Food Web Interactions Among Walleye, Lake Whitefish, and Yellow Perch in Green Bay, Lake Michigan
File(s)
Date
2020-08Author
Koenig, Lucas
Publisher
College of Natural Resources, University of Wisconsin-Stevens Point
Advisor(s)
Isermann, Daniel
Metadata
Show full item recordAbstract
Green Bay supports important fisheries for walleye Sander vitreus, lake whitefish
Coregonus clupeaformis, and yellow perch Perca flavescens. While walleye and lake whitefish
populations have expanded in Green Bay, yellow perch numbers remain at historically low
levels. As one of the primary piscivores in the Green Bay food web, walleyes could influence
lake whitefish and yellow perch abundance, and yellow perch are important prey for walleye
within many ecosystems. Specifically, walleye and yellow perch populations in southern Green
Bay have exhibited contrasting trends in abundance since 1986. Walleye predation has been
hypothesized to represent a potential recruitment bottleneck for yellow perch in Green Bay,
which has been documented in other areas throughout the Great Lakes.
These three species likely interact in a variety of ways, including predation and diet
overlap, but these interactions are poorly understood because contemporary information on diets
is lacking. This information is needed to guide management decisions, because changes in
population status of one species will likely affect fisheries for the other two species. The specific
objectives of my research were to determine if: 1) lake whitefish and yellow perch represent
important prey for walleyes in Green Bay; 2) diets of these three species vary spatially and
temporally; 3) diet overlap among species is evident; and 4) the extent of walleye predation is
sufficiently high to influence recruitment potential of lake whitefish and yellow perch in the
portion of Green Bay south of Chambers Island (Zone 1).
Fish were collected each month from May through October in two zones of Green Bay
during 2018 and 2019 using monofilament graded mesh gill nets. Additional fish were collected
by natural resource agencies, commercial fishers, and recreational anglers. A total of 4,423
stomachs were dissected and diet items were removed and wet weighed to generate diet
compositions using diet information from 687 walleye, 533 lake whitefish, and 696 yellow perch
with nonempty stomachs. For each species, diet composition was described using mean
proportion by wet weight for each year, zone, and month combination. Analysis of similarities
(ANOSIM) was used to test for spatial and temporal differences in diet composition, Pianka’s
(1974) index of niche overlap was used to calculate the extent of diet overlap, and a combination
of bioenergetics and statistical catch-at-age (SCAA) modeling was used to estimate total walleye
consumption of lake whitefish and yellow perch from May 1 through October 31 during 2018.
Diet compositions suggest that lake whitefish and yellow perch comprise between 5-6%
of walleye diets overall, though temporal and spatial variation in diets was evident. Lake
whitefish were seasonally important prey consumed only during May and June in Zone 1,
comprising 36% of June walleye diets. Also, this study was the first to document the importance
of lake whitefish to walleye diets within the Great Lakes. In both zones, yellow perch
contributed to walleye diets at a broader temporal scale than lake whitefish, but perch never
comprised more than 15% of walleye diets in any month throughout Green Bay.
Walleye diet compositions were significantly different between zones, potentially
reflecting differences in prey fish availability. Additionally, significant temporal variation was
identified in Zone 1, with distinct seasonal transitions in the consumption of prey species.
Walleye diets were generally similar between 2018 and 2019, though fish collections during
2019 occurred at a reduced scale. Furthermore, variability in diet compositions was less evident
for lake whitefish and yellow perch. However, a significant difference was detected between
zones which was attributed to the greater contribution of round gobies Neogobius melanostomus
in lake whitefish and yellow perch diets identified in Zone 2. Similarly, a significant temporal
change in yellow perch diets was detected, largely attributed to increased consumption of round
gobies during the fall throughout Green Bay.
Diet overlap was strongest between lake whitefish and yellow perch, while weak to
moderate overlap was observed between walleye and both lake whitefish and yellow perch. The
highest degree of diet overlap between walleye and yellow perch occurred during October in
Zone 1, corresponding with increased contribution of gizzard shad Dorosoma cepedianum to the
diets of both species, and September in Zone 2, which was influenced most by predation on
round goby and yellow perch. Moreover, diet overlap was highly influenced by the invertebrate
prey group used in my diet analyses, as all invertebrate taxa were pooled. More specific
identification of invertebrate taxa in diets would likely increase the resolution and reliability of
my diet overlap indices, but this would be difficult because invertebrates were rarely intact in
many diets, especially for lake whitefish.
In conjunction with observed growth and monthly diet data, a range of abundance
estimates (i.e., 95% confidence limits) from SCAA models were used to predict the influence of
walleye predation on lake whitefish and yellow perch recruitment potential. Based on the range
of walleye consumption estimates and lake whitefish recruitment estimates, walleye
consumption appeared unlikely to influence recruitment potential of lake whitefish in Zone 1 of
Green Bay. However, given the high abundance of walleye and low abundance of yellow perch
estimated in Zone 1, yellow perch recruitment potential is likely affected by walleye predation.
These results corroborate other studies that have identified walleye predation as a
significant recruitment bottleneck for yellow perch populations throughout the Great Lakes. This
study also suggests that previous concerns related to walleyes negatively impacting lake
whitefish may be unrealistic. Additionally, alewife Alosa pseudoharengus, gizzard shad, and
invasive round gobies may serve as predation buffers for lake whitefish and yellow perch and
predation by my three focal species may help in regulating round goby abundance in Green Bay.
My results provide fisheries managers and stakeholders with important information regarding the
complex interactions among walleyes, lake whitefish, and yellow perch in Green Bay, so that
future management decisions can be made with a better understanding of the potential
implications for all three fisheries and prey resources.
Subject
Predation
Food web
Diet overlap
Consumption
Bioenergetics
ANOSIM
Recruitment potential