Diet Overlap and Food Habitats of Slimy Sculpin, Deepwater Sculpin, and Round Goby During Winter and Spring in Offshore Lake Michigan

Ecological stability in offshore benthic food webs of the Laurentian Great Lakes has been recently altered by non-native species such as round goby Neogobius melanostomus and quagga mussels Dreissena bugensis, as well as steep declines in biomass of Diporeia, a native amphipod. Correspondingly, population dynamics, life histories and the diet composition of native sculpins may be affected. I examined food habits of slimy sculpin Cottus cognatus, deepwater sculpin Myoxocephalus thompsonii, and round goby collected from January to May in 2009 and 2010 in Lake Michigan offshore of Frankfort (FF), MI; Muskegon (MSK), MI; Two Rivers (TR), WI; and Sturgeon Bay (STB), WI in depths of 69-128m. Important prey (by dry weight proportion and % occurrence) for slimy sculpin were Mysis (0.34, 45%), Diporeia (0.16, 34%), and Limnocalanus macrurus (0.22, 68%). Prey important to deepwater sculpin were Mysis (0.74, 92%) and Diporeia (0.16, 54%). Round goby consumed mainly bivalves (0.68, 95%) and Mysis (0.15, 37%). Diet composition for all three species did not vary across days sampled in January through April, and little variance was explained by year or depth sampled. Variance in diet composition for each benthivore species was best explained by the site from which fishes were sampled. For example, Diporeia constituted high diet proportions in sculpins offshore of TR and STB, but was absent in sculpins offshore of FF and MSK. Significant diet overlap (Schoener’s index ≥ 0.60) was identified between slimy and deepwater sculpin offshore of FF and STB but not offshore of TR. Significant diet overlap was not found between round goby and either sculpin species. Non-metric multi-dimensional scaling and cluster analyses revealed groups of fishes at each site with similar diets: 1) slimy sculpin only; 2) round goby only, and; 3) all deepwater sculpin, some slimy sculpin individuals, and very few round goby. Cluster analysis also distinguished groups for both sculpin species that reinforced the diet overlap results. Using genetic analyses on fish eggs taken from diet samples, bloater Coregonus hoyi and deepwater sculpin eggs were confirmed prey for slimy and deepwater sculpin in each month from February through May at all four sites sampled. Round goby consumed few deepwater sculpin eggs and no bloater eggs.Master of ScienceNatural Resources and EnvironmentUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/88164/1/londer absolute final.pd

Population‐level effects of egg predation on a native planktivore in a large freshwater lake

Using a 37‐year recruitment time series, we uncovered a field pattern revealing a strong, inverse relationship between bloater Coregonus hoyi recruitment success and slimy sculpin Cottus cognatus biomass in Lake Michigan (United States), one of the largest freshwater lakes of the world. Given that slimy sculpins (and deepwater sculpin Myoxocephalus thompsonii ) are known egg predators that spatiotemporally overlap with incubating bloater eggs, we used recently published data on sculpin diets and daily ration to model annual bloater egg consumption by sculpins for the 1973–2010 year‐classes. Although several strong year‐classes were produced in the late 1980s when the proportion of eggs consumed by slimy sculpins was extremely low (i.e., 0.10–1.0), egg predation failed to explain why recruitment was weak for the 1995–2005 year‐classes when the proportion consumed was also low (i.e., <0.02). We concluded that egg predation by slimy and deepwater sculpins could have limited bloater recruitment in some years, but that some undetermined factor was more important in many other years. Given that slimy sculpin densities are influenced by piscivorous lake trout Salvelinus namaycush , the restoration of which in Lake Michigan has lagged behind those in lakes Superior and Huron, our study highlights the importance of an ecosystem perspective when considering population dynamics of fishes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108675/1/eff12112.pd

Using Diets to Reveal Overlap and Egg Predation among Benthivorous Fishes in Lake Michigan

Ecological stability in the Laurentian Great Lakes has been altered by nonindigenous species, such as the Round Goby Neogobius melanostomus and dreissenid mussels, and by declines in native amphipods Diporeia spp. We evaluated whether these changes could influence diet overlap between three benthivorous fishes (Slimy Sculpin Cottus cognatus, Deepwater Sculpin Myoxocephalus thompsonii, and Round Goby) and whether predation on eggs of native species was occurring. We examined diets of fish collected at depths of 69â 128 m in Lake Michigan offshore of Frankfort and Muskegon, Michigan, and Two Rivers and Sturgeon Bay, Wisconsin, during Januaryâ May 2009 and 2010. Important prey (by dry weight proportion and by percent frequency of occurrence) for Slimy Sculpin were Mysis (0.34; 45%), Diporeia (0.16; 34%), and Limnocalanus macrurus (0.22; 68%); important prey for Deepwater Sculpin were Mysis (0.74; 92%) and Diporeia (0.16; 54%). Round Goby consumed mainly bivalves (i.e., dreissenids: 0.68; 95%) and Mysis (0.15; 37%). The two sculpin species consumed the eggs of Bloaters Coregonus hoyi (Slimy Sculpin: 0.04, 11%; Deepwater Sculpin: 0.02, 7%) and the eggs of Deepwater Sculpin (Slimy Sculpin: 0.03, 13%; Deepwater Sculpin: 0.05, 16%) during Februaryâ May at all sites. Round Goby also consumed eggs of these species but at lower levels (â ¤0.01; <1%). Diet overlap was identified between sculpin species at Frankfort and Sturgeon Bay, suggesting possible interspecific competition, but their diets did not overlap at Two Rivers; diet overlap was never observed between Round Goby and either sculpin species. Given that (1) diet overlap varied by site and (2) diet proportions varied spatially more than temporally, benthivores appear to be exhibiting localized responses to recent ecological changes. Overall, these results reveal that egg predation and interspecific competition could be important interactions to consider in future examinations of the population dynamics of these species or in ecosystem models that forecast how fisheries will respond to possible perturbations or management scenarios.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141248/1/tafs0492.pd

Evaluation of changes in Sculpin populations in the Great Lakes associated with shifts in benthic species composition

In the Great Lakes, slimy sculpins (Cottus cognatus) and deepwater sculpins (Myoxocephalus thompsonii) were historically abundant native deepwater fishes that served as important prey items for native piscivores (e.g., lake trout, Salvelinus namaycush, and burbot, Lota lota). However, both of these species have been declining in abundance and biomass recent decades according to USGS trawl surveys. The timing of these declines in sculpin biomass and abundance coincides with several ecological disturbances that have occurred throughout the Great Lakes, including the invasions of dreissenid mussels (zebra, Dreissena polymorpha; quagga, D. bugensis) and the aggressive round goby (Neogobius melanostomus), along with the collapse of Diporeia (formerly one of the most important prey items for these sculpin species). In this dissertation, we provide a comprehensive review of the state of knowledge and investigate the effect of these ecological disturbances on slimy and deepwater sculpins in the Great Lakes. We predicted that these ecological disturbances have negatively affected both slimy and deepwater sculpin populations, particularly slimy sculpins, which we could observe through changes in their spatial (depth) distribution patterns (e.g., shifting deeper to avoid round goby) and body condition (e.g., lower body condition associated with ecological disturbance). Our results indicate that slimy sculpins may be more vulnerable to these ecological disturbances than deepwater sculpins, but data limitations prevent us from offering conclusive causal mechanisms for sculpin spatial and body condition patterns. Both our review and analyses implicate that we need to gain a better understanding of sculpins in order to restore these species in this system.Thesis (M.S.)--Michigan State University. Fisheries and Wildlife, 2019Includes bibliographical reference

Diel interactions between prey behaviour and feeding in an invasive fish, the round goby, in a North American river

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72558/1/j.1365-2427.2006.01527.x.pd

TROPHIC DYNAMICS OF THE LAKE SUPERIOR FISH COMMUNITY

The Lake Superior food web has undergone many changes in recent decades, including the rehabilitation of the native apex predator lake charr (Salvelinus namaycush) and the introduction of several nonnative species. The trophic linkages and ecological requirements of the entire fish community, including predators and prey fishes, has not been assessed on a whole-lake scale in over a decade. Here, I investigated the trophic dynamics across multiple regions of the lake, and estimated the consumptive effect of lean lake charr in one region of Lake Superior. From April to October of 2021, a total of five predator, four large prey fish, and five small prey fish species were collected by region and length class during coordinated, standard gillnet and bottom-trawl surveys. To assess trophic linkages, gut contents were examined and biomass, count, and length were measured. Additionally, twelve common lean lake charr diet items were collected during summer 2022, analyzed for energy density, and used to estimate a population-level consumption of leans. I found a high degree of interconnectedness in the Lake Superior food web, with Mysis as a keystone diet item for the entire fish community. Lake Superior predators displayed regional variance, ontogenetic shifts in diet structure, and opportunistic feeding strategies. Conversely, prey fish diets were less diverse, primarily reliant on Mysis and Diporeia, and were more likely to have a single dominant diet item. This study improves our understanding of Lake Superior trophic dynamics and provides a baseline for future food web and bioenergetics modeling in the lake

Influence of Diporeia Density on Diet Composition, Relative Abundance, and Energy Density of Planktivorous Fishes in Southeast Lake Michigan

The benthic amphipod Diporeia spp. is an important prey for many fish in offshore areas of the Great Lakes, but its abundance has been rapidly decreasing. To assess the influence of Diporeia availability on the food habits, relative abundance, and energetics of planktivorous fish, the diet composition, catch per unit effort (CPUE), and energy density of plantkivorous fish in southeast Lake Michigan during 2000–2001 were compared among locations with different Diporeia densities. Diporeia densities at St. Joseph, Michigan, were near 0/m2 over much of the bottom but averaged more than 3,800/m2 at Muskegon and Little Sable Point, Michigan. Consistent with these differences in Diporeia density, fish diet composition, CPUE, and energy density varied spatially. For example, alternative prey types comprised a larger fraction of the diets of bloater Coregonus hoyi, large (>100 mm total length) alewife Alosa pseudoharengus, and slimy sculpin Cottus cognatus at St. Joseph than at Muskegon and Little Sable Point. This pattern was seasonally dependent for alewives and bloaters because Diporeia were eaten mainly in June. Food biomass per stomach was not lower at St. Joseph than elsewhere, suggesting that the spatial variation in diet composition was due to greater consumption of alternative prey by fish at St. Joseph. Although slimy sculpin and bloaters were able to feed on alternative prey, the CPUE of these species at certain depths was considerably lower at St. Joseph than at Muskegon or Little Sable Point, indicating that Diporeia availability may also influence fish abundance and distribution. Finally, a link between Diporeia density and fish energetics was suggested by the comparatively low energy density of deepwater sculpin Myoxocephalus thompsonii and large alewives at St. Joseph, a result that may reflect the low energy content of other prey relative to Diporeia.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141042/1/tafs0588.pd

Long-Term Impacts of the Invasive Round Goby Neogobius melanostomus on Fish Community Diversity and Diets in the St. Clair River, Michigan

Round gobies (Neogobius melanostomus) were first documented within the St. Clair River in 1990, and subsequently impacted native benthic fishes, including sculpins and darters, through direct predation and competition for space and prey. In order to identify long-term impacts on fish species associated with the round goby invasion in the St. Clair River, Michigan, I compared fish community composition and diet overlap between round goby and native species in 1994 with similar data from 2011. All fish were collected by trawls (3-, 5-, 7-, 9-, 11-m depths) and seines (1 m) in May, July, and September 2011, and compared to similar data collected in May, June, and September 1994. Catch-per-unit effort (CPUE) for rainbow darter (Etheostoma caeruleum) and round goby significantly decreased in the nearshore zone between 1994 and 2011. In the offshore zone, relative abundance of northern madtom (Noturus stigmosus) decreased significantly between 1994 and 2011, while round goby relative abundance both increased and decreased, depending on month. CPUE of channel darter (Percina copelandi), johnny darter (Etheostoma nigrum), mottled sculpin (Cottus bardii), and round goby also significantly decreased in the offshore zone between 1994 and 2011. There was significant diet overlap between round gobies and native rainbow darter in 1994, suggesting diet overlap and competition for food contributed to rainbow darter population declines in the St. Clair River from 1994 to 2011. However, significant diet overlap was also found in both years between round goby and other native species that did not decline from 1994 to 2011. In 2011, round gobies showed significant diet overlap with rock bass (Ambloplites rupestris) in the nearshore zone, and significant overlap with logperch (Percina caprodes) and trout-perch (Percopsis omiscomaycus) in the offshore zone. In 1994, reliance on zebra mussels (Dreissena polymorpha) by adult round goby prevented frequent significant diet overlap from occurring between large round gobies and native species that could not consume zebra mussels, but in 2011, round gobies, logperch, and trout-perch all consumed quagga mussels (Dreissena bugensis). These results suggest that differential foraging strategies allowed some native fish to forage without competition from round goby, and that the negative impacts of the round goby invasion and establishment on fish species diversity within the St. Clair River may be isolated to a few species, and due to competition for other resources, such as space. Establishment of the round goby within Great Lakes tributaries, nearshore environments, and more recently the Mississippi River basin will likely have differing impacts on native fish communities based on the pre-existing communities, other environmental stressors, and foraging habits of native fishes.Master of ScienceNatural Resources and EnvironmentUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/102013/1/Erin Burkett Thesis FA13.pd