92
80.67
12.17
7.17
03/92
88.50
5.17
6.33
Mean
80.18
6.68
13.12
^Chara = Chara spp., Nagu = Najas guadalupensis.
Pope = Potamogeton pectinatus
18
Table 6. Relative abundance (%) of aquatic macrophytes in
Gething Middle pond (M-6) from May 1991 to April
1992.
a
Species
Date
Cede
Chara
Nagu
Poor
Pope
05/91
335.50
5 ..50
448.83
8 ,.83
15.67
0.00
0.00
06/91
660.00
0 .,00
440.00
0 ,.00
0.00
0.00
0.00
07/91
551.50
1 ..50
447.75
7 ,. 7 5
0.75
0.00
0.00
08/91
6 9 .. 9 3
69.93
113.17
3 ,.17
16.90
0.00
0.00
09/91
889.00
9 ,.00
33.33
,. 3 3
6.00
0.00
1.67
10/91
770.47
0 ,.47
0,
.67
0.67
6.83
0.00
22.03
01/92
5 4 ,. 5 0
54.50
1 0 ,. 0 0
10.00
1.00
7.00
27.50
03/92
444.53
4 ,.53
2 2 ,.80
22.80
0.00
21.50
11.17
04/92
339.70
9 ,. 7 0
330.97
0 ,.97
0.00
12.83
16.50
Mean
57.23
24.17
5.23
4.58
8.76
^Cede = Ceratophyllum demersum, Chara = Chara spp.,
Nagu = Najas guadalupensis,
Poor = Potamogeton crispus.
Pope = Potamogeton
pectinatus
19
Table 7.
Relative abundance (%) of aquatic macrophytes in
Gething North pond (H-8) from May 1991 to June
1992.
a
Species
Date
Chara
Nagu
05/91
62.50
37.50
0.00
06/91
35.00
55.00
10.00
Mean
48.75
46.25
5.00
^Chara = Chara spp., Nagu = Najas
Pope = Potamogeton
pectinatus.
guadalupensis.
Pope
20
Low
•^—
High
Medium
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TIME
Figure 1.
Percent change in macrophyte coverage
from March 1991 to September 1992 in
ponds stocked with 25 (Low), 50
(Medium), and 75 (High) triploid
grass carp ha
-1
(vegetated).
21
mean percent change in macrophyte coverage in high stocking
density ponds (Mean = -66.6, SE = 6.0, N = 43) was different
(P<0.05) from the mean percent change in macrophyte coverage
in medium stocking density ponds (Mean = -11.1, SE = 2.8,
N = 39) and low stocking density ponds (Mean = -2.8, SE =
0.9, N = 45, Table 8). The three ponds that were void of
macrophytes in March 1991 remained void throughout the study.
Simple linear regression analysis indicated a
significant relationship between month and percent change in
macrophyte coverage for high stocking density ponds (R =
0.58, P < 0.0001, Figure 2).
The regression yielded the
model:
% CHG. M.C.= -10.451 + -5.575 (M);
where % CHG. M.C. is percent change in macrophyte coverage
and M is the number of months following the stocking of TGC.
A non-significant relationship between month and percent
change in macrophyte coverage was indicated for medium
stocking density ponds (R =0.01, P = 0.50, Figure 3) and low
stocking density ponds (R^ = 0.01, P = 0.54, Figure 4 ) .
Species composition of almost all mixed-plant
communities changed as the study progressed.
In Gething
22
Table 8.
Mean percent change in macrophyte coverage in ponds
stocked with 25 (Low), 50 (Medium), and 75 (High)
triploid grass carp ha"! (vegetated) . Means
followed by different letters are significantly
different (P<0.05).
Stocking density
N
Mean
SE
High
43
-66.6^
6.0
Medium
39
-11.1^
2.8
Low
45
-2.8^
0.9
23
% CHG. M . C .
= -10.451 +
(R^ = 0 . 5 8 ,
P <
-5.575
0.0001)
H
O
>
O
U
H
E-i
>H
CU
O
Pi
U
pa
o
u
EH
pa
u
(^
pa
12
14
16
MONTH
Figure 2.
Linear regression model of percent
change in macrophyte coverage as a
function of month in ponds stocked
-1
with 75 triploid grass carp ha
(vegetated). In the regression
model, % CHG. M.C. is percent change
in macrophyte coverage and M is the
number of months following the
stocking of the fish.
18
24
% CHG. M.C. = -7.368 + -0.332 (M)
(R^ = 0.01, P = 0.50)
pa
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30-j
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20-1
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10-i
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•
•
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•
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•
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•
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-60-j
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inn "
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0
'
1
1 '
1 ' 1
6
8
'
1
10
1
12
•
1
14
'
1
16
MONTH
Figure 3.
A non-significant linear regression
model of percent change in macrophyte
coverage as a function of month in
ponds stocked with 50 triploid grass
-1
carp ha (vegetated). In the
regression model, % CHG. M.C. is
percent change in macrophyte coverage
and M is the number of months
following the stocking of the fish.
'
18
25
% CHG. M.C. = -1.682 + -0.101 (M)
(R^ = 0.01, P = 0.54)
40
O
30i
pa
20-j
>
o
u
10-i
pa
o4^
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o
p^
u
•
•
•
•
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•
•
•
•
•
•
•
<
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-20-j
-30-^
H
-40-j
pa
o
-50-j
u
-604
EH
-70-j
pa
o
p^
-80-=
pa
-90-j
100-
—
0
-|
6
1 — I
1 — I — I — I — I — I — I — I
8
10
12
14
1 -
16
MONTH
Figure 4
A non-significant linear regression
model of percent change in macrophyte
coverage as a function of month in
ponds stocked with 25 triploid grass
-1
carp ha
(vegetated). In the
reggression model, % CHG. M.C. is
percent change in macrophyte coverage
and M is the number of months
following the stocking of the fish.
18
26
South Pond (L-1) , Chara decreased from 70% to 27% while N.
guadalupensis
increased from 0% to 40% (Table 2 ) .
In
Heritage II Pond (L-2), Chara decreased from 19% to 1% and C.
demersum
increased from 70% to 91% (Table 3).
In Fishing
Pond (M-5), Chara decreased from 100% to 80% while P.
pectinatus
and N.
guadalupensis
increased from 0% to 6% and
0% to 5%, respectively (Table 5). Gething Middle Pond (M-6)
showed a decrease in N. guadalupensis
(15% to 0%) and Chara
(48% to 30%) and an increase in P. pectinatus
demersujn (35% to 39%) , and P. crispus
(0% to 16%), C.
(0% to 12%, Table 6) .
In Gething North Pond (H-8), Chara decreased from 62% to 3 5%
while N.
guadalupensis
and P. pectinatus
increased from 37%
to 55% and 0% to 10%, respectively (Table 7 ) .
By June 1992, macrophytes were present in all the
exclosures located in ponds that had macrophytes present in
March 1991.
Macrophytes remained in these exclosures for the
duration of the study.
Macrophytes of similar height were
present in grazed and non-grazed areas of low and medium
stocking density ponds from June to September 1992 (Figure
5) . During this same time, macrophytes were also present in
non-grazed areas of high stocking density ponds; however, all
macrophytes were eliminated from grazed areas of high
stocking density ponds by July 1992 (Figure 5).
From June to
September 1992, plant height was different (P < 0.05)
27
15
CI
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28
between grazed areas of high stocking density ponds (Mean =
33.0, SE= 29.0, N = 22) and non-grazed areas high stocking
density ponds (Mean = 694.4, SE = 52.0, N = 22,
Table 9 ) .
No differences in plant height were detected between grazed
and non-grazed areas of either medium stocking density ponds
(P = 0.481) or low stocking density ponds (P = 0.752).
Macrophytes were never found in the exclosures located in
ponds that were void of macrophytes in March 1991.
From March 1991 to September 1992, water transparency
remained the same in low stocking density ponds, decreased
1.0% in medium density ponds, and decreased 58.1% in high
stocking density ponds (Figure 6).
From March 1991 to
September 1992, the mean percent change in water transparency
in high stocking density ponds (Mean = -22.1, SE = 4.3, N =
48) was different (P < 0.05) from the mean percent change in
water transparency in medium stocking density ponds (Mean =
1.7, SE = 1.4, N = 48) and low stocking density ponds (Mean =
0.8, SE = 0.2, N = 48, Table 10). From March 1991 to
September 1992, water transparency decreased in all three
ponds that were void of macrophytes in March 1991.
Water
transparency decreased 57.1% in Silver Springs Pond (L-10),
48.0% in Heritage I Pond (M-11), and 50.0% in Horseshoe Pond
(H-12), Figure 7 ) .
Simple linear regression analysis indicated a
significant relationship between month and percent change in
29
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30
Low
•^— Medium
High
>H
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pc;
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pa
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TIME
Figure
6
oq
Percent change in water transparency
from March 1991 to September 1992 in
ponds stocked with 25 (Low), 50
(Medium), and 75 (high) triploid
-1
grass carp ha
(vegetated).
31
Table 10. Mean percent change in water transparency in ponds
stocked with 25 (Low), 50 (Medium), and 75 (High)
triploid grass carp ha"! (vegetated) . Means
followed by different letters are significantly
different (P<0.05).
Stocking density
N
Mean
SE
High
48
-22.1^
4.3
Medium
48
1.7^
1.4
Low
48
0.8^
0.2
32
L-10
^^—
M-11
H-12
>H
U
H
pc:
<:
Ot
CO
p:J
pa
EH
I
H
pa
o
u
EH
pa
u
Pi
pa
PM
0^
S
CJ^
is; ^^
<r>
(Tl
CTi
(Tl
tJ)
ft
fj
Id
Q)
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<;
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a
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^^
1^
(Ti
S
:i
:3
CN
CN
cn
cn
m
Q
H)
^
<:
TIME
Figure
7.
Percent change in water transparency
from March 1991 to September 1992 in
Silver Springs Pond (L-10), Heritage
I Pond (M-11), and Horseshoe Pond
(H-12). These ponds were void of
vegetation when triploid grass carp
were stocked at 25 (L), 50 (M), and
-1
75 (H) ha .
W
33
water transparency for high stocking density ponds (R^ = 0.41,
P < 0.0001, Figure 8.). The regression yielded the model:
% CHG. W.T.= 12.059 + -3.474 (M) ;
where % CHG. W.T. is percent change in water transparency and
M is the number of months following the stocking of TGC.
A
non-significant relationship between month and percent change
in water transparency was indicated for medium stocking
density ponds (R^ = 0.001, P = 0.81, Figure 9) and low
stocking density ponds (R^ = 0.001, P = 0.84, Figure 10).
From May 1991 to September 1992, water temperature of
all ponds followed similar seasonal fluctuations (Figures 11
& 12). Temperatures of ponds that had vegetation present in
March 1991 ranged from 6.6 to 27.8°C in low stocking density
ponds, 6.5 to 27.8°C in medium stocking density ponds, and
6.8 to 28.5°C in high stocking density ponds (Figure 11).
From March 1991 to September 1992, the mean temperature of
high stocking density ponds (Mean = 19.1, SE = 1.1, N = 36),
medium stocking density ponds (Mean = 19.2, SE = 1.0, N =
37), and low stocking density ponds (Mean = 18.3, SE =
.1,
N = 37) were not different (Table 11). Temperatures of ponds
that were void of vegetation in March 1991 ranged from 6.1 to
27.0°C in Silver Springs Pond (L-10), 5.0 to 27.5°C in
Heritage I Pond (M-11), and 6.1 to 27.5°C in Horseshoe Pond
34
% CHG. W.T. = 12.059 + -3.474 (M)
(R^ = 0.41, P < 0.0001)
70T
>H
U
pa
CO
pcj
ca
I
H
pa
o
u
EH
s
pa
u
p^
pa
Pl4
12
14
16
MONTH
Figure 8
Linear regression model of percent
change in water transparency as a
function of month in ponds stocked
, -1
with 75 triploid grass carp ha
(vegetated). In the regression model,
% CHG. W.T. is percent change in water
transparency and M is the number of
months following the stocking of the
fish.
18
35
% CHG. W . T .
= 1.116
(R^ = 0 . 0 0 1 ,
+ 0.056
P =
(M)
0.81)
u
pa
<
CO
Pi
pa
EH
H
pa
o
u
EH
pa
u
Pi
pa
PU
MONTH
Figure 9.
A non-significant linear regression
model of percent change in water
transparency as a function of month in
ponds stocked with 50 triploid grass
carp ha""*" (vegetated) . In the
regression model, % CHG. W.T. is
percent change in water transparency
and M is the number of months
following the stocking of the fish.
36
% CHG. W.T. = 0 . 6 3 0 + 0 . 0 0 8
(R^ = 0 . 0 0 1 ,
(M)
P = 0.84)
U
pa
CO
Pi
pa
EH
O
U
EH
pa
a
pcj
pa
PU
MONTH
Figure 10
A non-significant linear regression
model of percent change in water
transparency as a function of month in
ponds stocked with 2 5 triploid grass
carp ha~ (vegetated). In the
regression model, % CHG. W.T. is
percent change in water transparency
and M is the number of months
following the stocking of the fish.
37
r>
Low
High
Medium
u
o
pa
pci
o
EH
pa
PU
s
pa
EH
p^
pa
EH
>1
(0
s
0)
7i
<
ft
V
<U
W
u
o
>
0
c
trt
s
1^
^
Q)
\^
u
u
s
^
rtl
ft
>1
(0
^
c
3
1^
iH
3
^^
CD
^
<:
TIME
Figure 11. Water temperature at 0.1 m depth
from May 1991 to September 1992 in
ponds stocked with 25 (Low), 50
(Medium), and 75 (High) triploid
-1
grass carp ha
(vegetated).
ft
Q)
CO
38
L-10
•^>— M - 1 1
H-12
U
o
pa
pc;
o
EH
pa
PU
pa
EH
»;
pa
EH
TIME
Figure 12. Water temperature at 0.1 m depth
from May 1991 to September 1992 in
Silver Springs Pond (L-10), Heritage
I Pond (M-11), and Horseshoe Pond
(H-12).
These ponds were void of
vegetation when triploid grass carp
were stocked at 25 (L), 50 (M), and
, -1
75 (H) ha .
39
Table 11.
Mean temperature of ponds stocked with 25 (Low),
50 (Medium), and 75 (High) triploid grass carp
ha"l (vegetated). Means followed by the same
letters are not significantly different (P>0.05).
Stocking density
N
Mean
SE
High
36
19.1^
1.1
Medium
37
19.2^
1.0
Low
37
18.3^
1.1
40
(H-12) (Figure 12). For all of the ponds in the study, the
lowest temperatures occurred in January 1992 and the highest
temperatures occurred in August 1991 (Figures 11 & 12) .
CHAPTER IV
DISCUSSION
Triploid grass carp were effective in controlling
aquatic macrophytes in small ponds of the Texas panhandle.
Aquatic macrophytes were eliminated from ponds stocked with
75 triploid grass carp (mean weight =0.97 kg, mean
length = 440 mm TL) ha"^ (vegetated) in 12 months.
These
results are similar to those found by Klussmann et al.
(1988), where DGC (200-300 mm TL) stocked at 74 fish ha"^
(vegetated) eliminated all acjuatic macrophytes from Lake
Conroe (8100 ha), Texas in 2 years.
•
-
In Colorado, similar
1
stocking densities (64-74 fish ha
) controlled acjuatic
macrophytes in 3-4 years (Swanson and Bergerson 1988).
Higher stocking densities than those I used for ponds of
the Texas panhandle have resulted in the control of aquatic
macrophytes in less time.
In Florida, hydrilla was
controlled 6 months after stocking 95 DGC (mean weight =
1.08 kg) ha"-^ (Sutton et al. 1978).
In Texas, 54 DGC (mean
length = 270 mm TL, mean weight = 0.242 kg) and 54 hybrid
(male bighead carp Hypophthalmichthys
nobilis
X female grass
carp) grass carp (mean length = 234 mm TL, mean weight = 0.14
kg) ha""*" (vegetated) eliminated vegetation from Lewis Creek
Reservoir (420 ha) in 8 months (Noble et al. 1986).
41
42
A model simulating vegetation control of a shallow pond
in Houston, Texas, predicted that 79-13 0 TGC (0.15 kg) ha""^
(vegetated) would need to be stocked to remove 60% of the
macrophyte biomass in 2 years (Santha 1990).
The stocking
density range recommended by the model exceeded the 75 fish
ha
(vegetated) we used for ponds of the Texas panhandle;
however, the rate at which macrophytes were removed from
ponds of the Texas panhandle exceeded the predicted
macrophyte reduction rate of the simulated pond in Houston,
Texas.
These contrasting results can probably be attributed
to the size of the fish stocked and geographical location.
If larger fish were used in the model simulation, the
macrophyte reduction rate would probably be more similar to
that which occurred in ponds of the Texas panhandle.
The
contrasting results also seem to indicate that higher
stocking densities of TGC may be needed to control vegetation
in ponds of warmer climates.
From March 1991 to September 1992, macrophyte coverage
in ponds of the Texas panhandle decreased 2.7% in ponds
stocked with 25 fish ha""^ (vegetated) and decreased 21.4% in
ponds stocked with 50 fish ha""^ (vegetated) . These results
were similar to those found by Kirk (1992) where 50 or less
TGC (200-280 mm TL) ha""^ (vegetated) failed to control aquatic
macrophytes in South Carolina farm ponds (0.1 to 5.7 ha) in 3
years.
43
In the mixed-plant community ponds of the Texas
panhandle, TGC seemed to prefer Chara,
and thus reduced its
coverage, while other species such as P. pectinatus,
demersum,
and N. guadalupensis
C.
increased in coverage.
Fowler
and Robson (1978) reported similar results where grass carp
preferred Chara to seven other macrophytes.
However,
Opuszynski (1972) and Pine and Anderson (1991) found Chara
one of the least preferred species consumed by grass carp.
A common response to the removal of acjuatic macrophytes
is a decrease in water transparency (Mitzner et al. 1978;
Canfield et al. 1983; Noble et el. 1986; Klussmann et al.
1988; Woltmann 1988).
I found that water transparency of
ponds of the Texas panhandle decreased 56% when acjuatic
macrophytes were eliminated.
Decreases in water transparency
are likely associated with changing planktonic biomass
(Klussmann et al. 1988).
Nutrients that are bound by
macrophytes are released into the water column after the
macrophytes are consumed by grass carp.
As a result, these
nutrients become available to phytoplankton, and thus an
increase in phytoplankton biomass occurs.
Klussmann et al.
(1988) noted that elimination of acjuatic macrophytes from
Lake Conroe, Texas, resulted in a production shift from a
macrophyte-based system to a phytoplankton-based system.
Wind erosion and subsequent deposition of soil particles into
44
the water column can also cause declines in water
transparency.
Changes in water transparency may ultimately affect the
amount of acjuatic macrophytes produced in a system.
As water
transparency decreases, the photic zone becomes shallower,
and thus decreasing the area of littoral habitat where
aquatic macrophytes can grow.
A decrease in the water
transparency may have been the reason acjuatic macrophytes
never reappeared in the grazing exclosures of ponds that were
initially void of macrophytes when TGC were stocked.
After macrophytes are eliminated, fewer TGC should be
required to control the regrowth of macrophytes.
Sutton et
al. (197 8) kept hydrilla from reappearing in a pond (0.31 ha)
in Florida by stocking 16 grass carp ha -1 . I found that
m
ponds that had been previously treated with herbicides, 10
TGC ha~
did not allow regrowth to occur.
using fewer than 10 fish ha~
Additional research
is needed to determine the
minimal stocking density required to control the regrowth of
aquatic macrophytes.
CHAPTER V
MANAGEMENT IMPLICATIONS
The use of TGC for the control of nuisance aquatic
macrophytes is an effective and cost efficient management
strategy that offers long-lasting results.
Utilization of
these fish as a management tool recjuires knowledge of their
effectiveness in controlling various species of vegetation at
different sizes and densities.
The desired level of acjuatic
macrophyte control should be determined by the overall
management objective of each individual system.
Results of
this research give a good indication of the efficacy of TGC
in controlling aquatic macrophytes in small ponds of the
Texas panhandle.
Total eradication of aquatic macrophytes may be the
desired objective.
Examples in which the complete removal of
aquatic vegetation is desired are maintenance of irrigation
canals and aquaculture ponds.
Complete removal of acjuatic
macrophytes from ponds of the Texas panhandle can be achieved
in a relatively short time (< 2 years) by stocking 7 5 TGC ha""^
(vegetated).
Total eradication of aquatic macrophytes is not always
desirable.
In the case of managing a pond as a sport
fishery, eliminating all aquatic macrophytes would be
detrimental.
With the elimination of macrophytes, epiphytic
45
46
macro-invertebrate diversity and abundance would be reduced,
small fish would become more vulnerable to predation, and
ultimately predators would lack forage (Klussmann et al.
1988).
To avoid total eradication of macrophytes in systems
where partial coverage is desired, Santha (1990) suggested a
single stocking-multiple harvest strategy of TGC. A 6-year
model simulation of a pond in Houston, Texas, indicated that
after stocking 79-130 TGC ha"^ (vegetated), about 40% of the
grass carp needed to be harvested in the second year and 5-8%
of the stocked fish needed to be harvested in subsecjuent
years.
This strategy maintained 40% plant cover in the pond
during a 6-year period.
Application of rotenone at 0.1 mgl — 1
is effective at selectively removing grass carp (Colle et al.
1978) .
In the United States, 24 states currently allow the use
of TGC to control aquatic vegetation.
In Texas, private pond
owners can apply for permits, which would allow them to stock
up to 7 TGC acre"-*- (about 17 ha" ) . This stocking density
considers the total surface area of a pond and not the area
of vegetation within a pond.
The effectiveness of this
stocking density, and all others which are based on total
surface area, is dependent on the abundance of aquatic
macrophytes present at the time TGC are stocked.
Moreover,
the effectiveness of any stocking density will vary across
47
different climatic regions, and thus the use of TGC as
management tool should be applied accordingly.
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53
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F i n a l Project Report.
APPENDIX
PERCENT MACROPHYTE COVERAGE, WATER TRANSPARENCY,
AND WATER TEMPERATURE FROM MAY 1991 TO SEPTEMBER 1992
IN PONDS STOCKED WITH TRIPLOID GRASS CARP
54
55
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58
Table 15.
Water transparency measurements (cm) from
March 1991 tc) September 1992 in ponds that were
initially void of vegetation when triploid grass
carp were stocked at 25 (Low=L), 50 (Medium=M),
and 75 (High=H) ha"!.
Pond
Date
Month
L-10
M-11
H-12
05/91
06/91
07/91
08/91
09/91
02
03
04
05
06
35.0
25.0
20.0
22.0
28.0
25.0
28.0
18.0
22.0
28.0
30.0
30.0
25.0
34.0
31.0
10/91
11/91
01/92
02/92
03/92
07
08
10
11
12
29.0
57.7
76.0
60.0
40.0
31.0
44.0
69.0
61.0
48.0
37.0
61.9
112.0
61.0
86.0
04/92
05/92
06/92
07/92
08/92
09/92
13
14
15
16
17
18
36.0
25.0
21.0
21.0
28.0
15.0
38.0
25.0
26.0
23.0
24.0
13.0
55.0
38.0
39.0
28.0
29.0
15.0
59
Table 16.
Temperatures (°C) from May 1991 to September 1992
of ponds that were initially void of vegetation
when triploid grass carp were stocked at 25
(Low=L), 50 (Medium=M), and 75 (High=H) ha"!.
Pond
Date
Month
L-10
M-11
H-12
05/91
08/91
09/91
02
05
06
21.5
27.0
14.0
21.5
27.5
14.9
19.7
27.5
14.4
10/91
11/91
01/92
02/92
03/92
07
08
10
11
12
17.9
8.5
6.1
10.0
13.6
12.8
8.9
5.0
11.5
13.6
17.0
8.2
6.1
11.0
13.2
04/92
05/92
06/92
07/92
08/92
09/92
13
14
15
16
17
18
20.2
17.0
25.1
25.1
25.8
11.8
18.7
16.6
25.2
25.3
25.3
11.9
19.1
16.2
25.0
25.5
24.5
12.0
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