Nearshore Habitat Associations of Fish Assemblages in Waskesiu Lake, Saskatchewan
Date
1999
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Degree Level
Masters
Abstract
Knowledge of fish habitat associations in all types of lakes is important for
conservation and management to ensure that land developments or other human activities do
not have irreversible impacts on lake ecology. Sensitive fish species and aquatic habitats can
then be defined and considered in management decisions.
One purpose of this thesis was to define fish assemblages with relation to basic habitat
types of a typical boreal lake. Sensitive habitats and species were inferred from these fish
assemblage definitions. Another purpose was to determine whether boreal fish assemblages
are resilient to minor anthropogenic impacts, such as light fishing pressure or small water
control structures. Waskesiu Lake was chosen as a typical boreal lake because its fish
population structure is similar to other lakes in the mid-boreal region of Saskatchewan and
because its water quality and limnological characteristics are similar.
Assessments of the nearshore habitat and fish community of Waskesiu Lake were
conducted through field studies and literature reviews. Field studies included the examination
and description of habitat features of inshore areas of the lake. Fish communities of this
nearshore portion of the lake were examined during the two field seasons in summer 1994 and
1995.
These assessments indicated that there are diverse, patchily distributed habitats of
importance to a fish population composed of several distinct assemblages. Sandy substrate
areas were the dominant habitat types within the littoral zone, comprising 69.1% of that area
within the 2 m contour interval. These sandy areas supported a predominantly schooling fish
assemblage. The most commonly found fish species were juvenile white suckers, spottail
shiners, juvenile yellow perch, ninespine stickleback, and fathead minnows.
Sandy regions of Waskesiu Lake that were protected from strong wave action often
had dense aquatic macrophyte growth and also supported the greatest numbers of fish, both
benthivores and piscivores. These quiet areas contained fish assemblages that associated with
both emergent and submergent macrophytes. Strongest associations were found with
assemblages of brook stickleback, blacknose shiner, and northern pike. These weedy areas
are important for juvenile rearing of species such as northern pike and other species that rely
on aquatic macrophyte cover for feeding and protection, from predation.
Distinct fish assemblages were also found at rocky substrate locations, which cover
about 25% of the littoral zone floor. Consequently, fish species that associated with rocky
substrate were not a dominant component of the Waskesiu Lake fish community. These
species included slimy sculpin, longnose dace, and juvenile burbot. None of these species was
ever captured in substantial numbers during the littoral zone surveys. However, rocky
nearshore zones are also important for reproduction of other fish species, such as walleye,
cisco, lake whitefish, suckers, and trout-perch, as well as slimy sculpin and longnose dace.
Northern pike are the dominant (by number and biomass) predator in Waskesiu Lake's
littoral zone. They comprised the majority of piscivores in both 1994 and 1995. Walleye
were also a sizeable component of the nearshore piscivore community in 1994 but were
notably low in numbers in the littoral zone catch in 1995. They were a larger component of
the open-water catch in 1995 than northern pike. Walleye may have been foraging in off-
shore waters in 1995, in response to the distribution of their prey. However, lack of offshore
gill net data in 1994 precludes any solid conclusions regarding distributional changes.
A large variation in abundance was apparent for fish populations between years.
Substantially lower numbers of most fish species were captured in 1995. However, when
lower numbers of fish were captured in 1995, similar species-habitat associations were
apparent.
Population size variation was also apparent from the analyses of selected fish stomach
contents. Yellow perch were very abundant and the dominant forage of both pike and
walleye in 1994, although not the dominant small to medium body-size fish in either survey
year. White sucker and spottail shiner did not comprise substantial proportions of piscivore
diets in either year, although they were the most abundant potential forage fish in gear catches
in both survey years. This may have been a reflection of survey timing. Ninespine
sticklebacks were forage for not only walleye and northern pike in both survey years, but also
for yellow perch and cisco. The small relative body size (in comparison to perch) of ninespine
sticklebacks decreases their value as important forage for large fish but they would likely
supply valuable energy requirements for young northern pike, walleye, and for large yellow
perch.
Based on a literature review, changes in fish community composition, for both the
nearshore small fish species and for the off-shore large fish species, were not apparent from
early studies to this study. Given the diversity of habitat in Waskesiu Lake, and the built-in
resilience of most boreal fish species, little change in the fish community assemblages was
expected from pre-park years to the present. However, the apparent predominance of white
suckers in the 1994 and 1995 fish catches indicates that there may have been an effect on the
piscivorous populations from either recreational fishing pressure or emigration loss; or
perhaps a combination of the two.
Consequently, there have been no dramatic changes in Waskesiu Lake fish
populations over the past 70 years. Even rare taxa have not been impacted over time.
Species that may have been effected by minor perturbations, such as reductions in usage of
spawning streams (i.e., Kingsmere River, Mud Creek, and Waskesiu River), have likely been
able to compensate for losses by spawning in the lake or by adapting in some other way.
Consequently, the results of this study indicate that boreal fish assemblages in the general
region of Waskesiu Lake are resilient to minor perturbations. However, lakes in the region
should still be managed carefully and considered on a lake by lake basis.
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Degree
Master of Science (M.Sc.)
Department
Biology
Program
Biology