Smallmouth Bass Research Articles

Is Bigger Better? Evaluation of Size‐Selective Predation on Age‐0 Walleye

AbstractThe success of fish stocking programs is dependent on poststocking survival. However, survival can be influenced by size‐selective mortality, where larger individuals are expected to be less vulnerable to predation. Walleye Sander vitreus is a commonly stocked sport fish, but little is known regarding the role of size‐selective predation on age‐0 Walleye (90–290 mm TL) that are stocked in the presence of various piscivores with different foraging strategies and morphological features. Our objective was to evaluate whether the TL of consumed age‐0 Walleye was related to predator TL, predator gape height, or the probability of predation. We also assessed whether length distributions varied among stocked, recaptured, and consumed age‐0 Walleye. Data for the food habits of Largemouth Bass Micropterus salmoides, Smallmouth Bass M. dolomieu, Northern Pike Esox lucius, adult Walleye, and Muskellunge Esox masquinongy were collected from East Okoboji Lake and West Okoboji Lake, Iowa, USA during fall 2015–2017. Over the course of the study, 301 age‐0 Walleye were recovered from 3,514 predator stomachs. Mean, maximum (85th percentile), and minimum (15th percentile) TL of the consumed age‐0 Walleye were not related to the TL or gape height of the predators (P > 0.05), but the probability of predation decreased by 0.02 for every 10‐mm increase in the TL of the age‐0 Walleye. The length distributions indicated that consumed Walleye were generally smaller, whereas recaptured Walleye tended to be larger than stocked fish were. Our approach to evaluating poststocking size‐selective predation on age‐0 Walleye furthers the current understanding of the importance of size at stocking relative to stocking success and suggests that stocking Walleye > 220 mm is economically advantageous for reducing predation risk.

Draft Genome Sequence of an Adomavirus Associated with Raised Mucoid Skin Lesions on Smallmouth Bass (Micropterus dolomieu).

Raised mucoid skin lesions have been observed on smallmouth bass (Micropterus dolomieu) for years. Here, we report the draft genome of a novel adomavirus (Micropterus dolomieu adomavirus 2) associated with this disease. The circular genome is 17,561 bp and most similar to that of alpha-adomaviruses.

Going the Distance: Influence of Distance Between Boat Noise and Nest Site on the Behavior of Paternal Smallmouth Bass

The effects of anthropogenic noise have garnered significant attention in marine ecosystems, but comparatively less is known about its impacts on freshwater ecosystems. For fish that provide parental care, the effects of acoustic disturbance could have fitness-level consequences if nest tending behavior is altered. This study explored the effects of motorboat noise on the parental behavior of nesting male smallmouth bass (Micropterus dolomieu; Lacepede, 1802), an important freshwater game fish in North America that provides sole paternal care to offspring. Specifically, we evaluated how boat noise proximity to a bass nest (ranging from 4.5 to 90 m) influenced paternal care behaviors. A total of 73 fish were exposed to a 3-min motorboat playback designed to simulate a boat sound that typically occurs in areas near littoral nesting sites. The fish were video recorded, and their behaviors were analyzed before, during, and after exposure to the playback. Residency time was the only behavioral metric to be adversely affected by noise playbacks but only when in close proximity to the speaker. Our results suggest that boat noise may have an impact on bass reproductive fitness in specific contexts where combustion motors are used near shore during the nesting period. The largely null findings may indicate a resilience to boat noise and/or habituation to the noise. In addition, boats displace water and create waves that represent another form of disturbance that could be experienced by fish but was not simulated here. Future research should integrate behavioral and physiological responses to boat noise and other aspects of boat disturbance to better understand the fitness impacts of boating activity on freshwater fish.

Reconnaissance of Surface Water Estrogenicity and the Prevalence of Intersex in Smallmouth Bass (Micropterus Dolomieu) Inhabiting New Jersey

The observation of testicular oocytes in male fishes has been utilized as a biomarker of estrogenic endocrine disruption. A reconnaissance project led in the Northeastern United States (US) during the period of 2008–2010 identified a high prevalence of intersex smallmouth bass on or near US Fish & Wildlife Service National Wildlife Refuges that included the observation of 100% prevalence in smallmouth bass males collected from the Wallkill River, NJ, USA. To better assess the prevalence of intersex smallmouth bass across the state of New Jersey, a tiered reconnaissance approach was initiated during the fall of 2016. Surface water samples were collected from 101 (85 river, 16 lake/reservoir) sites across the state at base-flow conditions for estrogenicity bioassay screening. Detectable estrogenicity was observed at 90% of the sites and 64% were above the US Environmental Protection Agency trigger level of 1 ng/L. Median surface water estrogenicity was 1.8 ng/L and a maximum of 6.9 ng/L E2EqBLYES was observed. Adult smallmouth bass were collected from nine sites, pre-spawn during the spring of 2017. Intersex was identified in fish at all sites, and the composite intersex prevalence was 93.8%. Prevalence across sites ranged from 70.6% to 100%. In addition to intersex, there was detectable plasma vitellogenin in males at all sites. Total estrogenicity in surface water was determined at these fish collection sites, and notable change over time was observed. Correlation analysis indicated significant positive correlations between land use (altered land; urban + agriculture) and surface water estrogenicity. There were no clear associations between land use and organismal metrics of estrogenic endocrine disruption (intersex or vitellogenin). This work establishes a baseline prevalence of intersex in male smallmouth bass in the state of New Jersey at a limited number of locations and identifies a number of waterbodies with estrogenic activity above an effects-based threshold.

An experimental study to evaluate predation threats on two native larval lampreys in the Columbia River Basin, USA

AbstractExperimental predation studies were conducted to evaluate and compare the predation threats of 10 species of native and non‐native fishes on larvae of Pacific Lamprey, Entosphenus tridentatus, and Western Brook Lamprey, Lampetra richardsoni. The relative predatory threats were examined over four sets of binary factors, including the following: (a) short (2‐day) or long (7‐day) duration, (b) presence/absence of fine sediment, (c) live or dead larvae and (d) species of lampreys. Our short‐term results showed a positive correlation with the sizes of predator fishes and consumed lamprey larvae. Also, most predator fishes had a significantly higher propensity to prey on lamprey larvae when sediment was absent. Conversely, this demonstrated the importance of sediment in protecting lamprey larvae from predation. Based on the predatory behaviour for live and dead larvae, predator fishes were classified into four groups using principal component analysis. Predation rates of larvae in sediment by piscivorous predators including Northern Pikeminnow Ptychocheilus oregonensis and Smallmouth Bass Micropterus dolomieu were lower and showed no differences even when the study duration was extended. In contrast, predation rates by benthic predators including White Sturgeon Acipenser transmontanus and Common Carp Cyprinus carpio, increased when we extended the study duration. This suggests that when given longer duration, benthic predators are more adept at consuming larvae within the sediment. These results provide important context for assessing the potential threat of predation on lampreys in streams, which is a key knowledge gap for lampreys.

Histopathologic Prevalence and Severity of Testicular Oocytes in Smallmouth Bass from Two Archival Collections.

During recent decades, survey studies have documented the widespread presence of oocytes in the testes of male Smallmouth Bass Micropterus dolomieu collected from surface waters throughout the United States. There are few published reports of testicular oocytes (TO) in Smallmouth Bass before the 1990s, so it is difficult to know how long this has been occurring. Consequently, this study was conducted to evaluate the prevalence and severity of TO occurrence in whole fish specimens from two archival collections-the Smithsonian Institution's National Museum of Natural History in Suitland, Maryland, and Cornell University's Museum of Vertebrates in Ithaca, New York. Gonads were excised from 167 preserved male Smallmouth Bass that were originally collected between 1875 and 2004, and routine histologic sections were prepared and examined. The severity of TO was determined using a semiquantitative scoring system. Overall, 52.1% of male Smallmouth Bass were found to have TO. Affected fish had been collected in 11 of the 18 represented states, and TO were found in specimens harvested during decades as early as the 1880s and 1900s. Unfortunately, the small number of samples acquired at the earliest time periods precluded analyses of prevalence and severity trends over time. The results of this study demonstrated that the phenomenon of TO in male Smallmouth Bass is at least a century old and confirmed the widespread nature of this finding throughout the species' historic range. Further research efforts should focus on determining the baseline prevalence of TO in laboratory-reared male Smallmouth Bass that have not been exposed to endocrine active substances or the effects of experimental estrogen exposure on such fish.

Space invaders: Searching for invasive Smallmouth Bass (Micropterus dolomieu) in a renowned Atlantic Salmon (Salmo salar) river.

Humans have the ability to permanently alter aquatic ecosystems and the introduction of species is often the most serious alteration. Non‐native Smallmouth Bass (Micropterus dolomieu) were identified in Miramichi Lake c. 2008, which is a headwater tributary to the Southwest Miramichi River, a renowned Atlantic Salmon (Salmo salar) river whose salmon population is dwindling. A containment programme managed by the Department of Fisheries and Oceans, Canada (DFO) was implemented in 2009 to confine Smallmouth Bass (SMB) to the lake. We utilized environmental DNA (eDNA) as a detection tool to establish the potential escape of SMB into the Southwest Miramichi River. We sampled at 26 unique sites within Miramichi Lake, the outlet of Miramichi Lake (Lake Brook), which flows into the main stem Southwest Miramichi River, and the main stem Southwest Miramichi River between August and October 2017. We observed n = 6 positive detections located in the lake, Lake Brook, and the main stem Southwest Miramichi downstream of the lake. No detections were observed upstream of the confluence of Lake Brook and the main stem Southwest Miramichi. The spatial pattern of positive eDNA detections downstream of the lake suggests the presence of individual fish versus lake‐sourced DNA in the outlet stream discharging to the main river. Smallmouth Bass were later confirmed by visual observation during a snorkeling campaign, and angling. Our results, both eDNA and visual confirmation, definitively show Smallmouth Bass now occupy the main stem of the Southwest Miramichi.

Fish life history trends indicate increasing flow stochasticity in an unregulated river

AbstractLife history theory provides a framework to understand environmental change based on species traits that capitalize on stable, predictable, or stochastic environmental conditions. We evaluated life history strategies and temporal trends in abundance from 1975 to 2017 for 28 fish species within the Potomac River of eastern North America. Multivariate analysis identified life history strategies defined by small‐bodied species with extended spawning seasons and early maturation (opportunistic strategists), large‐bodied species with delayed maturation and long lifespans (periodic strategists), and intermediate‐sized species exhibiting parental care (equilibrium strategists). Linear mixed models detected temporal trends in abundance for 13 species (46%), of which nine increased and four decreased over time. Increasing species were characterized by opportunistic life history strategies (e.g., banded killifish, Fundulus diaphanous; mosquito fish, Gambusia holbrooki), whereas decreasing species were characterized by periodic or equilibrium strategies (e.g., smallmouth bass, Micropterus dolomieu; river chub, Nocomis micropogon). Recent introductions can account for temporal increases in some cases, but most increasing species are native to the study area. Observed increases in opportunistic native species and decreases in periodic and equilibrium species indicate that environmental conditions have become less stable and less predictable over time, consistent with observed increases in spring peak flows in the study area. Our study indicates the importance of environmental stochasticity for fish community responses to land use and climate change and demonstrates the utility of life history theory in this regard.

Temporal trends in fish mercury concentrations in an Adirondack Lake managed with a continual predator removal program.

Mercury is a neurotoxic pollutant and contamination in remote ecosystems due to atmospheric mercury deposition coupled with watershed characteristics that influence mercury bioavailability. Biological interactions that affect mercury bioaccumulation are especially relevant as fish assemblages change in response to species introductions and lake management practices. We studied the influence of shifting food web dynamics on mercury in fisheries of Little Moose Lake in the southwestern Adirondack Mountains of New York, USA. Annual removal of non-native Smallmouth Bass (Micropterus dolomieu) has been used as a management strategy since 2000 to restore the native fish assemblage and food web in favor of Lake Trout (Salvelinus namaycush). Changes in total mercury, stable carbon (13C/12C) and nitrogen (15N/14N) isotopes, and growth were evaluated for Lake Trout and Smallmouth Bass. Growth rates increased for both predators and trophic position increased for Lake Trout post-removal. Mercury concentrations in Lake Trout increased over the 16-year study period influenced by a diet shift from invertebrates to higher trophic level prey fish, regardless of increased growth. Smallmouth Bass mercury concentrations decreased with compensatory growth from a reduced population size. These contrasting trends indicate that changes in mercury deposition were not the primary driver for mercury bioaccumulation responses in Little Moose Lake. Stable isotope values changed for both predators and for several lower trophic level organisms, likely reflecting changes in nutrient cycling and/or inputs. Our findings emphasize the potential role of fisheries management on whole-lake and predatory fish responses to mercury contamination in temperate lakes.

Behavioral responses of northern crayfish (Faxonius virilis) to conspecific alarm cues and predator cues from smallmouth bass (Micropterus dolomieu)

ABSTRACTWhile the ability for crayfish to detect visual and chemical cues is well documented, relatively few studies have probed the behavioral responses of crayfish to cues from key predators that they encounter in natural environments. Therefore, we examined how northern crayfish (Faxonius virilis) (Hagen 1870) responded to (1) alarm cues from conspecifics versus chemical cues from smallmouth bass (Micropterus dolomieu) (Lacepéde 1802), (2) varying concentrations of alarm cue from conspecifics, and lastly (3) smallmouth bass visual cues, chemical cues, and a combination of the two. We found that crayfish reduced walking activity in the presence of alarm cues. Chemical cues from smallmouth bass were also capable of eliciting a behavioral response, both alone and when paired with visual cues. Understanding the behavioral mechanisms by which crayfish respond to predatory fish is important to managing freshwater systems in the context of ongoing human- and climate-aided range expansions of both taxa.

An Assessment of the Thiamine Status of Smallmouth Bass (Micropterus dolomieu) in the Susquehanna River Watershed

Unpredictable recruitment and physical abnormalities (sores and lesions) have been observed in populations of Micropterus dolomieu (Smallmouth Bass) throughout the Susquehanna River basin. Malnutrition has been proposed as one of among several potential stressors, yet little to no information was available to critically assess its feasibility as a causal factor. We measured thiamine profiles of Smallmouth Bass (free thiamine [T], thiamine monophosphate [TP], and thiamine pyrophosphate [TPP]) for 3 tissues (egg, liver, and muscle) collected at 13 sites in the Susquehanna River and compared the values to those in 2 neighboring drainages (Allegheny River and Delaware River). Mass-specific thiamine concentrations in eggs were comparable to published values for Micropterus salmoides (Largemouth Bass), but higher than those found in Sander vitreus (Walleye), and Salvelinus namaycush (Lake Trout) known to consume Alosa pseudoharengus (Alewife), a thiaminase positive forage fish. In general, Smallmouth Bass collected from sites within the Susquehanna River basin had thiamine concentrations comparable to fish at the site in the Allegheny River, yet average thiamine concentrations in fish from the Susquehanna and Allegheny sites were each considerably lower than the average value collected from the Smallmouth Bass in the Delaware River. Future studies should consider a more balanced sampling design among watersheds to assess spatial variability among sites and basins. Average site-specific thiamine concentrations measured in Smallmouth Bass exceeded published minimum threshold values for Lake Trout. Given that Smallmouth Bass appear to have distinct thiamine profiles, concentrations, and timing of egg development, threshold thiamine concentrations parameterized for salmonids may not apply to Smallmouth Bass. As such, empirical studies that parameterize species-specific thiamine thresholds are needed to formally evaluate if thiamine deficiency is an issue for Smallmouth Bass in the Susquehanna River basin. To our knowledge, these are the first data on thiamine concentrations published for Smallmouth Bass.

Modified QuEChERS extraction for the analysis of young-of-year smallmouth bass using GC × GC-TOFMS.

Signs of disease, such as external lesions, have been prevalent in smallmouth bass throughout the Susquehanna River Basin, USA. Previous targeted chemical studies in this system have identified known persistent organic pollutants, but a common explanatory link across multiple affected sites remains undetermined. A fast and robust extraction method that can be applied to young-of-year fish is needed to effectively screen for target and non-target compounds that may be impacting organism health. The quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction methodology was optimized to perform both targeted and non-targeted chemical analyses from a single extraction of whole young-of-year fish. Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC × GC-TOFMS) was used for extract analysis. Sample extraction was performed using the solvent ethyl acetate, followed by a two-step cleanup in which samples were frozen for lipid removal and subjected to dispersive solid phase extraction using Florisil. A sample of 21 young-of-year smallmouth bass collected from areas with disease and exhibiting different types of external lesions were evaluated for 233 target compounds. A total of 34 organic contaminants, including polychlorinated biphenyls, brominated diphenyl ethers, organochlorinated pesticides, and personal care products, were detected. Data from this sample set was then analyzed for non-targets. Using the Fisher ratio method and multivariate analysis, an additional 10 significant features were identified specific to either fish with visible lesions or with no visible disease characteristics.

The Heart of the Lakes: Freshwater in the Past, Present, and Future of Southeast Michigan by Dave Dempsey

Book Reviews 177 commanding officer, Norval Welch, along with several dozen of his men, cast a shadow over the unit. At Petersburg a year later, the regiment led a successful charge on a Confederate earthwork that cost Welch his life but probably redeemed his good name among his men. The 16th Michigan Infantry in the Civil War (Revised and Updated) includes an impressive gallery of 84 soldier photographs, extensive endnotes, and a complete, annotated roster. Unfortunately, five fine battle maps that were commissioned for the 2002 version were not available for this edition. The lack of maps is the only serious drawback in this volume. Throughout the narrative, the author strikes a nice balance between writing for the campaign-hardened Civil War enthusiast and taking the time to provide brief explanations for the less experienced genealogist or generalist for whom this type of regimental history might be unfamiliar subject matter. This is a fine regimental history that will stand the test of time. Thomas P. Nanzig Ann Arbor Civil War Round Table Dave Dempsey. The Heart of the Lakes: Freshwater in the Past, Present, and Future of Southeast Michigan. East Lansing: Greenstone Books, 2019. Pp. 130. Bibliography. Illustrations. Notes. Paper: $19.95. Between southeast Michigan and southwest Ontario flows a ninetymile freshwater passage linking Lake Huron with Lake Erie. The two rivers (the St. Clair and the Detroit), one lake (St. Clair), and their network of tributaries and wetlands form the hydrological and commercial center of the Great Lakes system. Here, water from three upper lakes funnels into a fourth on its way to the lower Lake Ontario. Here, freighters running cargo south from the Upper Midwest pass those issuing north from the Saint Lawrence Seaway. But in The Heart of the Lakes, environmental writer and policy expert Dave Dempsey frames this corridor as much more than a conduit. Abundant water also attracted settlers and enabled development. Fur and salt traders, farmers and pharmacists, saw and steel millers, shipbuilders and automakers all located here. Environmental problems followed. Since the 1960s, residents have cooperated—though, perhaps, not often enough—across political and demographic divides to restore the region’s water resources. These people, working together toward a common goal, are the beating heart of the lakes. 178 The Michigan Historical Review Five geographically organized chapters and an epilogue unfurl the use, abuse, and (ongoing) recovery of this waterway. Chapter One condenses the ten millennia from the Last Glacial Period up to the early 1600s. Once oriented in geological time and space, we hit the water. Four successive chapters carry us down the St. Clair River, across Lake St. Clair, past Detroit, and on down the Detroit River. As we travel, Dempsey sets histories of communities alongside remediation efforts. He tells of Anishinaabe settling rich river deltas and voyageurs gaping at natural beauty; of a storied smallmouth bass fishery, a failed brine well reinvented as a therapeutic spring, and a vessel that carried escaped slaves to freedom; of the erection of forts, canals, roads, bridges, dams, railways, amusement parks, and so many lighthouses; of industrial spills, mercury emissions, invasive species, riparian drainage, and the discharge of untreated sewage; of donations that funded a string of recreational parks and pathways along the river in downtown Detroit and an ambitious project to rehabilitate remnants of a unique ecosystem known as lake-plain prairie. Throughout this journey, we hug Michigan shores. Dempsey gestures to Sarnia and Windsor, but Canadian cities and tributaries, such as the Sydenham and Thames, go unexplored. After we disembark at Lake Erie’s North Maumee Bay, Dempsey offers reflection. His epilogue summarizes how Southeast Michigan bounced back from its environmental nadir, and it proposes policies that might help the region realize a “blue” future. Dempsey’s decision to tour this water corridor brings both benefits and pitfalls. Fascinating historical sketches, told in clear prose, tie together the natural processes and human ambitions that shape this place. Not only should this book populate local libraries, Southeast Michiganders might stash it in their glove boxes, picnic baskets, and dry sacks for ready reference. However, profiling individual towns and attractions stifles the narrative, lending this slim volume the feel of a guidebook. At times...

Mercury increase in Lake Champlain fish: links to fishery dynamics and extreme climatic events.

Mercury concentrations in Lake Champlain fish increased (2011-2017) for the first time in more than two decades. The increase, however, was not consistent among species or throughout the lake. Mercury concentrations in smallmouth bass and yellow perch from the three Main Lake segments increased significantly while concentrations in the eastern portions of the lake (Northeast Arm and Malletts Bay) remained unchanged or decreased; mercury concentrations in white perch remained unchanged. Factors examined to explain the increase included: atmospheric deposition, lake temperature, chlorophyll-a, fishery dynamics, lake flooding and loading of total suspended solids (TSS). This paper examines how each factor has changed between study periods and the spatial variability associated with the change. We hypothesize fishery dynamics, flooding and TSS loading may be partially responsible for the increase in fish mercury. Both growth efficiency and biomass of fish suggest mercury concentrations would increase in the Main Lake segments and decrease in the eastern portion of the lake. Additionally, two extreme climate events in 2011 resulted in extensive flooding and a four-fold increase in annual TSS loading, both potentially increasing biotic mercury with the impact varying spatially throughout the lake. Changes to the fishery and disturbance caused by extreme climatic events have increased biotic mercury and the processes responsible need further study to identify possible future scenarios in order to better protect human and wildlife health.

Invasive Snakehead and Introduced Sport Fish Illustrate an Environmental Health Paradox of Invasive Species and Angler Demand

The invasive snakehead fish, which is native to Africa, Asia, Indonesia, and Malaysia, has been found in nine states in the United States and has notably developed a reproducing population in South Florida, Maryland, and Hawaii. This case study discusses the environmental impact and policies surrounding the snakehead fish population in the United States’ waters, as well as three other fishes (smallmouth bass, largemouth bass, and trout) that are native to some bodies of water in the United States, but non-native to others. This case study will examine the paradox that exists when the support of anglers and/or other important stakeholders in wildlife management does not match the potential a species has to damage a native habitat. Readers should be able to think critically about how people have come to define what is seemingly good for the environment based on personal human interest rather than environmental interest. They should also think about how easily the environment can be changed, even permanently, due to small cases of invasive species spreading rapidly from human practices.

Movement Dynamics of Smallmouth Bass in a Large Western River System

AbstractThe Snake River, Idaho, between Swan Falls and Brownlee dams supports a popular fishery for Smallmouth Bass Micropterus dolomieu. Recently, anglers have expressed concern about harvest of Smallmouth Bass associated with seasonal congregations in and near the lower reaches of several major tributaries. Little is known about Smallmouth Bass movement in the system, and a better understanding of movement dynamics will help to guide future management. From March to August 2016, Smallmouth Bass (≥260 mm; n = 1,131) were tagged with T‐bar anchor tags to evaluate large‐scale movement patterns. Movement was estimated from 63 angler‐reported tags for which area descriptions provided sufficient detail to assign a recapture location. Extent of fish movement varied among segments and tributaries from 0 to 128 river kilometers (rkm). From March to May 2017, Smallmouth Bass (≥305 mm; n = 149) in the Snake, Boise, Payette, and Weiser rivers and in Brownlee Reservoir were implanted with radio transmitters. Of the 149 Smallmouth Bass that were released with radio transmitters, 107 were relocated at least once. Additionally, 79.6% of fish with radio transmitters had a maximum extent of movement of 5 rkm or greater and 42.6% had a maximum extent of 30 rkm or greater; one radio‐tagged fish moved 167 rkm upstream. Average daily movement of Smallmouth Bass varied among river segments and was greatest in the spring and summer. Fish from the Snake River, tributaries (e.g., Boise River), and Brownlee Reservoir moved all around the study area, indicating an absence of clear population boundaries. As such, Smallmouth Bass in the study area appear to function as one large population as opposed to multiple subpopulations, thereby indicating that management as one population is likely appropriate.

Post-tournament dispersal of smallmouth bass in western Lake Erie

Catch-and-release tournaments for smallmouth bass Micropterus dolomieu transport fish from many capture locations to a centralized release site. In the Great Lakes, these fish may be transported long distances (i.e., >100 km) and subsequently become concentrated at a release site, possibly negatively affecting subpopulations at popular fishing sites if fish remain concentrated in the area. To assess timing of post-tournament dispersal, 23 smallmouth bass were implanted with acoustic transmitters and released into Sandusky Bay (Lake Erie) after a large tournament (50 boats) in September 2018. Tagged fish were tracked via a grid of acoustic receivers. All surviving fish (n = 19) left the immediate vicinity of the release site (<500 m) after an average (±SE) of 13.2 (±2.4) d, with many (58%) returning to the main lake (19.7 d ± 3.4). Eight (42%) of the surviving fish left the release site but remained in the bay after 50 d. Based on the results from this study, long-term (>1 month) concentration of smallmouth bass at release sites is unlikely to be a problem for Lake Erie bass tournaments, but temporary (up to 1 month) accumulations of fish are possible. A fraction of tournament-released smallmouth bass resided in Sandusky Bay for extended periods (>2 months), which could be considered functionally harvested from main lake subpopulations. Currently, the frequency of bass tournaments on Lake Erie is uncertain, and better documentation of tournament frequency and scale is necessary to assess potential negative impacts on bass populations.

Pumpkinseed sunfish (Lepomis gibbosus) counter spiny cladoceran (Bythotrephes longimanus) defenses

How do native species react to the presence of an invader? Consumption by resident fish is important in determining the yearly mortality of the invasive cladoceran Bythotrephes. In aquarium experiments, we discovered that small pumpkinseed sunfish (Lepomis gibbosus) were efficient at removing spines from Bythotrephes longimanus and consuming the adults. Experiments quantified how frequently pumpkinseeds showed successful removal of spines, and compared predatory performance relative to other species of fish. We also checked if Bythotrephes' resting eggs pass through the guts of pumpkinseeds in viable condition. The experiments revealed that pumpkinseed sunfish (45–70 mm total length, TL) from two geographic regions removed spines 87% of the time. Spine-handling techniques allowed pumpkinseeds to consume Bythotrephes faster than other species of small (<70 mm, TL) fish [yellow perch (Perca flavescens) and smallmouth bass (Micropterus dolomieu)]. Forty three percent of Bythotrephes’ resting eggs fed to pumpkinseeds passed through digestive systems intact, a property shared with other fish species. Our findings suggest that a native fish that possesses specialized morphology and behavior for hard-shelled prey manipulation (mollusk consumption) is pre-adapted to counter Bythotrephes’ spine defense. The studies raise two questions: 1) to what degree does pumpkinseed predation influence the geographic distribution of Bythotrephes, and 2) could pumpkinseeds become an effective biological control agent?

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.

Mercury in the fish of New York's Great Lakes: A quarter century of near stability.

We collected 849 fish of 16 species from New York portions of Lake Erie, Lake Ontario and the intervening Niagara River and its tributary Cayuga Creek, and analyzed fillets from individual fish for total mercury. Concentrations ranged from 0.029 to 1.090 ppm wet weight, with 92% below the EPA tissue residue criterion of 0.3 ppm, and thus not posing an undue risk from human consumption. We compared these 2010-2017 results to historical data spanning 40 years to assess temporal changes. The temporal pattern was generally consistent among water bodies and species: Mercury concentrations differed little between the most recent collections and fish taken from 1999-2008 and 1988-1996, while concentrations in all three of these periods were generally lower than in 1970. Smallmouth Bass from Lake Ontario were an exception with a continued decline, likely due to diet change following the introduction of exotic prey. Overall, though, fish tissue mercury concentrations from these large water bodies, which integrate regional influences, appear to have changed little in the last quarter century. We also report a consistent spatial pattern for multiple species having lower mercury concentrations in Lake Erie than in Lake Ontario over the period of record.