Download (Phase I), James Bay region, Quebec

Changes in fish populations affected by the
construction of the La Grande complex
(Phase I), James Bay region, Quebec
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Jean-Claude DesLandes, Sylvie Guenette, Yves Prairie,
Dominique Roy, Richard Verdon, and Rejean Fortin
Abstract: Catches per unit of effort (CPUE) with experimental gill nets, recruitment, growth, and
condition were monitored between 1977 and 1992 to evaluate the impact of impoundment on the main
fish species of La Grande 2, Opinaca, and Caniapiscau reservoirs and the Boyd-Sakami diversion.
CPUE and recruitment of northern pike (Esox lucius) and lake whitefish (Coregonus clupeaformis)
increased markedly at most stations after impoundment and decreased at the end of the series. The lake
whitefish and cisco (Coregonus artedii) showed their most striking rise in CPUE at two bay stations of
La Grande 2 and Opinaca reservoirs. CPUE and recruitment of the longnose sucker (Catostomus
catostomus), white sucker (Catostomus commersoni), and lake trout (Salvelinus namaycush) (Caniapiscau)
showed a general decrease following impoundment. CPUE for the walleye (Stizostedion vitreum) also
decreased at several stations; however, the two most southerly stations in La Grande 2 reservoir and the
Boyd - Sakami station showed high CPUE during the series. Concentration- redistribution phenomena
explain part of the observed variations in CPUE. Correlation analyses showed that walleyes and white
suckers were attracted to the warmer, more turbid stations, and that the high primary and secondary
productivity of bay stations attracted the coregonines. Growth and condition of the main species
increased during variable time intervals after impoundment and decreased at the end of the series.
RCsumC : Les captures par unite d'effort (CPUE) au filet maillant experimental, le recrutement, la
croissance et la condition ont CtC suivis entre 1977 et 1992 afin d'kvaluer l'impact de la mise en eau sur
les principales espkces de poissons des reservoirs La Grande 2, Opinaca et Caniapiscau et du dktournement
Boyd-Sakami. Les CPUE et le recrutement du Grand Brochet (Esox lucius) et du Grand CorCgone
(Coregonus clupeaformis) ont fortement augment6 h la suite de la mise en eau, pour diminuer en fin de
sCrie. Le Grand CorCgone et le Cisco (Coregonus artedii) de lac ont connu leurs plus fortes hausses de
CPUE aux deux stations de baie des rCservoirs La Grande 2 et Opinaca. Les CPUE et le recrutement
du Meunier rouge (Catostomus catostomus), du Meunier noir (Catostomus commersoni) et du Touladi
(Salvelinus namaycush) (Caniapiscau) ont connu une baisse gCnCralisCe h la suite de la mise en eau. Les
CPUE du DorC jaune (Stizostedion vitreum) ont aussi diminuC h plusieurs stations; toutefois, les deux
stations situCes le plus au sud dans le rCservoir La Grande 2 et la station du dktournement Boyd-Sakami
ont affichC des CPUE ClevCes pendant la sCrie. Des phCnomknes de concentration-redistribution
expliquent en partie les variations de CPUE observCes. Des analyses de corrClation ont rCvC1C que le
DorC jaune et le Meunier noir se concentrent aux stations les plus chaudes et les plus turbides, alors que
la productivitC primaire et secondaire ClevCe des stations de baie attire les corCgoninCs. La condition et
la croissance des espkces principales a augment6 pendant une pCriode de temps variable h la suite de la
mise en eau, pour diminuer en fin de sCrie.
Introduction
Several studies have addressed the problem of the effects of
impoundment and river diversion on fish populations. The
Received March 2 1, 1995. Accepted June 28, 1995.
J.-C. DesLandes, S. GuCnette, Y. Prairie, and R. Fortin.
DCpartement des Sciences biologiques, UniversitC du Quebec
h MontrCal, C.P. 8888, succursale Centre Ville, Montreal,
PQ H3C 3P8, Canada.
D. Roy. SociCtC d'Energie de la Baie James, 500 Boulevard
RenC-LCvesque Ouest, Montreal, PQ H2Z 1Z9, Canada.
R. Verdon. Hydro-QuCbec, vice-prCsidence Environnement,
75 Boulevard RenC-LCvesque Ouest, Montreal,
PQ H2Z lA4, Canada.
Can. J. Zool. 73: 1860- 1877 (1995). Printed in Canada / IrnprirnC au Canada
Southern Indian Lake impoundment and Churchill River
diversion (northern Manitoba) were the object of several major
publications in the late 1970s and early 1980s. Volume 4 1,
No. 4, of the Canadian Journal of Fisheries and Aquatic
Sciences, published in 1984, presents a series of papers on
the impacts of this hydroelectric project, some of which are
cited below. International symposia have focused on reservoir ecology and management (see, among others, Campbell
et al. 1982). The present study differs from previous ones on
northern reservoir fisheries in several key features related to
general environmental characteristics, composition of the
fish communities, and objectives of the research. Contrary to
the Southern Indian Lake system, there were no major shoreline erosion and sedimentation problems in the La Grande
DesLandes et al.
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complex (James Bay region, Quebec). Also, the rise in water
levels and the area of flooded terrestrial habitat were much
more important in the La Grande complex. Moreover, the
fish communities differ in composition between the eastern
and western part of the complex; they also differ from the
fish communities in other northern reservoirs. Therefore, the
impact of impoundment on the fish communities in environments affected by the development of the La Grande complex
could not readily have been predicted from the results of
previous studies. Most fisheries studies related to reservoirs
in Canada have focused on the effects of impoundment on
major commercial and sport fish species (lake whitefish,
Coregonus clupeaformis; walleye, Stizostedion vitreum; northem pike, Esox lucius; lake trout, Salvelinus namaycush) . The
present study differs by addressing changes in populations of
all major species vulnerable to experimental gill nets over a
prolonged time series covering 1-2 years before and 7 14 years after impoundment.
Phase I of the La Grande complex is one of the largest
hydroelectric projects constructed in Canada. It involves a
series of reservoirs and modified-flow environments covering a total area of 13 520 km2. To quantify changes in the
various compartments of the modified ecosystems, an environmental monitoring program was initiated in 1977- 1978
and is still ongoing for some compartments. Our objective is
to report on the changes of the fish populations in three
reservoirs (La Grande 2, Opinaca, and Caniapiscau) and in
one increased-flow environment (the Boyd - Sakami diversion). Changes in relative abundance (catches per unit of
effort, CPUE) , year-class strength, growth, and condition of
the main fish species will be reviewed. The covariations
between changes in CPUE, water quality, chlorophyll a concentration, and zooplankton biomass will also be presented.
Interpretation of results will focus on distinguishing between
fish concentration-redistribution phenomena in response
to environmental changes and variations in recruitment in
explaining the changes in relative abundance of the more
important species.
General description of the La Grande
complex (Phase I)
Three generating stations were built along La Grande Rivikre
(Fig. 1): La Grande 2, La Grande 3, and La Grande 4. Each
has a corresponding reservoir, the oldest being La Grande 2
(maximum area 2835 km2; mean annual drawdown 3.3 m;
mean depth 22 m; impounded November 1978 - December
1979), located downstream from the other two. To increase
flows in the La Grande Rivikre, three rivers were diverted.
To the south, the Eastmain and Opinaca rivers were cut off
in 1980 to create the Opinaca reservoir (maximum area
1040 krn2; mean annual drawdown 3.6 m; mean depth
8.2 m; impounded April-September 1980), which flows
into the La Grande 2 reservoir via the Boyd - Sakami diversion. The increase in level relative to natural conditions in
the diversion was approximately 2 m. During the years following impoundment, a 2°C increase in mean water temperature and a 2-m decrease in transparency (from 3.5 m in
1978 to 1.5 m in 1981) were observed in the diversion. To
the east, the northward-flowing Caniapiscau River was cut
off in October 1981 to create Caniapiscau reservoir (maximum area 4275 km2; mean annual drawdown 2.1 m; mean
depth 16.8 m; impounded October 1981 - September 1984),
the largest in the complex, which drains into La Grande 4
reservoir via the Laforge diversion.
Three reservoirs (La Grande 2, Opinaca, Caniapiscau),
two increased-flow environments (Boyd - Sakami diversion,
La Grande Rivikre), and two decreased-flow environments
(Eastmain and Caniapiscau rivers) were targeted for the
monitoring program (Bachand and Fournier 1977). Stations
that were to be sampled over the years were established on
a reasoned choice basis, near shore (0 - 5 m), in contrasted
habitats, and in each of the selected environments. A detailed
physical description of the stations can be found in Dussault
and Boudreault (1981). The present paper focuses on fish
population changes in the three reservoirs and in the BoydSakami diversion.
Five stations were sampled from 1978 to 1992 in La
Grande 2 reservoir. Before impoundment, three of these
stations (G2 403, G2 404, G2 405; Fig. 1) were located in
lakes and two in rivers (G2 400, G2 406). Two stations in
La Grande 2 reservoir (G2 404 and G2 406) were eventually
affected by major modified tributaries (the Boyd-Sakami
diversion and the outlet from La Grande 3 reservoir). Station
G2 405 is located in a protected bay, while the other two
stations are located close to the main body of the reservoir.
One site in nearby Detcheverry lake (SB 400; Fig. 1) was
also sampled as a reference station. Waters in the main body
of Opinaca reservoir flow north, whereas there is no measureable flow in protected bays. The four stations in Opinaca
reservoir are compared with one reference station in Rondde-Poele Lake (EA 302). Station EM 401 (lentic before
impoundment) is located in a shallow, protected bay, while
the other three (EM 402, lentic before impoundment; EM 400
and EM 403, lotic; Fig. 1) are located in the main body of
the reservoir along the flow gradient. Only three stations
were sampled throughout the series in Caniapiscau reservoir:
one in the southwestern branch (CA 4.13; Fig. 1) and two in
the northeastern branch (CA 4 11 and CA 4 16); all three were
located in lakes before impoundment. Lakes Nouveau and
Hazeur served as reference stations. Only one station, located
outside the main flow channel, was sampled in the BoydSakami diversion (SK 400; Fig. 1).
Materials and methods
Data collection
In the western section of the La Grande complex (La Grande 2
and Opinaca reservoirs, Boyd-Sakami diversion), the fish
communities were sampled annually from 1977 or 1978 to
1984 and in 1988 and 1992. The eastern section (Caniapiscau
region) was sampled in 1980, 1981, 1982, 1987, and 1991.
Sampling occurred monthly from June to SeptemberOctober, five times per season in the western section of the
complex and four times per season in the eastern section. All
samplings were performed using four multifilament gill nets
45.7 m in length x 2.4 m in depth, set in pairs, a net of uniform 7.6- or 10.2-cm stretched mesh attached to an experimental gill net (stretched mesh ranging from 2.5 to 10.2 cm).
Each pair of nets was set perpendicular to and near the shore.
During impoundment of La Grande 2 reservoir (1979), nets
were set at an angle from surface to bottom to avoid submerged trees. Each sampling period lasted 48 h until 1982
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1862
Can. J. Zool. Vol. 73, 1995
DesLandes et al.
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and 24 h from 1983 on. When the effort lasted 48 h, the nets
were nevertheless visited every 24 h.
The fish caught were counted, measured, and weighed.
For a given day and station, catches of the four nets were
averaged and expressed as numbers of fish per net-day , i .e.,
catches per unit of effort (CPUE). For each species and
station, the four or five monthly CPUE values were averaged
to obtain the mean seasonal CPUE for a given year. Fish
aged as part of a mercury-monitoring program in the same
environments (Brouard et al. 1990) were used to construct
age-length keys and to study variations in growth.
Changes in water quality and chlorophyll a concentration
in the photic zone (0- 10 m) were monitored at the same
stations starting in 1978, along with those of zooplankton
biomass in the water column (0 -25 m maximum) from 1978
to 1984. Details of the methodology used in the collection
and analysis of these data were presented by FrCchette (1978,
1980).
Data analyses
CPUE
For two reservoirs (La Grande 2 and Opinaca), changes in
CPUE for each of the principal fish species were first studied
using univariate repeated-measures analysis of variance
(Freund et al. 1986), which provides an overall indication
of variations over time and between stations. ANOVAs and
Kruskal-Wallis tests were used to detect possible interannual differences in CPUE at the various stations.
To better understand variations in relative abundance for
a given species and environment, CPUE were also computed
for two size groups, each representing 50% of all specimens
caught over the time series. We would expect an increase in
recruitment to show up first in CPUE of small specimens and
later in those of larger specimens. Phenomena associated
with fish concentration -redistribution would likely affect
CPUE of both size groups simultaneously. These results
were presented in detail by DesLandes (1994). Only the main
features are highlighted here.
Parametric correlation analyses were used to determine
relationships between CPUE of the main fish species and
environmental variables (biomass of the main zooplankton
taxa, chlorophyll a concentration, and various physicochemical parameters: dissolved oxygen concentration, temperature, transparency, total phosphorus level, conductivity,
pH). The analyses were performed on yearly averages of the
variables to avoid interference from seasonal phenomena and
thus emphasize annual and interstation variations.
Year-class strength, growth, and condition
Johnson's (1957) year class strength index (YCSI) was used
to quantify recruitment. The index is obtained by dividing the
sum of the annual contributions (percentage of catches) for
a given year class by the sum of the annual contributions for
an average year class at the corresponding ages. Calculations
were made for the longnose sucker (Catostomus catostomus)
lake whitefish, northern pike, and walleye when sample sizes
over the series in a given environment were important enough
to justify them. To generate the indices, we used the agefrequency data from the mercury program (Brouard et al.
1990) to generate age-length keys that were applied to the
length-frequency histogram of catches made in the corresponding year by the environmental monitoring program.
The age-frequency distributions thus generated were used to
calculate the YCSI. Trends in recruitment were also inferred
from the percentage of small specimens in yearly lengthcomposition data ( < 250 mm for whitefish, catostomids,
and walleyes; < 150 mm for ciscoes (Coregonus artedii);
<350 mm for northern pike).
Samples from the mercury program were also used to
study interannual variations in growth in length of the four
species already mentioned, by comparing average sizes at
age of capture. Changes in the Fulton condition index in
modified and reference environments were studied using
only individuals of the most represented length classes for
each species, to eliminate the effects of interannual variations
in length distribution. Length classes used in the calculations
were 100 -200 mm for ciscoes, 400 - 600 mm for walleyes
and lake trout, 300 - 500 mm for longnose suckers, white
suckers (Catostomus commersoni), and lake whitefish, and
500-700 mm for northern pike. For the various species,
ANOVAs and Student - Neuman - Keuls tests were used to
compare annual means for a given environment and between
modified and reference environments.
Results
Trends in CPUE for the main species
La Grande 2 and Opinaca reservoirs and Boyd-Sakami
diversion
Under natural conditions, catches in the lentic and lotic environments incorporated in La Grande 2 (Fig. 2) and Opinaca
reservoirs (Fig. 3), in the Boyd- Sakami Diversion (Fig. 4)
and catches in reference lakes in the western part of the
La Grande complex (not illustrated) were generally dominated by walleyes, followed by lake whitefish, longnose and
white suckers, northern pike, and ciscoes. The order of
importance of the last five species varied somewhat between
the various environments. Burbot (Lota lota), lake trout,
yellow perch (Perca flavescens), lake sturgeon (Acipenser
jidvescens), round whitefish (Prosopium cylindraceum),
spottail shiners (Notropis hudsonius), trout-perch (Percopsis
omiscomaycus), and lake chub (Couesius plumbeus) were
also gill-netted in relatively small numbers in the three water
bodies. Other secondary species include the pearl dace
(Semotilus margarita; La Grande 2 and Opinaca reservoirs),
brook charr (Salvelinus fontinalis; La Grande 2 reservoir),
and fallfish (Semotilus corporalis; Opinaca reservoir).
Globally, the secondary species, including burbot and lake
trout, represented less than 6 % of the catches under natural
conditions and their contribution became negligible over
the years.
For each of the two western reservoirs, repeated-measures
analyses of variance performed on mean CPUE over the five
(La Grande 2) and four stations (Opinaca) sampled throughout the series revealed significant changes over time ( p <
0.05) for the six main species (walleye, both coregonines,
both catostomids, and northern pike). However, trends over
time varied significantly ( p < 0.05) between stations for
these species, except for the cisco in La Grande 2 reservoir
and the two catostomids in Opinaca reservoir.
1864
Can. J. Zool. Vol. 73, 1995
Fig. 2. (A-F) Trends in mean annual CPUE of the main species at the various stations in La Grande 2 reservoir, including global
mean CPUE (stations regrouped), from 1977 to 1992; * and k: interannual differences ( p < 0.05) in mean CPUE detected by
ANOVAs (*) and Kruskal-Wallis tests (k). (G and H) Trends in YCSI (1976- 1986) and percentage of small specimens in total
catches (1978 - 1992). The arrow below the abscissa indicates the year of impoundment.
Longnose sucker
12
n
>
-
--------- --
10
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03
'73
&a
G2400 *k
-
G2403 *k
-----=
Mean
6
0
-----
G2404*k
G2405*k
-
w
5
White sucker
G2400
G2403 *k
G2404*k
G2405*k
- 9
*
*
Mean
V
LU
3
4
a
0
2
0
77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92
t
77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92
t
Year
El
-------- --
Cisco
--------
-- --
-
G2400
G2403 *k
Lake whitefish
G2400 *k
G2403
---G2404
G2404
-
G2405
G2406
Mean
Year
*
G2405*k
a
a
a
G2406 *k
Mean
;
;
*
0-
'
'
-0
-0
-0
0
77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92
77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92
t
El
t
Year
EI
Northern pike
12
Year
Walleye
-
\
h
>
10-
--
A
1 \
\
\
--------
M
77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92
t
Year
0 -
G2400 k
G2403 k
G2404 k
G2405
e
a
--
*
n
*
77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92
t
Year
DesLandes et al.
Fig. 2 (concluded).
Year class strength index
"I
--
3,o
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% small specimens
16 %
76
77
78
79
80
81
82
------
---
14 %
Longnose sucker
White sucker (1)
Walleye (I)
Lake whitefish
Northern pike
83
84
85
78 79 80 81 82 83 84 85 86 87 88 89 90 91 92
86
t
Year class
Year
Table 1. Parametric correlations (Pearson's correlation, r, and and probability level) computed between mean summer CPUE of the
principal species and mean summer values of environmental variables at the various stations in La Grande 2 and Opinaca reservoirs and
at the Boyd -Sakami station.
Longnose
sucker
r
P
White sucker
r
P
Cisco
r
Lake whitefish
P
r
P
Northern pike
r
P
Walleye
r
P
Transparency
Temperature
pH
Phosphorus level
Conductivity
Chlorophyll a concn.
Dissolved oxygen concn.
Copepods
Cladocerans
Rotifers
Total zooplankton
Longnose suckers showed significant ( p < 0.05) interannual differences in mean CPUE at the five stations in
La Grande 2 reservoir, at three of the four stations in
Opinaca reservoir, and at the Boyd - Sakami station (Figs. 2,
3, and 4). Similarly, white suckers showed significant ( p <
0.05) interannual differences in mean CPUE at four of the
five stations in La Grande 2 reservoir, at three of the four
stations in Opinaca reservoir, and at the Boyd-Sakami
station.
Because the 1980 increase in CPUE of both catostomids
at station G2 404 in La Grande 2 reservoir (Fig. 2) and at
station EM 402 in Opinaca reservoir (Fig. 3) involved both
large and small specimens (DesLandes 1994), it is interpreted as a change in concentration in response to environmental changes (beginning of operation of the Boyd - Sakami
diversion in the case of G2 404). However, the decrease in
CPUE of both catostomids at most stations of the two reservoirs at the end of the series to values globally lower than initial ones indicates major recruitment problems. Longnose
sucker YCSI values in La Grande 2 reservoir were higher in
1978- 1979, before and during impoundment; they declined
afterwards (Fig. 2). The proportion of <250 mm white
suckers in the catches has been very low since 1979 (Figs. 2
and 3). At the Boyd - Sakami station, the sharp rise in longnose sucker CPUE began coincidentally with the diversion
and continued in the following year. Catches then fell but
remained well above prediversion levels (Fig. 4). However,
the proportion of small longnose suckers ( <250 mm) after
the diversion is generally low (Fig. 4) despite the substantial
CPUE observed. Catches of both catostomids were higher in
less transparent waters, as suggested by the significant negative Pearson's correlations, r, ( p < 0.05), observed between
mean seasonal CPUE values at the various stations of the
three modified environments and mean seasonal water transparency (r = -0.26 for longnose suckers and -0.23 for
white suckers; Table 1); however, r values are low and the
relationship cannot be generalized to the Caniapiscau region,
where both water transparency and longnose sucker CPUE
are high. Of the two catostomids, only white suckers showed
a positive significant correlation with water temperature (r =
0.32), suggesting that this species concentrates at the warmer
stations. White sucker CPUE values were also positively
correlated with conductivity (r = 0.28, p < 0.01 ; Table 1).
Lake whitefish CPUE increased at several stations in
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DesLandes et al.
Fig. 3 (concluded).
EI
Year class strength index
% small specimens
80%
------- --
Whae sucker (1)
170%
Longnose sucker (1)
Cisco (2)
--
0
0-
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0
0
0-
0'
0
'
-
'0
'0'
0
'
0
'
I
76
77
78
79
80
83
82
81
85
84
78
86
79
t
Year class
I
I
I
I
80 81 82 83 84 85 86 87 88 89 90 91 92
Year
Fig. 4. (A) Trends in mean annual CPUE of the main species at the Boyd-Sakami station, including global mean CPUE (stations
regrouped), from 1978 to 1992. * and k: interannual differences ( p < 0.05) in mean CPUE detected by ANOVAs (*) and
Kruskal-Wallis tests (k). (B and C) Trends in YCSI (1976- 1986) and percentage of small specimens in total catches (1978- 1992).
The arrow below the abscissa indicates the year of diversion.
El
CPUE
-- ---
12
A
78
79
80
81
t
82
--------
Longnose sucker +k
Cisw
+
-No&ernpiketk
83
84
85
86
87
88
White sucker
ycsl
--
+k
+
Lake whitefish k
Lake whitefish
Northern pike
WaIleye+k
89
90
91
92
n
76
78
79
Year
80
81
Year
t
% small specimens
---
78
79
80
81
t
82
83
84
85
Year
Longn-
sucker
Walbye
86
87
88
89
90
91
92
82
m
84
as
86
Can. J. Zool. Vol. 73, 1995
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La Grande 2 and Opinaca reservoirs and at the BoydSakami station following impoundment (Figs. 2, 3, and 4).
Interannual variations are statistically significant ( p < 0.05)
at four of the five stations in La Grande 2 reservoir, at three
of the four stations in Opinaca reservoir, and at the BoydSakami station (Figs. 2, 3, and 4). However, the pattern of
variation was quite variable between stations and the increase
was greater at the two bay stations (G2 405, Fig. 2; EM 401,
Fig. 3). Lake whitefish CPUE showed significant ( p <
0.05) positive Pearson's correlations with total phosphorus
(r = 0.7; Table I), chlorophyll a concentration (r = 0.51),
and biomass of the various zooplankton taxa (r values varying between 0.21 and 0.46; Table 1); they also showed
negative significant correlations with water transparency
(r = -0.25) and dissolved oxygen concentration (r = -0.3 1).
The high productivity of the bay stations, resulting from high
rates of decomposition of terrestrial vegetation, seems to
attract lake whitefish and is probably responsible for the
significant correlations observed. Concentration phenomena
were also observed at station G2 406 during filling of
La Grande 3 reservoir (in 1981 and 1982). At all stations of
the three environments, lake whitefish CPUE values at the
end of the series were equivalent to or higher than initial
values.
Increased recruitment also explains part of the rise in
whitefish CPUE values over the series. Lake whitefish YCSI
increased in the year of impoundment and gradually declined
over time in both reservoirs and at the Boyd - Sakami station
(Figs. 2, 3, and 4). In Opinaca reservoir, whitefish YCSI
showed significant positive Pearson's correlations (r = 0.9;
p < 0.01) with mean summer cladoceran biomass and with
the mean total zooplankton biomass. Similar correlations
were not observed in La Grande 2 reservoir or at the Boyd Sakami station.
Interannual variations in cisco CPUE were significant
( p < 0.05) at one station in La Grande 2 reservoir (G2 403,
Fig. 2), at three stations in Opinaca reservoir (Fig. 3), and
at the Boyd-Sakami station (Fig. 4). An important rise in
cisco CPUE during the years following impoundment was
observed at the bay stations of both reservoirs (G2 405,
Fig. 2; EM 401, Fig. 3). Cisco CPUE showed significant
positive ( p < 0.05) correlations with total phosphorus level
(r = 0.73), chlorophyll a concentration (r = 0.38), and
biomass of various zooplankton taxa (r values between 0.26
and 0.33), and significant negative ( p < 0.05) correlations
with water transparency (r = -0.25) and dissolved oxygen
concentration (r = -0.35), as was the case for lake whitefish, suggesting that the high productivity of the bay stations
attracts the coregonines. The proportion of < 150-mm ciscoes
was higher from 1978 to 1981 than from 1982 to 1984 (Figs. 2
and 3), suggesting that recruitment may have been higher at
the time of impoundment and declined somewhat since then.
The spectacular increase in the proportion of small specimens in the 1988 and 1992 catches in both reservoirs (Figs. 2
and 3) is chiefly due to a major decrease in the abundance
of large specimens, possibly resulting from concentration redistribution phenomena. At most stations in the three modified environments, cisco CPUE values at the end of the
series were roughly equivalent to initial values.
The northern pike is the only species to show statistically
significant ( p < 0.05) variations over time at all stations
in the three environments. Most stations in the two reser-
voirs showed a general and prolonged rise in CPUE after
impoundment (Figs. 2 and 3). Peak CPUE values, however,
did not occur during the same year at all stations. The
increase in northern pike CPUE was more gradual and less
important at the Boyd -Sakami station (Fig. 4), the peak
occurring in 1988. Unlike ,those of most species, northern
pike catches were generally less abundant at ,the two reservoir bay stations during the first years after impoundment
(G2 405, Fig. 2; EM 401, Fig. 3). The breakdown of CPUE
values into two size groups (DesLandes 1994) suggests that
part of the increase is due to concentration phenomena, particularly at station G2 404 in 1981 (the first year of operation
of the Boyd - Sakami diversion) and at station G2 406 during
filling of La Grande 3 reservoir (198 1, 1982; Fig. 2). Northern pike CPUE values showed a positive, significant correlation with water temperature (r = 0.22, p < 0.05; Table 1)
and chlorophyll a concentration (r = 0.26, p < 0.05) and
a negative, significant correlation with conductivity (r =
-0.25, p < 0.05; Table 1). As was the case for lake whitefish, the rise in northern pike CPUE during the series also
involved increased recruitment. Northern pike YCSI increased
in the year of impoundment in both reservoirs and gradually
declined over time (Figs. 2 and 3). YCSI peaked in 1982 at
the Boyd-Sakami station (Fig. 4) and declined thereafter.
Northern pike CPUE values were decreasing at most stations
in the three environments at the end of the series, but they
were globally equivalent to (reservoirs) or higher than
(diversion) initial values.
Interannual variations in walleye CPUE were statistically
significant ( p < 0.05) at four stations in La Grande 2 reservoir (Fig. 2), at three stations in Opinaca reservoir (Fig. 3),
and at the Boyd -Sakami station (Fig. 4). From 1981 to
1988, more than 94% of walleye catches in La Grande 2
reservoir occurred at the two warmer, less transparent, and
most productive stations, G2 404 (near ,the Boyd - Sakami
diversion) and G2 405 (bay) (Fig. 2), where the fish seem to
concentrate. This partly explains the negative significant
correlation observed between walleye CPUE and water
transparency (r = -0.45, p < 0.001 ; Table 1) and the positive correlation observed with water temperature (r = 0.34,
p < 0.001). Trends in CPUE at stations G2 404 and G2 405
are quite variable, showing a drastic decline in 1979 (year of
impoundment, possible dilution effect) or 1980, followed by
values equivalent to initial ones from 1980- 1981 to 1988,
and by a drastic decline in 1992 (Fig. 2). Three of the four
Opinaca reservoir stations showed a major decline after
impoundment; this nearly instantaneous decrease involved
both small and large individuals, suggesting a redistribution
phenomenon. CPUE values then increased slightly from
1988 to 1992, but were still inferior to initial ones at three
of the four stations in 1992 (Fig. 3). At the Boyd - Sakami
station, interannual variations in CPUE were very pronounced for walleyes, with a peak of 13 fish per net-day
occurring soon after the diversion (Fig. 4). This abrupt rise
in CPUE regardless of size (DesLandes 1994) suggests a sustained concentration phenomenon at the station.
In La Grande 2 reservoir, the proportion of <250-mm
walleyes was high in 1978- 1979 and low or null from 1980
to 1983. The slight increase in this proportion observed from
1984 on could indicate better recruitment, possibly limited to
the southern portion of the reservoir. In Opinaca reservoir,
despite the decline in CPUE following impoundment,
DesLandes et al.
voirs, the proportion of small individuals ( < 350 mm) was
practically null at the three stations throughout the series
(Fig. 5).
Interannual variations in CPUE for lake trout were significant ( p < 0.05) at the two stations in the northeastern
part of the reservoir (CA 4 11 and CA 41 6; Fig. 5), where
CPUE decreased from 3-4 specimens per net-day in 1980
to 0.2 specimen per net-day in 1991. CPUE remained relatively constant at station CA 413. However, the analysis of
CPUE broken down into two size groups (DesLandes 1994)
shows that the apparent stability at station CA 4.13 actually
reveals a decrease in 1620-mm specimens coupled with an
increase in large specimens. Recruitment problems are thus
evident in 1991, small specimens being practically absent
from catches at the three stations.
Caniapiscau Reservoir
The fish community in Caniapiscau reservoir differs from
those in La Grande 2 and Opinaca reservoirs by the absence
of walleyes and ciscoes. Five main species were captured:
lake whitefish, longnose sucker, lake trout, northern pike,
and white sucker. Secondary species include lake chub,
burbot, round whitefish, brook charr, and landlocked salmon
(Salrno salar) .
Station CA416 showed a significant decrease in longnose
sucker CPUE over time, whereas relative stability ( p >
0.05) was observed at the other two stations. YCSI and the
proportion of specimens < 250 mm were higher in 1981 than
in 1982- 1987, suggesting that recruitment decreased after
impoundment (Fig. 5). However, by 1991 the proportion of
small longnose sucker had returned to its 1980 level. The
white sucker was always less abundant than its congener
(Fig. 5). At the two stations where significant interannual
variations were observed, white sucker CPUE peaked in
1981- 1982 (the start of impoundment), before declining
markedly to lower than initial values in 1991.
Interannual variations in CPUE for lake whitefish were
significant ( p < 0.05) at two of the three stations (Fig. 5).
At these two stations, CPUE decreased during the first year
of impoundment (1982), remained low in 1987, and
increased at the end of the series in 1991. The YCSI
increased in 1980, peaked in 1981, and declined following
impoundment (1982- 1985; Fig. 5). The decrease in the
proportion of <250-mm specimens observed in 1987 also
suggests less efficient recruitment. The generalized increase
in CPUE observed in 1991, coupled with the very high
proportion of small specimens, suggests a restoration of
recruitment in the late 1980s. However, this increase in the
proportion of small specimens is partly due to a significant
rise in the proportion of dwarf individuals in the 1991
catches. Dwarf lake whitefish were present in the natural
lakes that were incorporated in Caniapiscau reservoir, but
their contribution to experimental catches increased significantly between the early 1980s and 1991.
Trends in northern pike CPUE were similar at the three
stations in Caniapiscau reservoir. CPUE increased significantly ( p < 0.0001) after impoundment, peaking in 1987,
and decreasing to initial values in 1991 (Fig. 5). The general
increase in CPUE in 1987 was observed mainly in specimens
5680 mm (DesLandes 1994) and was probably related to
increased recruitment at the beginning of impoundment.
However, contrary to what was observed in the other reser-
Growth and condition
In spite of the low annual sample sizes available for the study
of growth, interannual differences were observed between
mean sizes at several ages for the main species in the various
environments, generally between years showing extreme
values. Variations in growth rate following impoundment are
fairly clear in La Grande 2 reservoir (Fig. 6). Growth rates
of longnose suckers, whitefish, pike, and walleyes rose sharply
after impoundment. Thereafter, growth rates declined, mean
sizes at early ages (7 and under) at the end of the series (1988
and 1992) being lower than, or equivalent to, those observed
at the start of the series (Fig. 6). The oldest fish, which
benefited from faster growth rates during their early years,
were still longer, on average, at a given age at the end of the
series.
Generally, all species showed a significant increase ( p <
0.05) in condition factor after reservoir impoundment, with
the exception of whitefish and pike in the Boyd-Sakami
diversion and white sucker and pike in Caniapiscau reservoir
(Fig. 7). The increase in condition factor for the various
species, expressed as percentage of initial values, was practically identical in La Grande 2 and Opinaca reservoirs: longnose sucker, 20.0 vs. 17.9%; white sucker, 13.2 vs. 11.2%;
whitefish, 15.7 vs. 15.7%; cisco, 18.8 vs. 18.5%; northern
pike, 17.5 vs. 20.4% ; walleye, 2 1.3 vs. 24.4 % . However,
the improvement in condition was generally lower in the
Boyd - Sakami diversion: longnose sucker, 5.6 % ; white
sucker, 6.0%; walleye, 6.6 % ; whitefish, no significant
increase. The condition of northern pike in the diversion did
not improve significantly after the increase in flow, but it
declined at the end of the series (1988 - 1992; Fig. 7). In
Caniapiscau reservoir, the improvement in condition was
equivalent to that observed in the other two reservoirs for
whitefish (14.9 %) but lower for longnose suckers (14.4 %).
Lake trout condition increased by 14.3 % . Trends in condition varied from one species to another for a given environment and from one environment to another for a given
species (Fig. 7). However, at the end of the series, most
species in the four modified environments showed mean condition values higher than or equivalent to the initial ones.
Can. J. Zool. Downloaded from www.nrcresearchpress.com by Canadian Science Publishing on 08/12/15
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walleye YCSI was higher from 1981 to 1983 than in preceding years (Fig. 3).
Variations in CPUE were considerably more pronounced
in La Grande 2 and Opinaca reservoirs than at the reference
stations in Detcheverry and Rond-de-Poele lakes (not illustrated). Only walleyes showed significant interannual variations ( p < 0.05) in Detcheverry Lake, as a result of the
increase in catches observed in 1988; however, CPUE for
this species fell sharply in 1992, as in the reservoir. None of
the major species showed significant interannual variations
in CPUE in Rond-de-Poele Lake. In Detcheverry Lake,
CPUE values for the various species were much lower than
in La Grande 2 reservoir throughout the series, whereas the
contrary was observed for several species in Rond-de-Poele
Lake relative to Opinaca reservoir.
Discussion
The small number of stations sampled throughout the series
in each environment, coupled to the fact that stations were
located in contrasted nearshore habitats, on a reasoned
1870
Can. J. Zool. Vol. 73, 1995
Fig. 5. (A-E) Trends in mean annual CPUE of the main species at the various stations in Caniapiscau reservoir, including global
mean CPUE (stations regrouped), from 1980 to 1991. * and k: interannual differences ( p < 0.05) in mean CPUE detected by
ANOVAs (*) and Kruskal-Wallis tests (k). (F and G) Trends in YCSI (1976- 1985) and percentage of small specimens in total
catches (1980- 1991). The arrow below the abscissa indicates the year of impoundment.
4
Longnose sucker
-
White sucker
---
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CA411
h
h
-
-
-- -- --
Mean *k
Mean *k
8 0 8 1 8 2 8 3 8 4 8 5 8 6 8 7 8 8 8 0 9 0 0 1
t
8 0 8 1
Year
El
Lake whitefish
---- --
Northern pike
CA411 *k
CA413
CA416*k
25-
\
-.,\
-
8 2 8 3 8 4 8 5 8 6 8 7 8 8 8 0 9 0 9 1
t
Year
30-
C M l l *k
CA413
CA416 k
I
8 0 8 1
I
0
I
I
I
l
I
I
I
I
l
I
8 2 8 3 8 4 8 5 8 6 8 7 8 8 8 9 9 0 9 1
t
8 0 8 1
8 2 8 3 8 4 8 5 8 6 8 7 8 8 8 0 9 0 0 1
t
Year
4
Year
Lake trout
-
--- --
0
0
CA416*k
CA413
CA411 *k
Mean *k
-
- - - 0 - - - - -
0
80
l
l
r
l
l
l
f
l
l
l
l
81
82
83
84
85
86
87
88
89
90
91
t
Year
DesLandes et al.
Fig. 5 (concluded).
El
Year class strength index
-
70
Lake whitefish
*-
-
% small specimens
-
Longnow sucker
50-
Longnosesucker
---
Lake whitefish
Northern pike
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a,
4-
40-
C
2 30a
I
76
77
1
1
I
I
1
I
I
1
78
79
80
81
82
83
84
85
Year
*
choice basis, precludes any quantitative extrapolation of our
results to the fish communities as a whole. However, such
was not the initial objective of the environmental monitoring
network. Given the size of the modified environments, the
cost of applying a sampling strategy that would have provided adequate coverage of all the major habitats in each
reservoir would have been prohibitive.
Instead, the importance and generality of the changes in
CPUE and recruitment observed in this study were inferred
qualitatively from the comparison of trends between stations
in a given environment and between modified environments
showing the same general characteristics (La Grande 2 and
Opinaca reservoirs, the Boyd - Sakami diversion). Moreover, by being located in relatively shallow nearshore areas,
our sampling stations address most of the major components
of the fish community because benthic and fish production in
these northern oligotrophic environments is concentrated in
relatively shallow habitats (Dumont 1977; Johnson 1975).
The fact that the major changes in CPUE and recruitment
observed in the modified environments did not occur in
nearby reference lakes supports the interpretation that they
were related to impoundment.
Although the impoundment of the various environments
studied occurred 12 - 16 years ago, the dynamics of the various species is still changing. Important variations in relative
abundance were still being observed in 1991 for lake whitefish and northern pike in Caniapiscau reservoir. We may
expect further changes in the various environments, related
to short- and long-term water level manipulations, which may
affect recruitment success of the various species, predator prey relationships, availability of proper spawning grounds
for species using nearshore hard substrates, etc. The environmental monitoring network is still ongoing to follow these
changes, although with longer intervals between samplings
(2 -4 years).
CPUE and recruitment of the main species
Catostomids
As already mentioned, the negative correlation between longnose and white sucker CPUE and water transparency should
20
-
10
-
----
o - b - - - - - - -
80
81
82
t
83
84
85
86
87
v
88
-
m
89
.
90
1
91
Year
be interpreted with caution in view of the high longnose
sucker CPUE observed in the transparent waters of Caniapiscau reservoir. However, the positive correlation between
white sucker CPUE and water temperature probably reflects
a preference for warmer waters (bays, shallow areas of lakes
and reservoirs) at these latitudes (Boucher and Roy 1985).
The white sucker showed CPUE values higher than those of
its congener only in warmer environments (Opinaca reservoir at the beginning of the series, Rond-de-Poele Lake). The
white sucker's difficulties in Caniapiscau reservoir are possibly related to the marked decline in mean temperatures over
the summer after impoundment.
The lack of adequate spawning grounds for catostomids
cannot explain the difficulties experienced by both species at
most stations in La Grande 2 and Opinaca reservoirs, because
several good-quality spawning tributaries are available (Skguin
et al. 1978a, 1978b; Boucher and Roy 1985). Their decline
could be due to the marked increase in abundance of whitefish and northern pike, leading to competition among benthivores and (or) to increased predation by northern pike.
Competition among benthivores would be more likely to
involve the younger stages, because older juveniles and adult
longnose suckers and whitefish showed sharp increases in
growth rate and condition factor following reservoir
impoundment. Increased predation following the rise in
northern pike abundance could lead to decreased sucker
abundance: the introduction of northern pike was indeed
effective in controlling the abundance of longnose and white
suckers in Eleven Mile Lake reservoir (Cook and Bergersen
1988). The competition -predation hypotheses do not explain
the fact that the longnose sucker maintained relatively high
CPUE after the impoundment of Caniapiscau reservoir. The
general difficulties experienced by both catostomids in
several reservoirs in Quebec need to be investigated further.
Lake whitejish
Bay stations of La Grande 2 and Opinaca reservoirs concentrated lake whitefish over most of the series, probably
because of their high general productivity. In Great Bear
Lake (Northwest Territories, Canada), lake whitefish are
restricted to bays, where they are rarely captured deeper than
1872
Can. J. Zool. Vol. 73. 1995
Fig. 7. Interannual variations in Fulton's condition index (K) for the various species in the four modified ecosystems and in the
reference lakes during the years indicated. The arrow below the abscissa indicates the year of impoundment. For the various species,
"R" denotes samples from a reference lake.
Fig. 6. Interannual variations in growth of longnose suckers, lake whitefish, northern pike, and walleyes from La Grande 2
reservoir (n is the sample size), during the years indicated. *, interannual differences ( p < 0.05) in mean total length at capture at
a given age. Only the initial and final sampling years and one or two intermediate ones are illustrated.
Can. J. Zool. Downloaded from www.nrcresearchpress.com by Canadian Science Publishing on 08/12/15
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Longnose sucker
Age (years)
Northern pike
Age (years)
20 m; the distribution of species in this oligotrophic lake is
related to the density of benthic organisms (Johnson 1975).
A similar situation was observed in Detcheverry Lake (reference lake for La Grande 2 reservoir), where lake whitefish
were rarely captured deeper than 5 m (Dumont 1977).
The fact that lake whitefish CPUE values were much
higher at the bay stations of La Grande 2 and Opinaca reservoirs explains the rather unusual negative correlation with
water transparency that was observed. However, the slightly
lower values of this variable at the bay stations (ca. 2.25 m
at G2 405 and ca. 1.7 m at EM 40 1) than at the other stations
sampled are not considered limiting for this species. The
relatively high transparency values observed at most of the
Lake whitefish
Age (years)
Walleye
Age (years)
reservoir stations and in the Boyd -Sakami diversion, which
for the most part are located outside of the zone of glaciomarine and glacio-lacustrine silts and clays, are probably
partly responsible for the success of the species in these
systems.
Differential movements in response to changes in local
conditions after impoundment explain part of the variations
in whitefish CPUE observed in this study. However, increased
recruitment was also involved. The rapid but short-term
increase in recruitment was probably due to the general
increase in primary and secondary production following
impoundment, as suggested by the positive correlation
between YCSI and zooplankton biomass in Opinaca reser-
BesLandes et al.
La Grande 2 reservoir
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Longnose sucker (n = 1693)
Longnose sucker (n = 1881,R
White sucker (n = 1413)
Whitefish (n = 3500)
Cisco (n = 989)
Cisco (n = 1 07),R
Northern pike (n = 2392)
Walleye (n = 1823)
WaDleye (n = 383),R
5
0.9
78 80 82 84 86 88 90 92
0.5
78
Year
4
86 82 84 86
88 90 92
Year
4
Opinaca reservoir
Longnose sucker (n = 482)
- - - White sucker (n = 1251)
- - - Whitefish (n = 2997)
-Whitefish (n
= 978),R
---
Cisco (n = 1060)
Cisco (n = 388),R
N o b e r n pike (n = 1562)
Northern pike (n = 516),R
Walleye (n = 2228)
Walleye (n = 701),R
- * - - -- -. -- -- -5
4
t
78
0.5
78 80 82
80 82 84 86 88 90 92
84
86
88 98
92
Year
4
Year
Boyd-Sakami diversion
Longnose sucker (n = 912)
= 246)
= 249)
sucker (n
-- --- --- White
White sucker (n
-
Y
- - .- -- --
0.8
Cisco (n = 75)
Cisco (n = 257),R
Northern pike (n = 234)
Nortern pike (n = 143,R
Walleye (n = 1273)
Y
-
Whitefish (n = 570)
Whitefish (n = 718),R
0.7
-- - Walleye (n = 4811,R
0.6
----0.8
-I
$8 8Q 82 84 86 88 98 92
5
0.5
78
80 82 84 86
Year
88 90 92
Year
Caniapiscau reservoir
- ---
Longnose sucker (n = 1415)
White sucker (n = 304)
Whitefish (n = 2489)
Whitefish (n = 281),R
-
---
0.8
80
82
84
86
Year
88
90
78
82
84
86
Year
88
9092
Northern pike (n = 318)
- - Lake trout (n = 1 TI),R
Lake trout (n = 362)
Can. J. Zool. Vol. 73, 1995
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voir. Although several authors use the same explanation for
the increase in whitefish recruitment in reservoirs (Machniak
1975a), few present quantitative data relating year-class
strength and indices of secondary production.
Lake whitefish tend to concentrate at the mouth of tributaries during the fall, and also immediately downstream of
La Grande 3 power station (Boucher and Roy 1985), in the
lower part of the Coutaceau River rapids (station G2 404),
and along dikes (Lalumikre and Dussault 1992), probably in
preparation for spawning. In Outardes-2 reservoir, the only
identified spawning ground is located immediately downstream of Outardes-3 power station (Gendron 1988; Fortin
and Gendron 1990), in relatively swift waters. The eggs
either remain in the deeper part of the canal or drift over long
distances in deeper water, which may prevent the negative
effects of a winter drawdown. The fact that whitefish in
La Grande 2 reservoir did not show a marked decrease in
recruitment following the very substantial winter 1982 drawdown (8 m), as well as the lack of correlation, for the available series, between year-class strength and winter drawdown,
suggest that eggs are deposited at sites where they are not
affected by fluctuations in water level. Gendron (1990, 1991)
found no significant relationship between winter drawdown
and whitefish year-class strength in Outardes-4, Pipmuacan,
and Baskatong reservoirs. However, in Cross Lake
(Churchill-Nelson complex), a rather shallow lake, where
ciscoes and whitefish spawn on reefs and off rocky points in
the lake (Ayles 1976), year-class strength was negatively
correlated with winter drawdown (Bodaly et al. 1984; Gaboury
and Patalas 1984).
Another factor that may explain the increase in whitefish
recruitment after impoundment in the La Grande complex is
the rise in grow.th rates and condition, which may have been
responsible for a general increase in potential fecundity of
the populations (Healey 1978). However, higher growth
rates may have introduced a positive bias in the evaluation of
year-class strength, the fish becoming vulnerable to the fishing gear at younger ages.
The late increase in lake whitefish CPUE at the three
stations in Caniapiscau reservoir (1991) compared with
La Grande 2 and Opinaca reservoirs may have resulted from
interactions with northern pike. The minimal proportion of
<250-mm specimens in 1987 coincides with the highest
northern pike CPUE of the series, and the maximal 1991
proportion with the lowest northern pike CPUE. Predation
by northern pike may have suppressed whitefish abundance
during the first years after impoundment. The presence of
cisco in the western reservoirs may have tempered the impact
of northern pike predation on whitefish. As mentioned
earlier, the rise in the proportion of dwarf lake whitefish in
the 1991 catches (ca. 50%) also contributed to the increase
in the proportion of small specimens at the end of the series.
Cisco
As already mentioned for lake whitefish, the important
catches of ciscoes at the two highly productive bay stations
are largely responsible for the negative correlations observed
with water transparency and dissolved oxygen concentration,
and for the positive correlations with total phosphorus level,
chlorophyll a concentration, and biomass of the various zooplankton taxa. A negative correlation between cisco CPUE
and water transparency was also mentioned by Beauvais
(1977)' for lakes in Quebec's James Bay region. Given the
proximity to shore of the stations sampled in this study, and
the lack of stations sampling the pelagic zone, the cisco is
probably the species for which our CPUE results are least
representative. The importance of the cisco in the diet of
northern pike at the end of the series in La Grande 2 reservoir (R. Verdon, unpublished data) suggests that CPUE
underestimates the abundance of this important species.
More studies are required to better understand the dynamics
of the cisco in the La Grande complex.
Northern pike
A general increase in northern pike CPUE was observed
after impoundment at practically all stations sampled in this
study. While at the start of the series, the northern pike often
ranked second among predators, behind the walleye (westernsector reservoirs) or lake trout (Caniapiscau reservoir),
it became the dominant predator only a few years after
impoundment.
The lesser occurrence of northern pike in reservoir bay
stations in the western sector remains unexplained. It may
have been associated with the lower water transparency in
these sectors. Several authors mention that water transparency may affect the choice of habitat by this species
(Moreau and Legendre 1979; Chapman and Mackay 1984;
Cook and Bergersen 1988). However, our study did not
reveal a significant relationship between northern pike CPUE
and water transparency, and this factor did not prove critical
for the survival of the species within the range of values
encountered in our study.
Although major concentration -redistribution phenomena
were involved, the increase in northern pike CPUE at reservoir stations and the Boyd -Sakami station was also dependent on a widespread increase in recruitment, as revealed by
the analysis of YCSI. As has often been mentioned in the
literature (Machniak 1975b), the improvement in recruitment
was probably due to the increase in available spawning and
nursery habitat related to the rise in water levels. The general
increase in zooplankton production following impoundment
observed in this study may also have been an important factor affecting recruitment. Submerged trees, which in certain
areas develop an abundant growth of periphyton, offer habitat conditions similar to macrophyte beds, and possibly contribute to increased survival of juveniles by providing food
and cover. High recruitment values were observed for at
least 3 years in the two western reservoirs and the BoydSakami diversion, i.e., for a somewhat longer period than at
Wupaw Bay, Southern Indian Lake, where they lasted only
1 year (Bodaly and Lesack 1984; Strange et al. 1991) following rapid degradation of the submerged vegetation.
Northern pike CPUE decreased in most of the environments at the end of the series, particularly in Caniapiscau
reservoir, where water levels fell regularly between 1986
and 1990. The sequence of increased pike abundance and
recruitment after reservoir impoundment, followed, after a
variable number of years of operation, by decreased abunA. Beauvais. 1977. Niches et associations de poissons dans
les lacs de la Radissonnie quCbCcoise. Une Ctude effectuCe
pour le compte de la SociCtC d'Cnergie de la Baie James.
Centre de recherche en sciences de I'environnement,
UniversitC du Quebec a Montreal (PolycopiC).
DesLandes et al.
dance and recruitment has been documented by several
authors (Machniak 1975b).
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Walleye
At the beginning of the series, the walleye was the dominant
predator in most of the environments incorporated in the
La Grande 2 and Opinaca reservoirs. Its CPUE subsequently
fell at the majority of stations following impoundment.
Thereafter, more than 94 % of walleyes caught in La Grande 2
reservoir came from the two warmer and more turbid stations. The Boyd -Sakami station also showed high CPUE. In
La Grande 2 reservoir, the decrease in the proportion of
small specimens from 1980 on suggests that recruitment
started declining shortly before the 1979 impoundment. In
Opinaca reservoir, YCSI agrees with the proportion of small
specimens, suggesting a certain increase in recruitment after
impoundment. This is not borne out by CPUE values, which
decreased following impoundment. However, this decline
involved fish of all size classes and was too rapid to be
explained by reproductive failure. Results of complementary
samplings conducted in 1981 (Plante 1982) suggest that the
decrease in CPCTE, in this shallower reservoir, could be
due to walleyes avoiding the inshore sampling stations after
impoundment and occupying former beds of lakes and rivers
outside the zone of submerged trees.
The negative correlation observed between walleye CPUE
and water transparency and the positive correlation with temperature are due to the fish concentrating in the two less
transparent and warmer stations in La Grande 2 reservoir
and at the Boyd- Sakami station. The higher predation efficiency of walleyes in turbid water has frequently been mentioned in the literature (Vandenbyllaardt et al. 1991). On the
other hand, temperature may be a limiting factor at these
northern latitudes, the 54th parallel (northern part of
La Grande 2 reservoir) being the northern limit of distribution of walleyes in Quebec (Beauvais 1977, see footnote I).
Water temperature and spring warming rate have often been
mentioned as major determinants of walleye year-class
strength (Busch et al. 1975; Koonce et al. 1977; Forney
1980; Hokanson and Lien 1986).
Machniak (1975~)points out the importance of access to
good spawning sites and of substrate quality for this species'
reproductive success. Brouard (1983) and Gilles Shooner
Inc. (1984) showed that in La Grande 2 reservoir, some
walleye spawned on the slopes of a dike or on an old road
used to build it, or in tributaries. In Detcheverry Lake and
in Southern Indian Lake reservoir, walleyes also spawn in
tributaries (Gaudreault 1978; Bodaly 1980). Like the two
catostomids, walleyes should not lack good spawning sites in
the reservoirs of the La Grande complex. However, several
studies have shown a relationship between reservoir age and
the success of walleye populations (Jenkins 1970; Bennett
and McArthur 1990). In reservoirs where nearshore spawning grounds are selected, it takes 5 or more years before ice
and wave action loosens enough coarse material from the
shores for recruitment to improve (Machniak 1 9 7 5 ~ ) .
Lake trout
Several explanations for lake trout recruitment problems in
reservoirs have been suggested. Because of its homing
behavior, the species suffers a considerable disadvantage
during reservoir impounding because spawners show little
inclination to find new spawning sites in more suitable sectors (Gendron and Bklanger 1991). Moreover, winter drawdown probably limits the survival of embryos and alevins
because eggs are usually deposited in relatively shallow
water. Thus, lake trout reproduction has become impossible
in Bark Lake (Ontario) as a result of sizeable annual drawdowns of approximately 10 m (Wilton 1985). In Mitis reservoir (Quebec), the lake trout population has remained stable
in spite of mean winter drawdowns of 3 m (Gendron 1992).
The exceptional habitat available for the species and the scarcity of competitors are factors contributing to its success in
this reservoir. In Caniapiscau River, lake trout did not
experience recruitment problems following the river's cutoff, probably because the ancestral spawning grounds remained
accessible to spawners (Belzile 1990).
Secondary species
Because of the type of fishing gear used, it was impossible
to follow the dynamics of the small fish species in the
La Grande complex. However, diet studies of piscivorous
predators can give information on their abundance. For
example, Sage Ltke (1983) showed that sticklebacks represented the second most important group of prey, behind
coregonines, for walleyes in La Grande 2 and Opinaca reservoirs in 1981 and 1982; they also were the third most important prey of burbot in La Grande 2 reservoir. Recent studies
have also demonstrated the importance of sticklebacks in the
diet of ciscoes (R. Verdon, unpublished data).
Growth and condition
An increase in growth rate like that observed in La Grande 2
reservoir following impoundment has often been mentioned
for the northern pike and walleye, but less often for the
whitefish (Machniak, 1975a, 1975b, 1 9 7 5 ~ ) .In certain
reservoirs, the presence of competing planktivorous species,
coupled with a reduction in benthic resources after impoundment, led to decreased growth rates of young whitefish and
to a possible reduction in their rate of escape from predators
(Machniak 1 9 7 5 ~ ) .The general increase in primary and
secondary production after impoundment favors the recruitment of several fish species used as prey by northern pike
and walleyes, whose growth rates increase. The rise in fish
growth rates following impoundment is generally short-lived,
this parameter showing a decline with reservoir age (Nelson
1974).
The lesser improvement in the different species' condition
at the Boyd - Sakami station, compared with that observed in
the La Grande 2 and Opinaca reservoirs could be due to the
lower increase in overall productivity in this sector (DesLandes
1994). The colder thermal regime of Caniapiscau reservoir
could be responsible for the lesser improvement in condition
of the two catostomids, whereas the improvement for whitefish was comparable to that observed in the reservoirs in the
western sector. The improvement in lake trout condition in
Caniapiscau reservoir is worthy of mention.
Acknowledgments
We thank Martin Dufort and Roger Schetagne of HydroQuibec and Daniel Dussault of Groupe Environnement
Shooner Inc., who gave us access to the La Grande complex
environmental monitoring network data base. We are grate-
Can. J. Zool. Vol. 7 3 , 1995
ful to Hydro-Quebec's vice-presidence Environnement for
funding this study.
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