Identifying important micro-habitat characteristics of muskellunge spawning locations in the upper Niagara River

Conserving and restoring muskellunge (Esox masquinongy) spawning habitat are essential for maintaining self-sustaining populations. A Maxent model was developed based on presence and background data to investigate the relationship between the occurrence of spawning muskellunge and habitat features in the upper Niagara River. Muskellunge spawning points (n = 15) were determined by direct observation of spawning pairs. Model inputs were based on micro-habitat features collected at each spawning point and a sample of 250 background habitat points. The full model was reduced to a four variable model to remove uninformative variables and reduce overfitting and redundancy. Model performance was evaluated based on the mean test gain of cross-validated models (n = 15). Model outputs identified aquatic macrophyte/algae coverage as the most important habitat feature at spawning locations. The relative probability of muskellunge spawning increased with the percent rank of total aquatic macrophyte/algae coverage, water velocity, and water depth and it was highest at points with muddy-sand to sand substrates. Mean test gain (0.68; SE = 0.52) of the cross-validated models indicated that the likelihood of an average muskellunge spawning point was nearly two times greater than an average background point. Results from this research advance our knowledge of muskellunge reproductive ecology, while providing scientists and managers with quantitative measures to guide habitat conservation and restoration.     

Round Goby and Mottled Sculpin Predation on Lake Trout Eggs and Fry: Field Predictions from Laboratory Experiments

The accidental introduction of round gobies (Neogobius melanostomus) into the North American Great Lakes has raised concerns about their potential impacts on local fauna. Gobies have similar habitat and spawning requirements to mottled sculpins (Cottus bairdi) and slimy sculpins (C. cognatus), and may already be displacing sculpins where the ranges of the species overlap. Like sculpins, gobies are capable of penetrating interstitial spaces to acquire food, and therefore may become predators of interstitially incubating lake trout eggs. Laboratory experiments were conducted to compare egg consumption rates and critical size (the minimum size at which a fish was capable of ingesting an egg) between round gobies and mottled sculpins. Predation by both species on lake trout eggs and fry was also examined in two grades of substrate (cobble and gravel). Mottled sculpins consumed larger numbers of eggs than round gobies of similar size, and were capable of ingesting eggs at smaller sizes than gobies. Both gobies and sculpins had lower foraging success on smaller substrates (gravel) than on cobble. Gobies are currently present at higher densities than sculpins in areas where they are established in the Great Lakes. The similar predation of lake trout eggs by round gobies and mottled sculpin and high densities the goby has achieved at some Great Lakes sites leads to the prediction that the round goby may negatively affect lake trout reproduction and therefore rehabilitation.     

Round goby (Neogobius melanostomus) and native fishes as potential nest predators of centrarchid species in the upper St. Lawrence River

Widespread invasion of Round Goby (Neogobius melanostomus) throughout the Great Lakes has raised concerns regarding increased egg predation on fish species. To better understand nest predation, we examined nesting habitat selected by three upper St. Lawrence River Centrarchid species and the predator assemblage at nests during the 2011 and 2012 egg incubation and larval periods. Following removal of guarding males by angling, 5-min observations were used to identify and enumerate predators at rock bass (Ambloplites rupestris; n = 81), pumpkinseed (Lepomis gibbosus; n = 80), and smallmouth bass (Micropterus dolomieu; n = 40) nests. Differences in nesting habitat among centrarchids corresponded with differences in nest predator assemblages along a gradient defined primarily by depth and substrate. Pumpkinseed nests in shallow depths with soft substrate were visited principally by minnow spp., but few round goby. Smallmouth bass nests at greater depth with hard substrates were frequented nearly exclusively by round goby, while rock bass nests at intermediate depth with a mix of hard and soft substrates were visited by round goby and yellow perch (Perca flavescens). Rock bass nests had a higher predator burden than pumpkinseed nests in 2011, but no differences were observed among centrarchid species in 2012. Round goby were a major component of the predators at rock bass and smallmouth bass nests. However, predation burden imposed by yellow perch was higher than round goby at rock bass nests. We conclude nesting habitat selection influences native and non-native egg predator assemblages, but whether round goby predation is additive or compensatory remains unclear.     

Predation on Lake Trout Eggs and Fry: a Modeling Approach

A general model was developed to examine the effects of multiple predators on survival of eggs and fry of lake trout, Salvelinus namaycush, associated with spawning reefs. Three kinds of predation were simulated: epibenthic egg predators consuming eggs on the substrate surface during spawning, interstitial egg predators that can move in rocky substrate and consume incubating eggs, and fry predators. Also simulated was the effect of water temperature on predation rates. The model predicted that interstitial predation on eggs accounted for most (76 to 81%) of the predation on early life history stages of lake trout; epibenthic egg predation (12 to 19%) and fry predation (0 to 12%) had less effect on lake trout survival. Initial predation conditions chosen for the model were: epibenthic egg predation peaked at 2 eggs/m²/d over 30 d, interstitial egg predation at 2 eggs/m²/d over 180 d, and fry predation at 1 fry/m²/d over 60 d. With a starting egg density of 100 eggs/m² and initial predation conditions, no lake trout were estimated to survive to swim-up. At egg densities of 250 eggs/m², 36% of the lake trout survived. At the highest egg densities examined, 500 to 1,000 eggs/m², estimated survival increased to about 70 to 80%. Simulated survival rates of lake trout decreased dramatically as predation rate increased but were not as sensitive to increases in the duration of predation.     

Prey selection and time to consumption differ between congeneric muskellunge and northern pike

Understanding whether fishes feed selectively is important for informing conservation and management actions such as selecting receiving waters for stocked fishes and prioritizing nursery habitats for preservation or restoration. We conducted a laboratory experiment to determine if (1) age-0 muskellunge (Esox masquinongy) and northern pike (E. lucius), two primarily piscivorous congeners in the Laurentian Great Lakes, fed selectively among four prey species (bluntnose minnow [Pimephales notatus], johnny darter [Etheostoma nigrum], rock bass [Ambloplites rupestris], and yellow perch [Perca flavescens]) with different anti-predator behaviors and morphologies, and (2) prey selection and time to consumption differed between predators. Muskellunge strongly selected bluntnose minnow and avoided the other prey species. Northern pike also strongly selected bluntnose minnow and avoided johnny darter and rock bass, but exhibited slight avoidance to neutral selection of yellow perch. Mean time to consumption differed between species, with northern pike feeding more quickly than muskellunge. Further controlled experimentation is needed to reveal whether growth and survival differs when these predators consume preferred vs. non-preferred prey. In the interim, we recommend managers presume nursery habitats with soft-rayed, fusiform, non-demersal prey fishes are most likely to support growth and survival of age-0 muskellunge and northern pike.     

Predation on Walleye Eggs by Fish on Reefs in Western Lake Erie

We examined diets of fishes from gillnet and egg pump collections conducted on reefs in western Lake Erie during walleye (Sander vitreus) egg incubation periods from 1994–1999 and 2004 to assess incidence of walleye eggs in fish diets. We collected no potential egg predators in samples taken in 1994 but from 1995–1999 and in 2004 we caught 22 different species of fish on reefs in addition to spawning walleye. In most years, white perch (Morone americana) stomachs contained more walleye eggs than any other species on the reefs averaging 253 eggs per stomach. We also found lower numbers of walleye eggs in the stomachs of channel catfish (Ictalurus punctatus; 53 eggs/stomach), johnny darter (Etheostoma nigrum; 2 eggs/stomach), logperch (Percina caprodes; 10 eggs/stomach), quillback (Carpiodes cyprinus; 184 eggs/stomach), rock bass (Ambloplites rupestris; 3 eggs/stomach), round goby (Neogobius melanostomus; 4 eggs/stomach), sculpin (Cottidae; 21 eggs/stomach), silver chub (Macrhybopsis storeriana; 3 eggs/stomach), spottail shiner (Notropis hudsonius; 14 eggs/stomach), trout-perch (Percopsis omiscomaycus; 30 eggs/stomach), white sucker (Catastomus commersonii; 20 eggs/stomach), and yellow perch (Perca flavescens; 181 eggs/stomach). Similar to other studies of predation on walleye eggs, our results indicate that prolonged incubation periods increase the potential for egg loss due to predation.     

Do native predators feed on non-native prey? The case of round goby in a fluvial piscivorous fish assemblage

We evaluated whether or not the invasive round goby (Neogobius melanostomus) represents an important prey source for seven native fish predators in Lake St. Pierre (St. Lawrence River, Canada). The frequency of occurrence of round goby in the stomach contents of brown bullhead (Ameiurus nebulosus) and channel catfish (Ictalurus punctatus) was very low (< 5%), while for the five other predators, it varied between 22% (yellow perch; Perca flavescens) and 65% (sauger; Sander canadensis). Several competing models linking the probability of occurrence of round goby in stomach contents to variables related to space, physical habitat, biotic interactions and predator size were tested for the five species feeding on round goby. Results indicated that space variables influenced round goby occurrence in stomachs for all species. In addition, physical habitat variables had an influence for sauger and walleye (Sander vitreus); biotic variables had an influence for yellow perch, walleye and sauger; and size had an influence for northern pike (Esox lucius), smallmouth bass (Micropterus dolomieu) and walleye. These results are discussed in light of known biological features of the round goby and native predators studied here and have important implications in terms of understanding round goby invasion success in the Great Lakes–St. Lawrence system.     

Thirty-year update: Changes in biological characteristics of degraded muskellunge nursery habitat in southern Georgian Bay,Lake Huron,Canada

Aquatic vegetation is a critical component of nursery habitat for young-of-the-year (YOY) muskellunge. The trophy status of the muskellunge fishery in southeastern Georgian Bay owes its reputation to the widespread distribution of aquatic vegetation in coastal marshes of this region. Unfortunately, wetland habitat has been in decline because of an unprecedented period of sustained low water levels since 1999. In this study, we strategically re-sampled 16 historic sites that supported YOY muskellunge in 1981. The sustained low water levels and increased shoreline modifications experienced by southeastern Georgian Bay may have contributed to the current disappearance of YOY muskellunge at those sites. These physical stressors appeared to have altered the habitat structure of the plant community and led to changes in fish communities, making them no longer suitable for YOY muskellunge. The precise mechanisms limiting survival to the YOY stage are unknown because spawning adults have been observed in the area in the spring of 2012 and 2013. These results corroborated previous sampling programs at the historic sites (2004–2005: n = 8 and 2007: n = 16) that employed other fishing gears and protocols as well as a supplemental YOY sampling in 2013 (n = 26 additional sites). If this muskellunge population is to remain self-sustaining, a complementary management strategy specifically developed for Georgian Bay is required. The strategy should identify and ultimately protect suitable muskellunge breeding habitat by accounting for the unique geomorphology, current physical stressors affecting Georgian Bay, and the biological links between suitable spawning and nursery habitats.     

Round goby (Neogobius melanostomus) population structure,biomass, prey consumption and mortality from predation in the Bay of Quinte,Lake Ontario

We compared round goby (Neogobius melanostomus) population structure and biomass, estimated the quantity of prey consumed by round goby and assessed predation on round goby in two areas of the Bay of Quinte (upper and lower bay) that were invaded by this species two years apart. A bioenergetics approach was used to estimate round goby consumption and to illustrate the influence of changes in the round goby biomass, from May to October in both areas of the bay. Mean round goby biomass was 5 tonnes/km² for the upper bay and 11.2 tonnes/km² for the lower bay. Round goby populations were dominated by age-0 to age-2 individuals; older individuals were rare although they constituted a greater portion of total biomass in the earlier invaded lower bay than the upper bay. Estimated round goby consumption was 78.4 tonnes/km² for the upper bay and 127.1 tonnes/km² for the lower bay; dreissenids were the most important prey followed by chironomids, zooplankton and amphipods. Diet analysis showed that round gobies were consumed by all predator species analyzed, and constituted a high percentage of stomach content biomass in yellow perch (Perca flavescens), largemouth bass (Micropterus salmoides) and northern pike (Esox lucius). Age structure differences between the upper and lower bay are consistent with those expected between expanding and stable populations.     

An evaluation of fish spawning on degraded and remnant reefs in Saginaw Bay,Lake Huron

Saginaw Bay is a shallow, nutrient-rich embayment in Lake Huron that historically had a complex network of natural rocky reefs. These reef habitats were used as spawning and nursery areas for a variety of fish species, but decades of land-use related sedimentation caused many of these reefs to be degraded. Our study objectives were to analyze abiotic and biotic conditions on degraded and remnant reefs and describe spawning patterns of walleye (Sander vitreus) and lake whitefish (Coregonus clupeaformis) at these sites to determine the potential for increased utilization following reef restoration. During fall and spring 2014–2016, we evaluated water quality and egg predation at four sites with varying levels of reef degradation. Further, we documented reproductive utilization through capture of spawning adults and quantification of egg deposition. Walleye and lake whitefish utilized multiple sites for reproduction; however, densities of spawners and deposited eggs were low, suggesting that they were not utilizing study sites as major spawning locations. Walleye and lake whitefish eggs were eaten by multiple fish species, including larger fish such as channel catfish (Ictalurus punctatus). Dissolved oxygen levels were adequate (i.e., >7 mg 0₂ L^?1) during spring walleye egg incubation; however, bottom dissolved oxygen levels became very low at some sites during winter ice cover, coinciding with lake whitefish egg incubation. As restoration of rocky reefs proceeds in the Bay, evidence of remnant reef spawning fish bodes well for long-term success, though potential limiting factors such as low dissolved oxygen, sedimentation, and egg predation require continued monitoring.     

Predation on Lake Whitefish Eggs by Longnose Suckers

In November 1981, we observed intense predation on lake whitefish (Coregonus clupeaformis) eggs by longnose suckers (Catostomus catostomus) on lake whitefish spawning grounds in northwestern Lake Huron. Since longnose suckers commonly frequent the same habitat used by spawning lake whitefish, there exists the potential for high losses of eggs due to sucker predation.     

Density,production, and survival of walleye (Sander vitreus) eggs in the Muskegon River,Michigan

Walleye (Sander vitreus) is an important sport fish in the Great Lakes that is experiencing low reproductive success after severe population declines starting in the late 1940s. In the Muskegon River, Michigan, natural reproduction of walleyes remains low and is largely supplemented by stocking. To determine factors influencing walleye reproductive success in the Muskegon River, we estimated walleye egg survival using insitu egg incubators covered with nitex screening (2003–2004) and estimated density and survival of fertilized eggs caught on furnace filter traps across different substrate types (2005–2006). We compared physical habitat suitability for walleye eggs under high and low flow scenarios. Density of walleye eggs was highest in regions of gravel/cobble substrates. Egg survival was higher in egg incubators (24–49.5%) than on furnace filter traps (2.0%), suggesting predation is an important source of walleye egg mortality in the Muskegon River. Cold water temperatures that extended developmental stage durations may also be an important source of egg mortality. The dynamic habitat suitability model predicted low suitability for eggs due to poor temperature and velocity conditions. Despite low egg survival rates, 40 million to 1 billion eggs were estimated to hatch. The low natural reproduction of walleyes in the Muskegon River is likely due to a combination of low walleye egg survival and failure of walleye larvae to reach their nursery grounds in Muskegon Lake.     

Lake Trout Spawning on Artificial Reefs and the Effect of Zebra Mussels: Fatal Attraction?

Lake trout stocked in the Great Lakes appear to spawn primarily on shallow reefs (< 16 m deep), particularly on breakwaters or water intake lines. Shallow water substrates are being rapidly colonized by zebra mussels, potentially resulting in degraded substrate and interstitial water quality. The attraction of spawning lake trout to new substrate and the effect of zebra mussels on spawning success was examined. Lake trout eggs and fry were collected on clean cobble and cobble fouled with zebra mussels at the Port of Indiana in southern Lake Michigan, and on each of three recently constructed submerged reefs. Egg deposition was similar among all sites except on new, unfouled cobble, where deposition was 11 to 29 times higher, depending on the collection device used. The ratio of empty egg chorions to intact eggs was similar among all sites except the fouled substrate, where the ratio was 129× higher (P < 0.001). Fry catches were similar on fouled and unfouled substrate, but 6.5 × higher on one of the new reefs (P < 0.01). In laboratory incubators, egg hatching rates were similar in cobble with and without zebra mussels. Lake trout were attracted to spawn on newly constructed artificial reefs, but the presence of zebra mussels appeared to reduce egg deposition and increase damage to eggs. Artificial reefs may successfully increase the amount of spawning substrate available for lake trout, but if they are constructed in shallow water they may not be productive areas for egg incubation and fry hatch due to the presence of zebra mussels, shallow-water egg and fry predators, and storm surge.     

Relationship between lake trout spawning,embryonic survival,and currents: A case of bet hedging in the face of environmental stochasticity?

Lake trout, Salvelinus namaycush, spawning in the Great Lakes occurs primarily on cobble substrate at relatively shallow water depths that can experience strong water currents. Strong currents may limit embryonic survival by damaging or displacing eggs, but may also reduce the accumulation of fine material and limit foraging by potential egg predators. To better understand the importance of currents, we evaluated the role of currents in spawning habitat selection, egg density and survival, and egg predator density at a spawning reef in Lake Champlain (USA). Most spawning occurred one week after the largest storm event associated with the strongest currents and greatest upwelling. Highest spawning activity was associated with a relatively shallow part of the reef that had the highest current velocity and greatest potential for egg displacement. Within the interstices, the survival of naturally deposited eggs was unrelated to the concurrent loss of artificial eggs. We propose that the reproductive strategy of spawning on shallow areas of a reef that have the highest current velocity and high potential for egg loss represents a type of bet hedging to optimize survival of those embryos that remain within interstices. This strategy may have evolved in response to environmental stochasticity that resulted in higher egg survival.     

The effect of discharge and predation on habitat use by wild and hatchery brown trout (Salmo Trutta)

The effects of trout stock, discharge and predation risk on habitat use by brown trout, Salmo trutta, were studied in four artificial streams. Trout stock had no effect on habitat use as both wild and hatchery fish used similar habitats. The presence of pike (Esox lucius) caused trout to decrease their use of pools, the habitat in which pike occurred, and increase their use of other habitats. Decreasing discharge reduced available area of the stream and resulted in fewer fish in the shallow margins. Both decreased flow and increased predation risk caused more overlap in habitat use, and thus increased the potential for intraspecific competition, predation and the use of poorer habitats. The results illustrate the danger of applying habitat use relationships obtained from one stream to all other streams where habitat availability and biotic interactions may differ.     

The influence of light,substrate, and fish on the habitat preferences of the invasive bloody red shrimp,Hemimysis anomala

The invasive bloody red shrimp, Hemimysis anomala, is a novel organism in the Laurentian Great Lakes region that utilizes benthic and open-water habitat. Hemimysis is predicted to impact nearshore fish communities in the Northeastern USA where its range is expanding, either negatively through predation of shared zooplankton prey or positively as high-calorie prey. In this experimental study, we examined the factors influencing Hemimysis’ benthic habitat selection, vertical distribution, and susceptibility to fish predation. In the presence of fish cues, Hemimysis preferred cobble over other benthic substrates (Dreissena mussels, pebble, or sand) regardless of light conditions; in dark conditions without a fish present, Hemimysis preferred open waters with sand habitat. Light and fish cues also interacted to influence the vertical distribution of Hemimysis, with the majority of mysids selecting depths that minimized perceived cumulative risk. The mean feeding rates of young-of-year (YOY) alewife (Alosa pseudoharengus), adult round goby (Neogobius melanostomus), YOY yellow perch (Perca flavescens), adult pumpkinseed sunfish (Lepomis gibbosus), and YOY lake trout (Salvelinus namaycush) varied among species, prey densities, and substrate (range = 0.77–57 mysids/fish/h). In general, feeding rates were highest for alewife, a non-native species in the Great Lakes basin, and in refuge-free conditions for all species, except for non-native round goby, which fed at similar rates regardless of prey refuge availability. Collectively, our results suggest that fish feeding success is contingent upon the interaction of light and Hemimysis refuge availability due to behavioral modifications of Hemimysis in the presence of fish and adverse light conditions.     

Density and habitat use by the round goby (Apollonia melanostoma) in the Bay of Quinte,Lake Ontario

We assessed round goby (Apollonia melanostoma) density and size structure in two sections of the Bay of Quinte (Lake Ontario) that had been invaded by this species two years apart. Round goby density was assessed with 50 m linear transects, recorded with an underwater video recording apparatus developed for this study that included a depth sounder for maintaining a fixed distance above the substrate. The highest mean round goby densities were observed in the shallowest depth zone (1.5–3 m) at both sites, but there were differences between the sites in the habitat types where the highest densities occurred and there were no significant density differences among habitat types at either site (rock with sparse vegetation, mud with sparse vegetation, sand/mud with moderate vegetation cover). In the upper bay, mean body length of round gobies declined with depth, whereas in the lower bay, mean round goby length was greatest in the deepest zone. Mean body length of round gobies did not differ significantly by habitat type in either section of the bay.     

Behavioural interactions between prey (trout smolts) and predators (pike and pikeperch) in an impounded river

Movements of radio‐tagged pike Esox lucius (L.), pikeperch Stizostedion lucioperca (L.) and outward migrating sea trout smolts Salmo trutta (L.) were studied in a shallow Danish reservoir to obtain information of predator–prey interactions between these species. Twenty pikeperch (55–74 cm) and 19 pike (52–72 cm) were tagged. Female pikeperch spent more time near the outlet sluice during the smolt run (May) than at other times of the year, apparently actively hunting the smolts delayed in this area. In contrast, male pikeperch did not seem to participate in the smolt predation but remained stationary during the smolt run, presumably guarding their nests. Most tagged pike were present at the spawning grounds during the peak of the smolt run, where they had little chance of smolt encounter. Twenty migrating trout smolts were radio‐tagged in the river upstream of the reservoir. Ten of these were located in the vicinity of the outlet sluice at least once, but were unwilling or unable to find and enter the sub‐surface outlet sluice. Only one tagged smolt left the reservoir. After 1–12 days in the reservoir, the remaining smolts were eaten by pikeperch or pike and the results indicate that female pikeperch and few female pike have adjusted their behaviour to predation on smolts during the smolt run. The smolt predation in this man‐made reservoir is higher than in natural lakes, probably due to the changed physical environment and introduced predators, such as pikeperch. The outlet sluice practice and the temporal overlap between smolt run and predator‐spawning may be key factors in smolt survival. Copyright © 2000 John Wiley & Sons, Ltd.     

Slimy sculpin depth shifts and habitat squeeze following the round goby invasion in the Laurentian Great Lakes

The collapse of Diporeia spp. and invasions of dreissenid mussels (zebra, Dreissena polymorpha; quagga, D. bugensis) and round goby (Neogobius melanostomus) have been associated with declines in abundance of native benthic fishes in the Great Lakes, including historically abundant slimy sculpin (Cottus cognatus). We hypothesized that as round goby colonized deeper habitat, slimy sculpin avoided habitat competition, predation, and aggression from round goby by shifting to deeper habitat. Accordingly, we predicted increased depth overlap of slimy sculpin with both round goby and deepwater sculpin (Myoxocephalus thompsonii) that resulted in habitat squeeze by both species. We used long-term bottom trawl data from Lakes Michigan, Huron, and Ontario to evaluate shifts in slimy sculpin depth and their depth overlap with round goby and deepwater sculpin. Lake Huron most supported our hypotheses as slimy sculpin shifted to deeper habitat coincident with the round goby invasion, and depth overlap between slimy sculpin and both species recently increased. Slimy sculpin depth trends in Lakes Michigan and Ontario suggest other ecological and environmental factors better predicted sculpin depth in these lakes.