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At least 1,603 records · Page 89Linked to original sources

USGS2018

Blurred lines: Multiple freshwater and marine algal toxins at the land-sea interface of San Francisco Bay, California

San Francisco Bay (SFB) is a eutrophic estuary that harbors both freshwater and marine toxigenic organisms that are responsible for harmful algal blooms. While there are few commercial fishery harvests within SFB, recreational and subsistence harvesting for shellfish is common. Coastal shellfish are monitored for domoic acid and paralytic shellfish toxins (PSTs), but within SFB there is no routine monitoring for either toxin. Dinophysis shellfish toxins (DSTs) and freshwater microcystins are also present within SFB, but not routinely monitored. Acute exposure to any of these toxin groups has severe consequences for marine organisms and humans, but chronic exposure to sub-lethal doses, or synergistic effects from multiple toxins, are poorly understood and rarely addressed. This study documents the occurrence of domoic acid and microcystins in SFB from 2011 to 2016, and identifies domoic acid, microcystins, DSTs, and PSTs in marine mussels within SFB in 2012, 2014, and 2015. At least one toxin was detected in 99% of mussel samples, and all four toxin suites were identified in 37% of mussels. The presence of these toxins in marine mussels indicates that wildlife and humans who consume them are exposed to toxins at both sub-lethal and acute levels. As such, there are potential deleterious impacts for marine organisms and humans and these effects are unlikely to be documented. These results demonstrate the need for regular monitoring of marine and freshwater toxins in SFB, and suggest that co-occurrence of multiple toxins is a potential threat in other ecosystems where freshwater and seawater mix.

California↗

USGS2021

Domoic acid and saxitoxin in seabirds in the United States between 2007 and 2018

As harmful algal blooms (HABs) increase in magnitude and duration worldwide, they are becoming an expanding threat to marine wildlife. Over the past decade, blooms of algae that produce the neurotoxins domoic acid (DA) and saxitoxin (STX) and documented concurrent seabird mortality events have increased bicoastally in the United States. We conducted a retrospective analysis of HAB related mortality events in California, Washington, and Rhode Island between 2007 and 2018 involving 12 species of seabirds, to document the levels, ranges, and patterns of DA and STX in eight sample types (kidney, liver, stomach, intestinal, cloacal, cecal contents, bile, blood) collected from birds during these events. Samples ( n = 182 ) from 83 birds were examined for DA ( n = 135) or STX ( n = 17) or both toxins simultaneously ( n = 30), using ELISA or LCMS at the National Oceanographic and Atmospheric Administration, National Marine Fisheries Service (NOAA-NMFS) Wildlife Algal-toxin Research and Response Network (WARRN-West) or the University of California, Santa Cruz (UCSC). DA or STX was detected in seven of the sample types with STX below the minimum detection limit in blood for the three samples tested. DA was found in 70% and STX was found in 23% of all tested samples. The ranges of detectable levels of DA and STX in all samples were 0.65–681,190.00 ng g −1 and 2.00–20.95 ng g −1 , respectively. Cloacal contents from a Pacific loon ( Gavia pacifica ) collected in 2017 from Ventura County, California, had the highest maximum level of DA for all samples and species tested in this study. The highest level of STX for all samples and species was detected in the bile of a northern fulmar ( Fulmarus glacialis ) collected in 2018 from San Luis Obispo County, California. DA detections were consistently found in gastrointestinal samples, liver, bile, and kidney, whereas STX detections were most frequently seen in liver and bile samples. Co-occurring HAB toxins (DA and STX) were detected in white-winged scoters ( Melanitta deglandi ) in 2009, a Brandt's cormorant ( Phalacrocorax penicillatus ) in 2015, and a northern fulmar and common murre ( Uria aalge ) in 2018. This article provides DA and STX tissue concentrations and patterns in avian samples and shows the utility of various sample types for the detection of HAB toxins. Future research to understand the pharmacodynamics of these toxins in avian species and to establish lethal doses in various bird species would be beneficial.

Harmful Algae↗

USGS2013

Semi-automted analysis of high-resolution aerial images to quantify docks in Upper Midwest glacial lakes

Lake resources can be negatively affected by environmental stressors originating from multiple sources and different spatial scales. Shoreline development, in particular, can negatively affect lake resources through decline in habitat quality, physical disturbance, and impacts on fisheries. The development of remote sensing techniques that efficiently characterize shoreline development in a regional context could greatly improve management approaches for protecting and restoring lake resources. The goal of this study was to develop an approach using high-resolution aerial photographs to quantify and assess docks as indicators of shoreline development. First, we describe a dock analysis workflow that can be used to quantify the spatial extent of docks using aerial images. Our approach incorporates pixel-based classifiers with object-based techniques to effectively analyze high-resolution digital imagery. Second, we apply the analysis workflow to quantify docks for 4261 lakes managed by the Minnesota Department of Natural Resources. Overall accuracy of the analysis results was 98.4% (87.7% based on ) after manual post-processing. The analysis workflow was also 74% more efficient than the time required for manual digitization of docks. These analyses have immediate relevance for resource planning in Minnesota, whereas the dock analysis workflow could be used to quantify shoreline development in other regions with comparable imagery. These data can also be used to better understand the effects of shoreline development on aquatic resources and to evaluate the effects of shoreline development relative to other stressors.

Minnesota↗

USGS2005

Resilience of predators to fishing pressure on coral patch reefs

Numbers and biomass of piscivorous fish and their predation on other fish may often be high in undisturbed coral reef communities. The effects of such predation have sometimes been studied by removal of piscivores (either experimentally or by fishermen). Such perturbations have usually involved removal of large, highly vulnerable, mobile piscivores that are often actively sought in fisheries. The effects of fishing on smaller, demersal, semi-resident piscivores have been little studied. We studied such effects on the fish communities of patch reefs at Midway atoll by experimentally removing major resident, demersal, piscivorous fishes. First, four control reefs and four experimental reefs were selected, their dimensions and habitats mapped, and their visible fish communities censused repeatedly over 1 year. Census of all control and experimental reefs was continued for the following 39 months, during which known piscivores were collected repeatedly by hand spearing. Records were kept of catch and effort to calculate CPUE as an index of predator density. Spearfishing on the experimental reefs removed 2504 piscivorous fish from 12 families and 43 taxa (mostly species). The species richness of the catch did not show an overall change over the duration of the experiment. Spearman rank correlation analysis showed some unexpected positive correlations for density in numbers and biomass of major fished piscivorous groups (especially lizardfish) over the experiment. Only two relatively minor fished piscivorous taxa declined in abundance over the experiment, while the overall abundance of piscivores increased. Visual censuses of fish on the experimental reefs also failed to show reduction of total piscivores over the full experimental period. No significant trend in the abundance of lizardfish censused over the full period was apparent on any of the control reefs. The high resilience of piscivores on these experimental reefs to relatively intense fishing pressure could result from their protracted recruitment seasons, high immigration rates, cryptic habits, or naturally high abundances. A major factor was the high immigration rates of lizardfish, replacing lizardfish and other less mobile piscivores removed from the reefs by spearing. On the fished reefs, the removed lizardfish population replaced itself >20 times during the experiment; other piscivorous taxa replaced themselves only 5 times.

Journal of Experimental Marine Biology and Ecology↗

USGS2007

Ecological observations on the colonial ascidian Didemnum sp. in a New England tide pool habitat

The colonial ascidian Didemnum sp. has colonized northwestern Atlantic coastal habitats from southern Long Island, New York, to Eastport, Maine. It is also present in offshore habitats of the Georges Bank fishing grounds. It threatens to alter fisheries habitats and shellfish aquacultures. Observations in a tide pool at Sandwich, MA from December 2003 to February 2006 show that Didemnum sp. tolerates water temperatures ranging from ≤ 1 to > 24 °C, with daily changes of up to 11 °C. It attaches to pebbles, cobbles, and boulders, and it overgrows other tunicates, seaweeds, sponges, and bivalves. From May to mid July, colonies appear as small patches on the bottoms of rocks. Colonies grow rapidly from July to September, with some growth into December, and they range in color from pink to pale yellow to pale orange. Colony health declines from October through April, presumably in response to changes in water temperatures, and this degenerative process is manifested by color changes, by the appearance of small dark brown spots that represent clumps of fecal pellets in the colony, by scavenging by periwinkles, and by a peeling-away of colonies from the sides of cobbles and boulders. At Sandwich, colonies died that were exposed to air at low tide. The species does not exhibit this seasonal cycle of growth and decline in subtidal habitats (40–65 m) on the Georges Bank fishing grounds where the daily climate is relatively stable and annual water temperatures range from 4 to 15 °C. Experiments in the tide pool with small colony fragments (5 to 9 cm 2 ) show they re-attach and grow rapidly by asexual budding, increasing in size 6- to 11-fold in the first 15 days. Didemnum sp. at Sandwich has no known predators except for common periwinkles ( Littorina littorea ) that graze on degenerating colonies in the October to April time period and whenever colonies are stressed by desiccation. The tendencies of the ascidian (1) to attach to firm substrates, (2) to rapidly overgrow other species, (3) to tolerate a wide temperature range, (4) to be free from predation, and (5) to spread by colony fragmentation combine to make it a potential threat to benthic marine habitats and aquacultures. Didemnum sp. is known to overgrow mussels, oysters, and sea scallops, and it likely envelops other bivalves too.

Massachusetts↗

USGS2014

Unique characteristics of the trachea of the juvenile leatherback turtle facilitate feeding, diving and endothermy

The adult leatherback turtle Dermochelys coriacea overlaps in body size (300–500 kg) with many marine mammals, yet develops from a 50 g hatchling. Adults can dive deeper than 1200 m and have core body temperatures of 25 °C; hatchlings are near-surface dwellers. Juvenile leatherbacks have rarely been studied; here we present anatomical information for the upper respiratory tract of 3 turtles (66.7–83.0 cm straight carapace length; 33.2–53.4 kg body mass) incidentally captured by long-line fisheries. Combined with existing information from adults and hatchlings, our data show that there is an ontogenic shift in tracheal structure, with cartilaginous rings becoming broader and eventually fusing anteriorly. This ontogenic shift during independent existence is unique among extant deep-diving air breathing vertebrates. Tract wall thickness is graded, becoming progressively thinner from larynx to bronchi. In addition, cross-sectional shape becomes increasingly dorsoventrally flattened (more elliptical) from anterior to posterior. These characteristics ensure that the tract will collapse from posterior to anterior during dives. This study contains the first report of a double (= internally bifurcated) posterior section of the trachea; it is suggested that this allows continuous food movement along the esophagus without tracheal collapse. The whole upper respiratory tract (from larynx to lungs) has a vascular lining (thicker anteriorly than posteriorly) that appears to be a simple analog of the complex turbinates of birds and mammals. Our study confirmed that the leatherback tracheal structure represents a distinctive way of dealing with the challenges of diving in deep, cold sea water.

Journal of Experimental Marine Biology and Ecology↗

USGS2017

Loss of ecosystem services due to chronic pollution of forests and surface waters in the Adirondack region (USA)

Sustaining recent progress in mitigating acid pollution could require lower emissions caps that will give rise to real or perceived tradeoffs between healthy ecosystems and inexpensive energy. Because most impacts of acid rain affect ecosystem functions that are poorly understood by policy-makers and the public, an ecosystem services (ES) framework can help to measure how pollution affects human well-being. Focused on the Adirondack region (USA), a global ‘hot-spot’ of acid pollution, we measured how the chronic acidification of the region's forests, lakes, and streams has affected the potential economic and cultural benefits they provide to society. We estimated that acid-impaired hardwood forests provide roughly half of the potential benefits of forests on moderate to well-buffered soils – an estimated loss of ∼ $10,000 ha −1 in net present value of wood products, maple syrup, carbon sequestration, and visual quality. Acidic deposition has had only nominal impact – relative to the effects of surficial geology and till depth – on the capacity of Adirondack lakes and streams to provide water suitable for drinking. However, as pH declines in lakes, the estimated value of recreational fishing decreases significantly due to loss of desirable fish such as trout. Hatchery stocking programs have partially offset the pollution-mediated losses of fishery value, most effectively in the pH range 4.8–5.5, but are costly and limited in scope. Although any estimates of the monetary ‘damages’ of acid rain have significant uncertainties, our findings highlight some of the more tangible economic and cultural benefits of pollution mitigation efforts, which continue to face litigation and political opposition.

New York↗

USGS2023

Coproduction and modeling spatial contact networks prevent bias about infectious hematopoietic necrosis virus transmission for Snake River Basin salmonids

Much remains unknown about variation in pathogen transmission across the geographic range of a free-ranging fish or animal species and about the influence of movement (associated with husbandry practices or animal behavior) on pathogen transmission. Salmonid hatcheries are an ideal system in which to study these processes. Salmonid hatcheries are managed for endangered species recovery, supplementation of threatened or at-risk fish stocks, support of fisheries, and ecosystem stability. Infectious hematopoietic necrosis virus (IHNV) is a rhabdovirus of significant concern to salmon aquaculture. Landscape IHNV transmission dynamics previously had been estimated only for salmonid hatcheries in the Lower Columbia River Basin (LCRB). The objectives of this study were to estimate IHNV transmission dynamics in a unique geographic region, the Snake River Basin (SRB), and to quantitatively estimate the effect of model coproduction on inference because previous assessments of coproduction have been qualitative. In contrast to the LCRB, the SRB has hatchery complexes consisting of a main hatchery and ≥1 satellite facility. Knowledge about hatchery complexes was held by a subset of project researchers but would not have been available to project modelers without coproduction. Project modelers generated and tested multiple versions of Bayesian susceptible-exposedinfected models to realistically represent the SRB and estimate the effect of coproduction. Models estimated the frequency of transmission routes, route-specific infection probabilities, and infection probabilities for combinations of salmonid hosts and IHNV lineages. Model results indicated that in the SRB, avoiding exposure to IHNV-positive adult salmonids is the most important action to prevent juvenile infections. Migrating adult salmonids exposed juvenile cohort-sites most frequently, and the infection probability was greatest following exposure to migrating adults. Without coproduction, the frequency of exposure by migrating adults would have been overestimated by 70 cohort-sites, and the infection probability following exposure to migrating adults would have been underestimated by∼0.09. The coproduced model had less uncertainty in the infection probability if no transmission route could be identified (Bayesian credible interval (BCI) width = 0.12) compared to the model without coproduction (BCI width = 0.34). Evidence for virus lineage MD specialization on steelhead and rainbow trout (both Oncorhynchus mykiss) was apparent without model coproduction. In the SRB, we found a greater probability of virus lineage UC infection in Chinook salmon (Oncorhynchus tshawytscha) compared to in O. mykiss, whereas in the LCRB, UC more clearly exhibited a generalist approach. Coproduction influenced estimates that depended on transmission routes, which operated differently at main hatcheries and satellite sites within hatchery complexes. Hatchery complexes are found outside of the SRB and are not specific to salmonid hatcheries alone. There is great potential for coproduction and modeling spatial contact networks to advance understanding about infectious disease transmission in complex production systems and surrounding free-ranging animal populations.

Idaho, Oregon, Washington↗

USGS2013

Gastric evacuation rate, index of fullness, and daily ration of Lake Michigan slimy sculpin (Cottus cognatus) and deepwater sculpin (Myoxocephalus thompsonii)

Accurate estimates of fish consumption are required to understand trophic interactions and facilitate ecosystem-based fishery management. Despite their importance within the food-web, no method currently exists to estimate daily consumption for Great Lakes slimy (Cottus cognatus) and deepwater sculpin (Myoxocephalus thompsonii). We conducted experiments to estimate gastric evacuation (GEVAC) and collected field data from Lake Michigan to estimate index of fullness [(g prey/g fish weight)100%) to determine daily ration for water temperatures ranging 2–5 °C, coinciding with the winter and early spring season. Exponential GEVAC rates equaled 0.0115/h for slimy sculpin and 0.0147/h for deepwater sculpin, and did not vary between 2.7 °C and 5.1 °C for either species or between prey types (Mysis relicta and fish eggs) for slimy sculpin. Index of fullness varied with fish size, and averaged 1.93% and 1.85% for slimy and deepwater sculpins, respectively. Maximum index of fullness was generally higher (except for the smallest sizes) for both species in 2009–2010 than in 1976 despite reductions in a primary prey, Diporeia spp. Predictive daily ration equations were derived as a function of fish dry weight. Estimates of daily consumption ranged from 0.2 to 0.8% of their body weight, which was within the low range of estimates from other species at comparably low water temperatures. These results provide a tool to estimate the consumptive demand of sculpins which will improve our understanding of benthic offshore food webs and aid in management and restoration of these native species in the Great Lakes.

Journal of Great Lakes Research↗

USGS2015

Stock-specific advection of larval walleye ( Sander vitreus ) in western Lake Erie: Implications for larval growth, mixing, and stock discrimination

Physical processes can generate spatiotemporal heterogeneity in habitat quality for fish and also influence the overlap of pre-recruit individuals (e.g., larvae) with high-quality habitat through hydrodynamic advection. In turn, individuals from different stocks that are produced in different spawning locations or at different times may experience dissimilar habitat conditions, which can underlie within- and among-stock variability in larval growth and survival. While such physically-mediated variation has been shown to be important in driving intra- and inter-annual patterns in recruitment in marine ecosystems, its role in governing larval advection, growth, survival, and recruitment has received less attention in large lake ecosystems such as the Laurentian Great Lakes. Herein, we used a hydrodynamic model linked to a larval walleye ( Sander vitreus ) individual-based model to explore how the timing and location of larval walleye emergence from several spawning sites in western Lake Erie (Maumee, Sandusky, and Detroit rivers; Ohio reef complex) can influence advection pathways and mixing among these local spawning populations (stocks), and how spatiotemporal variation in thermal habitat can influence stock-specific larval growth. While basin-wide advection patterns were fairly similar during 2011 and 2012, smaller scale advection patterns and the degree of stock mixing varied both within and between years. Additionally, differences in larval growth were evident among stocks and among cohorts within stocks which were attributed to spatiotemporal differences in water temperature. Using these findings, we discuss the value of linked physical–biological models for understanding the recruitment process and addressing fisheries management problems in the world's Great Lakes.

Journal of Great Lakes Research↗

USGS2015

Changes in the Lake Michigan food web following dreissenid mussel invasions: A synthesis

Using various available time series for Lake Michigan, we examined changes in the Lake Michigan food web following the dreissenid mussel invasions and identified those changes most likely attributable to these invasions, thereby providing a synthesis. Expansion of the quagga mussel ( Dreissena rostriformis bugensis ) population into deeper waters, which began around 2004, appeared to have a substantial predatory effect on both phytoplankton abundance and primary production, with annual primary production in offshore (> 50 m deep) waters being reduced by about 35% by 2007. Primary production likely decreased in nearshore waters as well, primarily due to predatory effects exerted by the quagga mussel expansion. The drastic decline in Diporeia abundance in Lake Michigan during the 1990s and 2000s has been attributed to dreissenid mussel effects, but the exact mechanism by which the mussels were negatively affecting Diporeia abundance remains unknown. In turn, decreased Diporeia abundance was associated with reduced condition, growth, and/or energy density in alewife ( Alosa pseudoharengus ), lake whitefish ( Coregonus clupeaformis ), deepwater sculpin ( Myoxocephalus thompsonii ), and bloater ( Coregonus hoyi ). However, lake-wide biomass of salmonines, top predators in the food web, remained high during the 2000s, and consumption of alewives by salmonines actually increased between the 1980–1995 and 1996–2011 time periods. Moreover, abundance of the lake whitefish population, which supports Lake Michigan's most valuable commercial fishery, remained at historically high levels during the 2000s. Apparently, counterbalancing mechanisms operating within the complex Lake Michigan food web have enabled salmonines and lake whitefish to retain relatively high abundances despite reduced primary production.

Lake Michigan↗

USGS2015

Changes in depth occupied by Great Lakes lake whitefish populations and the influence of survey design

Understanding fish habitat use is important in determining conditions that ultimately affect fish energetics, growth and reproduction. Great Lakes lake whitefish ( Coregonus clupeaformis ) have demonstrated dramatic changes in growth and life history traits since the appearance of dreissenid mussels in the Great Lakes, but the role of habitat occupancy in driving these changes is poorly understood. To better understand temporal changes in lake whitefish depth of capture ( D w ), we compiled a database of fishery-independent surveys representing multiple populations across all five Laurentian Great Lakes. By demonstrating the importance of survey design in estimating D w , we describe a novel method for detecting survey-based bias in D w and removing potentially biased data. Using unbiased D w estimates, we show clear differences in the pattern and timing of changes in lake whitefish D w between our reference sites (Lake Superior) and those that have experienced significant benthic food web changes (lakes Michigan, Huron, Erie and Ontario). Lake whitefish D w in Lake Superior tended to gradually shift to shallower waters, but changed rapidly in other locations coincident with dreissenid establishment and declines in Diporeia densities. Almost all lake whitefish populations that were exposed to dreissenids demonstrated deeper D w following benthic food web change, though a subset of these populations subsequently shifted to more shallow depths. In some cases in lakes Huron and Ontario, shifts towards more shallow D w are occurring well after documented Diporeia collapse, suggesting the role of other drivers such as habitat availability or reliance on alternative prey sources.

Lake Erie, Lake Huron, Lake Michigan, Lake Ontario↗

USGS2016

Telemetry narrows the search for sea lamprey spawning locations in the St. Clair-Detroit River System

Adult sea lamprey ( Petromyzon marinus ) abundance in Lake Erie has remained above targets set by fishery managers since 2005, possibly due to increased recruitment in the St. Clair-Detroit River System (SCDRS). Sea lamprey recruitment in the SCDRS poses an enormous challenge to sea lamprey control and assessment in Lake Erie because the SCDRS contains no dams to facilitate capture and discharge is at least an order of magnitude larger in the SCDRS than most other sea lamprey-producing tributaries in the Great Lakes. As a first step toward understanding population size, spatial distribution, and spawning habitat of adult sea lampreys in the SCDRS, we used acoustic telemetry to determine where sea lampreys ceased migration (due to spawning, death, or both) among major regions of the SCDRS. All tagged sea lampreys released in the lower Detroit River ( N = 27) moved upstream through the Detroit River and entered Lake St. Clair. After entering Lake St. Clair, sea lampreys entered the St. Clair River ( N = 22), Thames River ( N = 1), or were not detected again ( N = 4). Many sea lampreys (10 of 27) were last observed moving downstream (“fallback”) but we were unable to determine if those movements occurred before or after spawning, or while sea lampreys were dead or alive. Regardless of whether estimates of locations where sea lampreys ceased migration were based on the most upstream region occupied or final region occupied, most sea lampreys ceased migration in the St. Clair River or Lake St. Clair. Results suggest that spawning and rearing in the St. Clair River could be an important determinant of sea lamprey recruitment in the SCDRS and may direct future assessment and control activities in that system.

Michigan, Ontario↗

USGS2017

Exploring potential effects of cormorant predation on the fish community in Saginaw Bay, Lake Huron

Stakeholders and fishery managers expressed concern that double-crested cormorant Phalacrocorax auritus predation may be a factor in the recent poor survival of yellow perch Perca flavescens in Saginaw Bay. We quantified cormorant diets from two nesting colonies in Saginaw Bay during April–September in 2013 and 2014, with special emphasis on impacts to yellow perch. Cormorants ( n = 691) were collected when returning to colonies after foraging. Stomachs were removed and preserved in the field. Diet items were identified, enumerated, and measured ( n = 23.373). Cormorant diets from Saginaw Bay indicate a heavy reliance on round goby and Notropis species as prey during the breeding season, consistent with other areas of the Great Lakes where round goby and cormorants coincide. Respectively, the three most common prey species observed by number (%) and biomass (%) pooled across years and sites were round goby Neogobius melanostomus (56.6%, 42.1%), emerald shiner Notropis antherinoides (25.2%, 12.5%), and yellow perch (8.0%, 14.1%). Diet composition was more variable at Spoils Island than at Little Charity Island. Overall cormorant consumption (estimated using cormorant consumption demand rates) of yellow perch was compared to walleye consumption. Cormorant consumption of age-1 yellow perch was 13–17% as much as mean walleye consumption of yellow perch in 2013 and 8–11% in 2014. The cumulative effects of walleye and spring cormorant predation likely represent a recruitment bottleneck for yellow perch in Saginaw Bay. Future studies determining age-specific abundance of yellow perch would facilitate better determination of cormorant predation significance.

Lake Huron, Saginaw Bay↗

USGS2017

Asynchrony in the inter-annual recruitment of lake whitefish Coregonus clupeaformis in the Great Lakes region

Spatially separated fish populations may display synchrony in annual recruitment if the factors that drive recruitment success, particularly abiotic factors such as temperature, are synchronised across broad spatial scales. We examined inter-annual variation in recruitment among lake whitefish ( Coregonus clupeaformis ) populations in lakes Huron, Michigan and Superior using fishery-dependent and -independent data from 1971 to 2014. Relative year-class strength (RYCS) was calculated from catch-curve residuals for each year class across multiple sampling years. Pairwise comparison of RYCS among datasets revealed no significant associations either within or between lakes, suggesting that recruitment of lake whitefish is spatially asynchronous. There was no consistent correlation between pairwise agreement and the distance between datasets, and models to estimate the spatial scale of recruitment synchrony did not fit well to these data. This suggests that inter-annual recruitment variation of lake whitefish is asynchronous across broad spatial scales in the Great Lakes. While our method primarily evaluated year-to-year recruitment variation, it is plausible that recruitment of lake whitefish varies at coarser temporal scales (e.g. decadal). Nonetheless, our findings differ from research on some other Coregonus species and suggest that local biotic or density-dependent factors may contribute strongly to lake whitefish recruitment rather than inter-annual variability in broad-scale abiotic factors.

Great Lakes↗

USGS2017

Genetic structure of muskellunge in the Great Lakes region and the effects of supplementation on genetic integrity of wild populations

Muskellunge ( Esox masquinongy ) are important apex predators that support numerous recreational fisheries throughout the Great Lakes region. Declines in muskellunge abundance from historical overharvest and environmental degradation have threatened the viability of many populations and prompted significant restoration efforts that often include stocking. The goal of our study was to investigate contemporary population structure and genetic diversity in 42 populations of muskellunge sampled across the Great Lakes region to inform future management and supplementation practices. We genotyped 1896 muskellunge ( N = 10–123/population) at 13 microsatellite loci. The greatest genetic variation was between populations of Great Lakes origin and populations of Northern (inland) origin, with both groups also exhibiting significant substructure (overall F ST = 0.23). Genetic structure was generally correlated with geography; however, we only found marginal evidence of isolation by distance, likely due to high genetic differentiation among proximate populations. Measures of genetic diversity were moderate across most populations, but some populations displayed low diversity consistent with small population sizes or historical bottlenecks. Many of the populations studied displayed evidence of historic introductions and supplemental stocking, including the presence of individuals with primarily non-native ancestry as well as interlineage hybrids. Our results suggest that the historic population structure of muskellunge is largely intact across the Great Lakes region, but also that stocking practices have altered this structure to some degree. We suggest that future supplementation practices use local sources where possible, and incorporate genetic tools including broodstock screening to ensure that non-native muskellunge are not used to supplement wild populations.

Great Lakes↗

USGS2018

Evaluation of anal fin spines, otoliths, and scales for estimating age and back-calculated lengths of yellow perch in southern Green Bay

Southern Green Bay supports important fisheries for yellow perch Perca flavescens and valid estimates of age structure and growth are critical to effective management. Anal fin spines and scales are used by the Wisconsin Department of Natural Resources for age estimation, but these structures may provide lower precision and accuracy than otoliths. The primary objective of our assessment was to determine if age estimates, among-reader precision, and mean back-calculated total lengths (TLs) at age differed among scales, anal fin spines, and otoliths. Ages estimated from anal fin spines were more precise than scale ages, were as precise as otolith-based ages, and generally agreed with consensus ages estimated from sectioned otoliths. Relationships between TL and radii of calcified structures were linear for scales, anal spines, and otoliths along two different transects. Mean back-calculated TLs were generally similar between intercept-corrected direct proportion (ICDP) and linear regression (LR) models, but otolith-based direct proportion models (no intercept correction) generally provided higher back-calculated mean TLs at ages 1 and 2 than ICDP and LR models. Mean back-calculated TLs at age estimated from whole otoliths were higher than estimates for other structures; but differences among anal fin spines, scales, and sectioned otoliths were <10 mm. Our results suggest biologists have little to gain by switching to otoliths when assessing age structure and growth for this fast-growing yellow perch population with relatively few fish ≥age 6, but additional analyses are warranted for slower-growing perch populations in the Great Lakes where older fish are more common.

Wisconsin↗

USGS2018

Great Lakes coastal fish habitat classification and assessment

Basin-scale assessment of fish habitat in Great Lakes coastal ecosystems would increase our ability to prioritize fish habitat management and restoration actions. As a first step in this direction, we identified key habitat factors associated with highest probability of occurrence for several societally and ecologically important coastal fish species as well as community metrics, using data from the Great Lakes Aquatic Habitat Framework (GLAHF), Great Lakes Environmental Indicators (GLEI) and Coastal Wetland Monitoring Program (CWMP). Secondly, we assessed whether species-specific habitat was threatened by watershed-level anthropogenic stressors. In the southern Great Lakes, key habitat factors for determining presence/absence of several species of coastal fish were chlorophyll concentrations, turbidity, and wave height, whereas in the northern ecoprovince temperature was the major habitat driver for most of the species modeled. Habitat factors best explaining fish richness and diversity were bottom slope and chlorophyll a . These models could likely be further improved with addition of high-resolution submerged macrophytecomplexity data which are currently unavailable at the basin-wide scale. Proportion of invasive species was correlated primarily with increasing maximum observed inorganic turbidity and chlorophyll a . We also demonstrate that preferred habitat for several coastal species and high-diversity areas overlap with areas of high watershed stress. Great Lakes coastal wetland fish are a large contributor to ecosystem services as well as commercial and recreational fishery harvest, and scalable basin-wide habitat models developed in this study may be useful for informing management actions targeting specific species or overall coastal fish biodiversity.

Great Lakes↗