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At least 217 records · Page 12Linked to original sources

USGS2020

Effects of latitude, season, and temperature on Lake Sturgeon movement

Ecologists have a limited understanding of the rangewide variation in movement behavior in freshwater fishes, but recent expansion of biotelemetry allows biologists to investigate how fish movement can help to predict behavioral shifts in response to changing environments. The Lake Sturgeon Acipenser fulvescens is a wide-ranging, migratory, coolwater species, making it a candidate species for studying patterns in movement ecology. We conducted a literature review and meta-analysis of seasonal movement data compiled from 38 Lake Sturgeon telemetry studies in North America to build an understanding of spatiotemporal variation in movement behavior. Lake Sturgeon movement studies were underrepresented for low-latitude populations in the Mississippi, Missouri, and Ohio/Tennessee River basins. Highest movement usually occurred during spring spawning migrations, whereas other populations exhibited their highest movement in the fall, potentially in order to overwinter near spawning grounds. Our meta-regression analysis indicated that latitude or summer maximum temperature best predicted standardized mean difference between spring and summer movement in Lake Sturgeon populations across the species’ range. Our results suggest that Lake Sturgeon populations at lower latitudes and those that experience warmer summer temperatures have lower summer movement relative to spring movement. Managers may use this information to prioritize actions promoting the conservation of seasonally important habitats for the continued recovery of migratory coolwater fish (e.g., Lake Sturgeon) that potentially experience stressful thermal conditions.

North American Journal of Fisheries Management↗

USGS2008

Changes in consumption by alewives and lake whitefish after dreissenid mussel invasions in Lakes Michigan and Huron

Growth of alewives Alosa pseudoharengus and lake whitefish Coregonus clupeaformis has declined since the arrival and spread of dreissenid mussels in Lakes Michigan and Huron. Alewives are the main forage for the salmonids in Lake Michigan, and lake whitefish are the most important commercial species in both lakes. Bioenergetics modeling was used to determine consumption by the average individual fish before and after the dreissenid invasion and to provide insight into the invasion's effects on fish growth and food web dynamics. Alewives feed on both Zooplankton and benthic macroinvertebrates, and lake whitefish are benthivores. Annual consumption of zooplankton by an average alewife in Lake Michigan was 37% lower and consumption of benthic macroinvertebrates (amphipods Diporeia spp., opossum shrimp Mysis relicta, and Chironomidae) was 19% lower during the postinvasion period (1995-2005) than during the preinvasion period (1983-1994). Reduced consumption by alewives corresponded with reduced alewife growth. In Lakes Michigan and Huron, consumption of nonmollusk macroinvertebrates (Diporeia spp., opossum shrimp, Chironomidae) by the average lake whitefish was 46-96% lower and consumption of mollusks (mainly dreissenids and gastropods) was 2-5 times greater during the postinvasion period than during the preinvasion period. Even though total food consumption by lake whitefish did not differ between the two periods in Lake Huron or the Southern Management Unit in Lake Michigan, postinvasion weight at age was at least 38% lower than preinvasion weight at age. Under the current postinvasion diet regime, consumption by lake whitefish would have to increase by up to 122% to achieve preinvasion growth rates. ?? Copyright by the American Fisheries Society 2008.

North American Journal of Fisheries Management↗

USGS2020

Movement dynamics of nonnative Burbot in the upper Green River system and implications for management

Burbot Lota lota were illegally introduced to the Green River, Wyoming, in the mid-1990s and pose a threat to recreational fisheries and native fish conservation. Although much is known about Burbot population dynamics, little is known about their movement patterns. Our objectives were to describe the movement dynamics of Burbot in the upper Green River system to provide information on the ecology of Burbot and insight on possible management actions. In total, 875 Burbot were tagged with PIT tags in the upper Green River and Fontenelle Reservoir; their movements were tracked from August 2016 to March 2018. Additionally, 22 Burbot were tagged with radio transmitters in Fontenelle Reservoir in November 2017, and 13 Burbot were tagged with radio transmitters in the upper Green River in November 2018. Of these fish, 11 Burbot tagged in Fontenelle Reservoir and all river-tagged Burbot were tracked as they migrated into the Green River and associated tributaries during the spawning season. Upstream and downstream movements of Burbot tagged with PIT tags in Fontenelle Reservoir and the upper Green River peaked during December–January and were synchronized with river temperatures reaching 0°C. Of the total number of PIT-tagged Burbot, 10–15% of those tagged in Fontenelle Reservoir were detected in the Green River during the spawning season and 15% of those tagged in the Green River were detected moving downstream toward Fontenelle Reservoir during the spawning period. Movements of radiotelemetered Burbot were synchronized with river ice-up in mid-December. Maximum upstream distance traveled by adfluvial Burbot was 5.8 km. Fluvial Burbot primarily migrated downstream during the spawning period, and maximum downstream distance traveled was 17.7 km. Detection data suggest that both fluvial and adfluvial Burbot occupy the same reaches during the spawning period and areas near Fontenelle Reservoir are important for spawning. Results of this study will assist with the management of Burbot in this system by shedding light on Burbot movement patterns and identifying areas of high Burbot use for targeted suppression efforts. Results also contribute to our understanding of the variability in Burbot ecology.

Wyoming↗

USGS2021

Hydrologic effects on growth and hatching success of age-0 Channel Catfish in the Tallapoosa River basin: Implications for management in regulated systems

We assessed the effects of hydrology on growth and hatching success of age‐0 Channel Catfish Ictalurus punctatus in regulated and unregulated reaches of the Tallapoosa River basin, Alabama. Age‐0 Channel Catfish ( N = 91) were collected from sites in both the Coastal Plain and Piedmont regions in fall 2003 and fall 2005. Lapillus otoliths were used to estimate the daily ages of age‐0 Channel Catfish, for which hatch dates were back‐calculated. We performed growth analysis to determine growth histories of each fish at 20‐d increments from hatch. Across the 2 years of sampling, Channel Catfish hatches were documented from June 7 to September 15. Ages and growth rates of age‐0 Channel Catfish ranged from 20 to 126 d and 0.60 to 1.5 mm/d, respectively. In general, growth was highest among age‐0 Channel Catfish from unregulated sites in the lower Coastal Plain, lowest among fish from unregulated sites in the Piedmont, and intermediate from regulated sites in the Piedmont. Successful hatching typically occurred during periods when mean discharges were in the upper two quartiles of flows for each site but not during exceptionally high peaks in flow. Physiographic province, the frequency of high pulses, and the number of flow reversals were the most important factors influencing the growth of recently hatched Channel Catfish. Results suggest that a low to moderate frequency of high pulses (25–150 pulses per 20‐d increment) and a moderate number of flow reversals (~100–175 reversals per 20‐d increment) enhances early growth of Channel Catfish in the Tallapoosa River system. Managing flow, when possible, to minimize large releases of water that result in exceptionally high pulses and providing minimal hydropeaking may improve hatching success during the Channel Catfish spawning season.

Alabama↗

USGS2022

Critical thermal maximum of stream fishes including distinct populations of Smallmouth Bass

Understanding the thermal tolerances of stream fishes, including sport fishes, is important for assessing thermal stressors that are common across the landscape. Our study objectives were to determine the thermal tolerances of 17 stream fishes (15 species and 2 genetically distinct populations of juvenile Smallmouth Bass Micropterus dolomieu : the Neosho subspecies M. dolomieu velox and the Ouachita strain M . sp. cf. dolomieu velox ). Fish were collected from the field and acclimated to laboratory conditions at 20°C or 25°C, with dissolved oxygen maintained above 6 mg/L. We determined the critical thermal maximum (CTM) using an incomplete block design with 9–11 replications for each species. During trials, we increased the water temperature at a rate of 2°C per hour until fish experienced loss of equilibrium. The estimated CTM ranged from 32.43°C to 38.26°C among species. The CTM values differed significantly between taxonomic groups and species, including the genetically distinct populations of Smallmouth Bass. The Neosho subspecies of Smallmouth Bass had a significantly lower thermal tolerance than the Ouachita strain at both acclimation temperatures; however, the magnitude of the difference was about 0.5°C greater at the higher acclimation temperature. Closely related species, including the Bigeye Shiner Notropis boops and Kiamichi Shiner N . ortenburgeri , had significantly different thermal tolerances despite occupying similar riverine locations. Our results suggest that our perceptions of a species’ thermal tolerance based on that of closely related species or that of species using similar habitat may be incorrect. Moreover, the differences in thermal tolerances among populations may be an important consideration for conservation and management actions, such as stocking decisions. Laboratory data such as those provided in this study can be integrated with field data to better assess thermal responses of fishes in a changing environment.

Oklahoma↗

USGS2015

Reservoir area of influence and implications for fisheries management

Understanding the spatial area that a reservoir draws anglers from, defined as the reservoir's area of influence, and the potential overlap of that area of influence between reservoirs is important for fishery managers. Our objective was to define the area of influence for reservoirs of the Salt Valley regional fishery in southeastern Nebraska using kernel density estimation. We used angler survey data obtained from in-person interviews at 17 reservoirs during 2009–2012. The area of influence, defined by the 95% kernel density, for reservoirs within the Salt Valley regional fishery varied, indicating that anglers use reservoirs differently across the regional fishery. Areas of influence reveal angler preferences in a regional context, indicating preferred reservoirs with a greater area of influence. Further, differences in areas of influences across time and among reservoirs can be used as an assessment following management changes on an individual reservoir or within a regional fishery. Kernel density estimation provided a clear method for creating spatial maps of areas of influence and provided a two-dimensional view of angler travel, as opposed to the traditional mean travel distance assessment.

Nebraska↗

USGS2020

Application of genetic stock identification and parentage-based tagging in a mixed-stock recreational chinook salmon fishery

Genetic methods can guide and improve the management of recreational mixed-stock fisheries by informing stock-specific estimates of harvest. We applied genetic stock identification and parentage-based tagging to a recreational Chinook Salmon Oncorhynchus tshawytscha fishery in the Columbia River to illustrate the value of genetic analysis in management. We sampled landed catch in 2017 and 2018, assigned the fish to genetic reporting groups, explored temporal trends in harvest composition within and between seasons, and assessed the accuracy and precision of genetic methods against estimates from conventional tagging methodology. The genetic stock identification and parentage-based tagging produced concordant stock assignments, and the harvest composition estimates were validated with independent data. High assignment rates, relative to expended sampling effort, and precise harvest composition estimates with adequate sample sizes demonstrate that both genetic methods can be complementary, effective tools in advancing harvest assessment and recreational fisheries management. The success of genetic stock identification and parentage-based tagging supports the expanded application of genetics to similar fisheries, potentially alongside existing or emerging assessment methods, and guides future improvements in data collection and analysis.

Oregon, Washington↗

USGS2025

Estimating mortality of Lake Sturgeon in the Lake Winnebago system using traditional age-based approaches and capture–recapture models

Objective The Lake Winnebago system in Wisconsin supports a popular winter spear fishery for Lake Sturgeon Acipenser fulvescens . Setting harvest caps for this fishery relies on estimating instantaneous natural mortality rate ( M ), which can be done using age-based approaches or capture–recapture models that incorporate recoveries of fish with passive integrated transponder (PIT) tags or detections of fish with acoustic transmitters. Our objectives were to determine (1) if recent estimates of exploitation ( u ) have exceeded the 5% harvest cap, (2) if M and total mortality rates are similar among estimation methods that rely on age estimates or capture–recapture methods, and (3) if potential differences in mortality estimates would affect harvest caps. Methods Harvest of PIT-tagged fish was used to evaluate u from 2010 to 2019. Catch curves incorporating corrected fin ray ages were used to estimate total mortality and M for fish collected from 2010 to 2019. Capture–recapture models were used to estimate annual survival and M from detections of fish with acoustic transmitters from 2007 to 2019 and recoveries of PIT-tagged fish from 1999 to 2020. Mortality estimates were used to calculate and compare sex-specific harvest caps among estimation methods. Results Observed u did not exceed 5% for either sex between 2010 and 2019. Estimates of M varied among methods (males: M = 0.001–0.134; females: M = 0.001–0.131), with PIT-based models consistently providing the lowest and telemetry-based models providing the highest estimates. Simulations indicated that female u has limited potential to exceed 5% if M from fin ray ages or telemetry is used to set harvest caps, while PIT-based simulations showed no indication of cap exceedance. Conclusions Harvest management practices in the Lake Winnebago system appear to have kept Lake Sturgeon exploitation below the 5% harvest cap from 2010 to 2019. Capture–recapture models relying on PIT tags appear to provide the most precise approach for setting harvest caps for this fishery.

Wisconsin↗

USGS2019

Coldwater periods in warmwater streams: Microhabitat shifts from autumn to winter by Smallmouth Bass

Seasonal and life stage variation in microhabitat use is an important driver of fish survival and bioenergetics, but knowledge of microhabitat selection during colder periods is generally lacking in warmwater streams. Our objective was to examine changes in microhabitat selection by age‐0 (TL ≤ 85 mm) and age‐1+ (TL > 85 mm) Smallmouth Bass Micropterus dolomieu from autumn to winter in streams of the southwest Ozark Highlands ecoregion. We examined microhabitat selection (depth, velocity, substrate, cover, and temperature) during autumn 2017 (Spavinaw Creek) and winter 2018 (Spavinaw and Spring creeks). During autumn and winter, age‐0 fish selected intermediate depths of approximately 1 m, whereas age‐1+ fish selected the deepest available habitat. Water depth selection was similar across seasons for both life stages. Both age‐0 and age‐1+ bass selected areas of zero velocity, increasing substrate size, instream cover, and warmwater patches in autumn. Velocity selection differed between autumn and winter with both life stages showing stronger selection of low velocity patches (0.1–0.3 m/s) during winter. Both life stages shifted to having no substrate selection during winter. Age‐1+ bass were more likely than age‐0 bass to use cover during autumn, but this relationship shifted in winter to the age‐0 cohort increasing their selection of cover and the age‐1+ cohort decreasing their selection. Both age‐0 and age‐1+ bass selected relatively warmer habitats during autumn, but not winter. Collectively, our results highlight both seasonal and life stage variation in Smallmouth Bass microhabitat selection. As our understanding of habitat selection across seasons develops, the management of Smallmouth Bass will undoubtedly improve. Changing environmental conditions over time may influence available habitat as well as the timing of seasonal shifts across a range of spatial and temporal scales, including microhabitat patches.

Arkansas, Oklahoma↗

USGS2016

Impacts of Northern Pike on stocked Rainbow Trout in Pactola Reservoir, South Dakota

Establishment of nonnative Northern Pike Esox lucius in Pactola Reservoir, South Dakota, has prompted concern among biologists about the influence of this species on the lake’s intensively managed salmonid fisheries. Ancedotal information suggests that catch rates of Rainbow Trout Oncorhynchus mykiss have declined while mean size and abundance of Northern Pike has increased, although quantitative information on diet and growth of the Northern Pike population is lacking. To address potential interactions between Northern Pike and Rainbow Trout, we assessed size-dependent predation by Northern Pike on Rainbow Trout and determined the relative energetic contribution of stocked Rainbow Trout to Northern Pike growth using bioenergetics modeling. Stable isotopes combined with traditional diet analyses revealed that smaller Northern Pike (<600 mm TL) consumed primarily centrarchids and Rainbow Smelt Osmerus mordax , and Rainbow Trout contributed less than 10% to their annual energy consumption. In contrast, larger Northern Pike (≥600 mm TL) consumed primarily Rainbow Trout, which accounted for 56% of their annual energy consumption. Combining estimates of Northern Pike predation with production costs of catchable-size Rainbow Trout revealed that annual economic losses ranged from US$15,259 to $24,801 per year. Over its lifespan, an age-10 Northern Pike was estimated to consume ~117 Rainbow Trout worth approximately $340. Thus, Northern Pike predation substantially influences salmonid management initiatives and is likely a primary factor contributing to reduced Rainbow Trout abundance and return to anglers in Pactola Reservoir. Strategies for reducing Northern Pike predation on Rainbow Trout include increasing the size of stocked fish or altering the timing and spatial distribution of stocking events.

South Dakota↗

USGS2019

Evaluation of artificial cover units as a sampling technique and habitat enhancement for madtoms in rivers

Instream habitat degradation and loss are major threats to freshwater fishes and critical conservation issues among nongame species, due to a lack of research and knowledge concerning their habitat requirements. Instream physical cover is an important component of fish habitat, especially for benthic species that require cover for reproduction and shelter from predators. One such species is the Carolina Madtom Noturus furiosus, a small, imperiled, nongame catfish endemic to the Neuse and Tar river basins of North Carolina. To enhance understanding of instream cover dynamics, we constructed artificial cover units from terra cotta materials and deployed them in rivers to (1) evaluate if they could be an effective passive sampling technique to estimate detection and occupancy of the Carolina Madtom, and (2) determine their potential to enhance habitat in systems where instream cover has been lost. Artificial cover units were deployed at 8 sites in the Neuse and Tar river basins, and collected 30 Carolina Madtoms at 2 sites in the Tar River basin. Occupancy modeling estimated Carolina Madtom detection probability using artificial cover units at 0.92. Compared to other standardized sampling methods, artificial cover units were an efficient, passive sampling technique for detecting Carolina Madtoms. Observations also revealed that artificial cover units were occupied by Carolina Madtoms for reproduction. These findings provide natural resource managers an additional means to assess the status of this imperiled species using an inexpensive, passive sampling device that can provide spawning habitat, protection from predators, and help mitigate effects of instream habitat degradation.

North Carolina↗

USGS2020

Use of underwater videography to quantify conditions utilized by endangered Moapa Dace While spawning

Advances in underwater camera technology provide an affordable means to quantify the environmental conditions under which fish spawn. This information is important for investigating spawning ecology, managing habitat, or providing information for captive breeding programs. We deployed 12 modified security cameras underwater to identify environmental conditions related to the spawning behavior of the critically endangered Moapa Dace Moapa coriacea , a Mojave Desert stream-dwelling cyprinid that had never been observed spawning and that had fallen to a low of 459 individual fish 4 years prior to this study. Camera sites were selected systematically along the stream to represent the variety of conditions available. We divided the field of view in front of each camera into a grid, and we estimated both the available environment and the habitat over which Moapa Dace showed spawning behavior. From over 4,000 10-min video clips that were randomly selected for analysis, 13 spawning events were identified. Using nonparametric contingency table analyses, we found that Moapa Dace selected depths between 30 and 34 cm, water velocities between 0.11 and 0.17 m/s, cobble substrate, and overhead instream cover. Although the recorded sample size of spawning events was small (13), our sample represents a large proportion of events given that the world's entire population of Moapa Dace at the time was approximately 650 fish distributed over multiple kilometers of stream length. Environmental conditions identified by this study were replicated in laboratory facilities to successfully propagate Moapa Dace for the first time in captivity. These propagation methods are now used in a management setting by the Nevada Department of Wildlife to maintain a captive population of this rare fish. Camera methods can be effective in helping to identify spawning conditions where water clarity is sufficient.

Nevada↗

USGS2023

Why are larger fish farther upstream? Testing multiple hypotheses using Silver Chub in two Midwestern United States riverscapes

Objective Three competing hypotheses might explain the widely documented intrapopulation larger-fish-upstream phenomenon. The age-phased recruitment hypothesis posits that fish spawn downstream and move upstream as they age and grow, the static population with growth and mortality gradients hypothesis posits that fish spawn throughout a riverscape and growth is greater upstream while recruitment is greater downstream, and the colonization cycle hypothesis posits that fish spawn upstream, larvae drift downstream, and individuals move upstream as they age and grow. Methods We tested for the larger-fish-upstream pattern using populations of Silver Chub Macrhybopsis storeriana in the Arkansas and Ohio rivers, as well as investigated longitudinal variation in reproductive investment (Arkansas River), age structure for adult fish (Arkansas River), and number and occurrence of age-0 fish (Ohio River). Result The larger-fish-upstream pattern was temporally persistent in both riverscapes. In the Arkansas River, reproductive investment was greatest upstream, where initiation of spawning likely occurred based on gonadosomatic indices. Adult fish were most numerous in the Arkansas River 125–175 km upstream from Kaw Reservoir, with age-2 fish numbers peaking farther upstream compared with age-1 fish. In the Ohio River, age-0 fish counts increased downstream and were rare among the shortest river fragments (<100 km) between lock-and-dam structures. These findings are inconsistent with the age-phased recruitment hypothesis based on upstream spawning in the Arkansas River and inconsistent with the static population with growth and mortality gradients hypothesis based on virtual absence of age-2 fish downstream (Arkansas River) and age-0 fish upstream (Ohio River). The most likely explanation for longitudinal variation in Silver Chub size distribution is downstream drift of ichthyoplankton followed by net upstream movement (i.e., colonization cycle hypothesis), but formal assessments of movement and ova characteristics require more research. Conclusion Managing multidimensional riverscapes requires insight into the mechanisms that regulate upstream-to-downstream patterns in fish populations, and our work underscores a potential size-related benefit to maintaining broadscale longitudinal connectivity.

Arkansas River, Ohio River↗

USGS2015

Muskellunge growth potential in northern Wisconsin: implications for trophy management

The growth potential of Muskellunge Esox masquinongy was evaluated by back-calculating growth histories from cleithra removed from 305 fish collected during 1995–2011 to determine whether it was consistent with trophy management goals in northern Wisconsin. Female Muskellunge had a larger mean asymptotic length (49.8 in) than did males (43.4 in). Minimum ultimate size of female Muskellunge (45.0 in) equaled the 45.0-in minimum length limit, but was less than the 50.0-in minimum length limit used on Wisconsin's trophy waters, while the minimum ultimate size of male Muskellunge (34.0 in) was less than the statewide minimum length limit. Minimum reproductive sizes for both sexes were less than Wisconsin's trophy minimum length limits. Mean growth potential of female Muskellunge in northern Wisconsin appears to be sufficient for meeting trophy management objectives and angler expectations. Muskellunge in northern Wisconsin had similar growth potential to those in Ontario populations, but lower growth potential than Minnesota's populations, perhaps because of genetic and environmental differences.

Wisconsin↗

USGS2000

Evaluation of a 16-inch minimum length limit for smallmouth bass in Pallette Lake, Wisconsin

We evaluated a 16-in minimum length limit and two-fish daily bag limit for smallmouth bass Micropterus dolomieu in Pallette Lake, Wisconsin, from 1989 to 1996. Fish abundance, biomass, growth, survival, and angler harvest were compared with data from years when no length or bag limits were in force. Angler harvest and fishing effort were monitored by a complete mandatory creel census. Following the regulation changes, fishing effort increased by 62% despite a 95% decline in smallmouth bass harvest. The number and biomass of smallmouth bass 12.0-15.9 in and 16.0 in and greater increased, whereas the number of fish 6.0-11.9 in declined. Annual survival rates of fish age 3 and older increased from 0.21 during the no-limit years to 0.60 during the length-limit years. Annual exploitation rates for fish 8 in and greater averaged 0.53 during the no-limit years and 0.10 during the length-limit years. Smallmouth bass growth rates did not change. During the no-limit years, 27% of the anglers harvested smallmouth bass compared with only 3% of anglers during the length-limit years. The bag limit reduced harvest during only 3 years by an average of 11% (3 fish/year). Anglers accepted the restrictive regulations well and were primarily concerned about catch rates of fish 16.0 in and greater. For managers wishing to increase angler interest and numbers of fish 16.0 in and greater, we recommend considering similar or even more restrictive regulations. However, a sharp reduction in the number of smallmouth bass above the minimum length limit should be expected.

Wisconsin↗

USGS2014

Quantifying the effectiveness of conservation measures to control the spread of anthropogenic hybridization in stream salmonids: A climate adaptation case study

Quantifying the effectiveness of management actions to mitigate the effects of changing climatic conditions (i.e., climate adaptation) can be difficult, yet critical for conservation. We used population genetic data from 1984 to 2011 to assess the degree to which ambient climatic conditions and targeted suppression of sources of nonnative Rainbow Trout Oncorhynchus mykiss have influenced the spread of introgressive hybridization in native populations of Westslope Cutthroat Trout O. clarkii lewisi . We found rapid expansion in the spatial distribution and proportion of nonnative genetic admixture in hybridized populations from 1984 to 2004, but minimal change since 2004. The spread of hybridization was negatively correlated with the number of streamflow events in May that exceeded the 75th percentile of historic flows ( r = −0.98) and positively correlated with August stream temperatures ( r = 0.89). Concomitantly, suppression data showed a 60% decline in catch per unit effort for fish with a high proportion of Rainbow Trout admixture, rendering some uncertainty as to the relative strength of factors controlling the spread of hybridization. Our results illustrate the importance of initiating management actions to mitigate the potential effects of climate change, even where data describing the effectiveness of such actions are initially limited but the risks are severe.

Montana↗

USGS2018

Genetic population structure of Shoal Bass within their native range

Endemic to the Apalachicola River basin of the southeastern USA, the Shoal Bass Micropterus cataractae is a fluvial‐specialist sport fish that is imperiled because of anthropogenic habitat alteration. To counter population declines, restorative stocking efforts are becoming an increasingly relevant management strategy. However, population genetic structure within the species is currently unknown, but it could influence management decisions, such as brood source location. Leveraging a collaborative effort to collect and genotype specimens with 16 microsatellite loci, our objective was to characterize hierarchical population structure and genetic differentiation of the Shoal Bass across its native range, including an examination of structuring mechanisms, such as relatedness and inbreeding levels. Specimens identified as Shoal Bass were collected from 13 distinct sites ( N ranged from 17 to 209 per location) and were then taxonomically screened to remove nonnative congeners and hybrids (pure Shoal Bass N ranged from 13 to 183 per location). Our results revealed appreciable population structure, with five distinct Shoal Bass populations identifiable at the uppermost hierarchical level that generally corresponded with natural geographic features and anthropogenic barriers. Substructure was recovered within several of these populations, wherein differences appeared related to spatial isolation and local population dynamics. An analysis of molecular variance revealed that 3.6% of the variation in our data set was accounted for among three larger river drainages, but substructure within each river drainage also explained an additional 8.9% of genetic variation, demonstrating that management at a scale lower than the river drainage level would likely best conserve genetic diversity. Results provide a population genetic framework that can inform future management decisions, such as brood source location, so that genetic diversity within and among populations is conserved and overall adaptability of the species is maintained.

Apalachicola–Chattahoochee–Flint River Basin↗

USGS2021

Recruitment bottlenecks for age-0 walleye in northern Wisconsin lakes

Some northern Wisconsin lakes have shown declines in catches of age-0 Walleye Sander vitreus in standardized fall electrofishing sampling, suggesting that recruitment bottlenecks are occurring in the first several months of life. In 2016 and 2017, we sampled six lakes with declining trends in natural Walleye recruitment (D-NR lakes) and seven lakes with a history of sustained natural recruitment (S-NR lakes) to determine if timing of potential recruitment bottlenecks for age-0 Walleye were consistent among D-NR lakes and if abiotic and biotic metrics differed between D-NR and S-NR lakes. We also examined diets of larval Walleye to assess prey items that may be important to early growth and survival and to determine if occurrence of piscivory was related to larval Walleye total length. Differential patterns in the presence and absence of age-0 Walleye at different life history stages in the first 6 months of life suggested that recruitment bottlenecks in D-NR lakes were consistently occurring before mid-July (five of six lakes). Mean Secchi depth, surface conductivity, abundance of larval Yellow Perch Perca flavescens , and most metrics of zooplankton abundance and mean size were similar between D-NR and S-NR lakes. Log 10 transformed number of adult Walleye per hectare was lower and adult mean total length was higher in D-NR lakes. Across all lakes, diets of larval Walleye consisted of zooplankton and larval fish and the occurrence of piscivory was higher than reported in previous studies and was positively related to total length of larval Walleye. Causes of recruitment bottlenecks in D-NR lakes remain unclear, making it difficult to identify management actions that might be implemented to circumvent these bottlenecks. However, our results indicate that future research should focus on the period between egg deposition and mid-July.

Wisconsin↗