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At least 145 records · Page 8Linked to original sources
USGS2020

Comparison of underwater video with electrofishing and dive‐counts for stream fish abundance estimation

Advances in video technology enable new strategies for stream fish research. We compared juvenile (age‐0) and adult (age 1+) Brook Trout Salvelinus fontinalis abundance estimates from underwater video with backpack electrofishing and dive‐count methods across a series of stream pools in Shenandoah National Park, Virginia ( n = 41). Video methods estimated greater mean abundance of adult trout than 1‐pass electrofishing but were not different than 3‐pass electrofishing or dive‐count methods in this regard. In contrast, videos underestimated abundance of juvenile trout, and we suggest this is because predator avoidance‐behaviors by juvenile trout limit their use of microhabitat locations visible to cameras. Integrated abundance estimates from 2 cameras increased correspondence to comparison methods relative to single cameras, demonstrating the importance of an expanded field of view for video sampling in streams. Geomorphic features helped explain method‐wise differences: more adult trout were estimated with video than 3‐pass electrofishing as riffle crest depth and boulder composition increased, indicating habitat associations with trout escapement from electrofishing. Our results demonstrated that video techniques can provide a robust alternative or supplement to traditional methods for estimating adult trout abundance in stream pools.

Virgiinia↗
USGS2020

Groundwater upwelling regulates thermal hydrodynamics and salmonid movements during high-temperature events at a montane tributary confluence

The Smith River is a popular recreational sport fishery in western Montana, but salmonid abundances there are thought to be artificially limited by riparian land-use alterations, irrigation water withdrawals, and high summer water temperatures. We used integrated networks of temperature loggers, PIT tag antenna stations, and in situ temperature mapping to investigate the thermal hydrodynamics and associated movements of PIT-tagged salmonids at the confluence of Tenderfoot Creek, a major, unaltered coldwater tributary of the Smith River. Contrary to expectations, Tenderfoot Creek itself was not used as a thermal refuge by salmonids during periods of high water temperatures in Smith River; rather, its cool outflow plume into the main stem was used instead. Mean daily outflow water temperatures averaged 2.9°C lower than those of the Smith River during summer and ranged from 0.5°C to 6.1°C lower. Moreover, measured and estimated temperatures in the outflow were cooler (by up to 2.8°C) than in Tenderfoot Creek itself at times as a result of groundwater upwelling at the confluence. Detections of PIT-tagged fish in the thermal plume increased, especially at night, when daily mean water temperatures exceeded 20°C in the main-stem Smith River; more than four times as many PIT-tagged fish were detected in the plume ( N = 52) than along the opposite bank ( N = 12), which ostensibly afforded better cover. Coldwater tributary confluences may provide superior thermal refuges for salmonids—cooler than the tributaries themselves—when water temperatures in river main stems are stressful.

Montana↗
USGS2020

Evaluation of genetic structuring within GIS‐derived Brook Trout management units

Delineation of management units across broad spatial scales can help to visualize population structuring and identify conservation opportunities. Geographical information system (GIS) approaches can be useful for developing broad‐scale management units, especially when paired with field data that can validate the GIS‐based delineations. Genetic data can be useful for evaluating whether management units accurately represent population structuring. The Eastern Brook Trout Joint Venture, a regionwide collaborative group, delineated patch‐based management units for Brook Trout Salvelinus fontinalis by using GIS approaches to inform conservation strategies across the eastern United States. The objectives of this research were to (1) evaluate how well the patches predicted Brook Trout genetic structuring in Connecticut, USA; (2) modify the patches as needed to represent contemporary genetic structuring; and (3) identify catchment‐ and patch‐scale riverscape characteristics that predict genetic diversity. Patches with dams and high levels of upstream impervious surfaces (>3%) had increased intrapatch genetic structuring, which we incorporated into our revised patch delineation algorithm. Patch area and catchment area were the best predictors of genetic diversity, suggesting the importance of maintaining connectivity and incorporating patch‐scale processes into conservation actions. The modified patch layer could be used as the basis for Brook Trout management units to help predict population structuring in the absence of watershed‐scale genetic data, allowing opportunities for Brook Trout conservation to be identified.

Connecticut↗
USGS2020

Evaluation of visible light as a cue for guiding downstream migrant juvenile Sea Lamprey

Light can modify orientation and locomotory behaviors in fish and has been applied to attract or repel migrant fish by inducing positive or negative phototaxis. Here, recently metamorphosed downstream‐migrating Sea Lamprey Petromyzon marinus were exposed to light cues in several orientations and intensities at night under controlled flowing‐water conditions in a laboratory flume. Behaviors and rates of downstream movement were monitored with overhead cameras and nets. When exposed to low‐intensity white light, 16–23% more Sea Lamprey were captured in a net closest to the light cue array compared to a dark control condition, suggesting some degree of positive phototaxis at low light levels (100 lx at a distance of 1 m from the light source). An interaction with the side of the flume (possibly due to varying flow conditions) and light treatment was also observed. At higher light intensities (1,000 lx at 1 m from the source), Sea Lamprey progressed downstream at a lower rate than was observed during dark conditions. After high‐intensity light treatments, fewer Sea Lamprey were observed in the nets at the downstream end of the flume and more Sea Lamprey were observed in the flume or in the release channel compared to dark control trials. Therefore, some photonegative behavior may be expressed at light levels of 1,000 lx or greater, perhaps as an attempt to avoid detection by predators by remaining stationary or seeking shelter. Light may have utility as a cue used for guidance devices to control Sea Lamprey, but further research is needed to define how light intensity and the environment (turbidity, depth, water velocity, and natural habitat features) influence locomotion, changes in swimming depth, and other behavioral responses of downstream‐migrating juvenile Sea Lamprey.

Transactions of the American Fisheries Society↗
USGS2021

Juvenile Chinook salmon survival, travel time, and floodplain use relative to riverine channels in the Sacramento–San Joaquin River Delta

Floodplains provide multiple benefits to both resident and migratory fish species, including juvenile Chinook Salmon Oncorhynchus tshawytscha , but direct comparisons of survival during migration through a floodplain versus riverine routes are scarce. The Yolo Bypass is a broad floodplain of the Sacramento River that floods in about 30% of years in response to large, uncontrolled runoff events. We analyzed data from an acoustic telemetry study conducted in winter 2016 to estimate the proportion of tagged juvenile Chinook Salmon entrained from the Sacramento River into the Yolo Bypass and their spatial distribution within the Yolo Bypass. In addition, we compared survival and travel time of Chinook Salmon that migrated through the Yolo Bypass to those migrating via alternative non‐floodplain migration routes at varying stages of a flood event that activated the Yolo Bypass. We found that entrainment into the Yolo Bypass ranged from 1% to 80% among different release groups, with the highest entrainment coinciding with the peak of the March 2016 flooding event. Survival for Chinook Salmon migrating through the Yolo Bypass was similar to survival of those migrating through main‐stem migration routes. At the relatively high flows necessary to enable flooding of the Yolo Bypass, survival estimates varied little among release groups and migration routes. Furthermore, mean daily survival rates for Chinook Salmon migrating through the flooded Yolo Bypass were comparable to those of fish migrating through the other non‐floodplain routes. Median travel times remained relatively constant during various stages of flooding in the Yolo Bypass. This research should help managers to better understand the potential costs and benefits to floodplain restoration and routing of migrating Chinook Salmon into off‐channel habitat.

California↗
USGS2021

Feeling the squeeze: Adult run size and habitat availability limit juvenile river herring densities in lakes

Maximum densities of juvenile river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis ) vary among freshwater lakes, likely due to densities of adult spawners. Differences in habitat availability and lake water quality may also contribute to variation in juvenile river herring productivity between populations, yet these relationships have not been tested across a large geographic scope. In this study we investigated relationships between juvenile river herring densities and (1) spawning adult river herring densities, (2) lake habitat availability, and (3) lake water quality in 29 freshwater lakes in the northeastern USA. Purse seines were used at night to sample juvenile river herring monthly in June–August 2014 and 2015, with concurrent collection of lake-specific physical (e.g., lake surface area, mean depth, depth to thermocline), chemical (e.g., nitrogen, phosphorus, dissolved organic carbon [DOC]), and biological (chlorophyll a , adult spawning density) data. Spawning adult density (number of adults per surface area of lake) explained 66.6% of the variation in juvenile densities using a generalized additive model. Juvenile densities increased with increasing adult density, peaking at roughly 1,000 adults/ha, and then declined at higher adult densities, suggesting a limit to carrying capacity in juvenile production. Linear mixed-effects models revealed that differences in water quality and habitat across lakes explained additional variation in juvenile densities. Specifically, DOC was negatively related to juvenile densities, suggesting that DOC limits the amount of suitable, well-oxygenated epilimnion habitat available to juvenile river herring in late summer. Our results can be used to help understand expected juvenile production based on adult density within a lake, to inform expectations about juvenile growth and survival, and to understand the mechanisms for how changes in habitat availability and water quality affect river herring populations.

Connecticut, Maine, Massachusetts, New Hampshire, ↗
USGS2021

Identifying information gaps in predicting winter foraging habitat for juvenile Gulf Sturgeon

The Gulf Sturgeon Acipenser oxyrinchus desotoi is an anadromous species that inhabits Gulf of Mexico coastal waters from Louisiana to Florida and is listed as threatened under the U.S. Endangered Species Act. Seasonal cues (e.g., freshwater discharge) determine the timing of spawning and migration and may influence the availability of critical habitat during winter months in six estuaries. Large information gaps, especially related to critical estuarine habitat for juveniles, hinder recovery efforts to protect these habitats and assess risks from emerging threats. Using Apalachicola Bay, Florida, as a model system, we developed and analyzed a preliminary Bayesian network model so that we could identify knowledge gaps (i.e., where expert knowledge was lacking) and data gaps (i.e., where data were unavailable) that limit the ability to assess the quantity of critical estuarine habitat for juvenile Gulf Sturgeon. The model hypothesized habitat availability per winter month in estuarine habitat under alternative scenarios of river discharge and length of the winter foraging season. A search for geospatial data sets revealed that the largest gap involved salinity, temperature, and oxygen (i.e., water condition) monitoring data, with data available only for Apalachicola Bay. For the Apalachicola Bay model, data gaps prevented the development of 53% of water condition geospatial data sets and a sensitivity analysis showed that water condition data most limited the ability to predict habitat availability. Expert knowledge was low, and conditional certainty scores showed that the relationships with the lowest certainty were abiotic suitability and habitat availability. Reducing information gaps could aid the development of a model that is appropriate for informing management. Future efforts could prioritize the expansion of water monitoring within critical habitat estuaries and predicting abiotic suitability and habitat availability. Bayesian network models can easily incorporate prior and new information for complex systems. Thus, our model could be updated as future research and monitoring efforts close these information gaps.

Florida↗
USGS2021

Movement, survival, and delays of Atlantic Salmon smolts in the Piscataquis River, Maine, USA

Movement, delays, and survival of hatchery Atlantic Salmon Salmo salar smolts were evaluated through the Piscataquis River, a tributary of the Penobscot River in Maine, USA. We explored the effects of the river’s four dams (Guilford, Dover, Browns Mill, and Howland dams) from 2005 to 2019. During this period, the downstream-most dam (Howland Dam) transitioned from full hydropower generation to seasonal turbine shutdowns and later was decommissioned with the construction of a nature-like fish bypass in 2016. We estimated survival through open-river reaches and at each dam using acoustic telemetry ( n = 1,611). Dams decreased survival, with per-river-kilometer (rkm) apparent survival averages of 0.972, 0.951, and 0.990 for Guilford, Dover, and Browns Mill dams compared to a per-rkm survival of 0.999 for open-river reaches. Turbine shutdowns increased survival at Howland Dam (to around 0.95), which was further increased by the nature-like fish bypass (0.99). We used radiotelemetry in 2019 ( n = 75) and demonstrated that approximately one-third of the fish used the bypass, while the remaining fish used alternative routes. Smolts successfully passing the three upstream dams had lower apparent survival through Howland Dam than smolts that were released upstream of Howland Dam. Although smolts passing Browns Mill Dam had high survival, the dam caused extended delays, with median delay times surpassing 48 h in most years. Most of the delays caused by Browns Mill Dam occurred after fish had passed the dam and may indicate a sublethal effect of passage. Overall, while survival through Howland Dam has improved, passage and delays at the three upstream dams in aggregate represent a critical impediment to the effective use of the high-quality spawning habitat found upstream.

Maine↗
USGS2021

Eastward expansion of Round Goby in New York: Assessment of detection methods and current range

The Round Goby Neogobius melanostomus has spread rapidly around the Great Lakes region since its introduction to North America in 1990. In 2014, a specimen was captured in the New York State Canal System west of Utica, prompting concerns that Round Goby would soon reach the ecologically and economically valuable watersheds of Lake Champlain and the Hudson River estuary. The establishment of Round Goby populations elsewhere has been linked to a number of negative ecological consequences, yet methods for monitoring the invasion front of this species remain limited. The objectives of this study were to assess the current distribution of Round Goby in central New York and to determine the most effective methods for monitoring the invasion front. This was achieved by concurrently using benthic trawling, seining, minnow traps, and environmental DNA (eDNA) twice annually from 2016 to 2019 at 12 sites on the canal system between Oneida Lake and the Hudson River. Of the three traditional gear types, benthic trawling was the most effective method and captured Round Goby as far east as Utica by 2019. This finding suggests only minimal eastward expansion of Round Goby occurred between 2014 and 2019. Round Goby DNA was detected in water samples during all surveys in which individuals were captured with trawling, and the estimated concentration of DNA explained 69% of the variability in trawl catch. At multiple study sites, Round Goby DNA was identified during consecutive surveys before Round Goby were first captured with trawling. This suggests that in lotic waters, eDNA has the potential to forecast or serve as a sentinel for the expansion of Round Goby to new locations. Our results demonstrate the importance of using eDNA in a repeated sampling framework and supplementing eDNA sampling with some level of effort with traditional sampling methods.

Great Lakes↗
USGS2021

Exploring the contemporary relationship between predator and prey in a significant, reintroduced Lahontan Cutthroat Trout population

Lahontan Cutthroat Trout (LCT) Oncorhynchus clarkii henshawi have experienced some of the most marked reductions in abundance and distribution among Cutthroat Trout subspecies. The population of LCT in Pyramid Lake, Nevada has returned from the brink of extirpation, and although it is highly managed via stocking, the population is thriving and has recently started to reproduce naturally. Our objectives were to determine (1) whether predator and prey remain tightly coupled, (2) whether LCT are food limited, and (3) the status of the LCT population with regard to the potential prey-based contemporary carrying capacity. We used a multifaceted approach, including intensive field sampling of fish, bioenergetics modeling, cohort reconstruction, and comparisons of prey availability to consumption. We estimated that the average population of LCT in Pyramid Lake is 1.2 million, average annual stocking is 650,000, and the number of fish angled ranges from 5,000 to 14,000 per year, with a 90% release rate. Driven by seasonal and size variation in consumption, individual annual consumption by LCT varied from 667 to 992 g/year for small LCT (200–400 mm TL) and from 2,388 to 3,057 g/year for large LCT (>400 mm TL). Lahontan Cutthroat Trout are consuming, on average, 14–63% of the standing crop of Tui Chub Siphateles bicolor annually, indicating that LCT are currently not exceeding their prey-based carrying capacity. The LCT in Pyramid Lake remain tightly coupled to their primary native prey, Tui Chub, despite considerable changes to the ecosystem; therefore, managing for a robust population of LCT translates largely to managing for forage fish. This supply-versus-demand issue is of particular concern for Pyramid Lake given that the density of Tui Chub may be declining concordant with declining lake elevation. Given the conservation importance of this LCT population, careful monitoring is critical; however, “predation inertia” indicates that effective short-term management in response to fluctuations in forage fishes is likely possible.

Nevada↗
USGS2021

Climate change may cause shifts in growth and instantaneous natural mortality of American Shad throughout their native range

American Shad Alosa sapidissima is an anadromous species with populations ranging along the U.S. Atlantic coast. Past American Shad stock assessments have been data limited and estimating system-specific growth parameters or instantaneous natural mortality ( M ) was not possible. This precluded system-specific stock assessment and management due to reliance on these parameters for estimating other population dynamics (such as yield per recruit). Furthermore, climate-informed biological reference points remain a largely unaddressed need in American Shad stock assessment. Population abundance estimates of American Shad and other species often rely heavily on M derived from von Bertalanffy growth function (VBGF) parameters. Therefore, we developed Bayesian hierarchical models to estimate coastwide, regional, and system-specific VBGF parameters and M using data collected from 1982 to 2017. We tested predictive performance of models that included effects of various climate variables on VBGF parameters within these models. System-specific models were better supported than regional or coast-wide models. Mean asymptotic length ( L ∞ ) decreased with increasing mean annual sea surface temperature (SST) and degree days (DD) experienced by fish during their lifetime. Although uncertain, K (Brody growth coefficient) decreased over the same range of lifetime SST and DD. Assuming no adaptation, we projected changes in VBGF parameters and M through 2099 using modeled SST from two climate projection scenarios (Representative Concentration Pathways 4.5 and 8.5). We predicted reduced growth under both scenarios, and M was projected to increase by about 0.10. It is unclear how reduced growth and increased mortality may influence population productivity or life history adaptation in the future, but our results may inform stock assessment models to assess those trade-offs.

Transactions of the American Fisheries Society↗
USGS2021

Estimates of food consumption rates for invasive Blue Catfish

As a prolific invasive species, Blue Catfish Ictalurus furcatus threaten native organisms in numerous estuarine and tidal freshwaters along the Atlantic coast of the United States. However, no published estimates of consumption rates are available for Blue Catfish in the scientific literature. This information is critical for development of bioenergetics models or estimation of population‐level impacts on native species. Using a combination of field and laboratory studies, we provide the first estimates of daily ration, maximum daily ration, and consumption to biomass ratios for Blue Catfish populations. Ad libitum feeding trials conducted in our laboratory reveal that maximum daily ration in Blue Catfish varies by prey type, temperature, and fish size, with maximal feeding occurring in medium‐sized Blue Catfish (500–600 mm total length) and at temperatures ≥15°C. Furthermore, estimates of daily ration were higher for fish prey (Gizzard Shad Dorosoma cepedianum ) than for crustacean prey (blue crab Callinectes sapidus ). Diel feeding chronologies based on field‐collected diet samples from 1,226 Blue Catfish demonstrated river‐specific variability in daily ration and maximum daily ration. Blue Catfish daily ration ranged between 2.27% and 5.22% bodyweight per 24 h, while maximum daily ration ranges between 8.56% and 9.37% bodyweight per 24 h. Estimates of consumption to biomass ratios varied by river and Blue Catfish size groupings but range between 2.42 and 3.39, which is similar to other benthic omnivores. This research will inform the assessment of predatory impacts of invasive Blue Catfish in the Chesapeake Bay and beyond as it will enable researchers to estimate predatory impacts through the coupling of population models, food habit information, and consumption rate information (current study).

Virginia↗
USGS2021

Daily patterns of river herring (Alosa spp.) spawning migrations: Environmental drivers and variation among coastal streams in Massachusetts

The timing of life history events in many plants and animals depends on the seasonal fluctuations of specific environmental conditions. Climate change is altering environmental regimes and disrupting natural cycles and patterns across communities. Anadromous fishes that migrate between marine and freshwater habitats to spawn are particularly sensitive to shifting environmental conditions and thus are vulnerable to the effects of climate change. However, for many anadromous fish species the specific environmental mechanisms driving migration and spawning patterns are not well understood. In this study, we investigated the upstream spawning migrations of river herring Alosa spp. in 12 coastal Massachusetts streams. By analyzing long-term data sets (8–28 years) of daily fish counts, we determined the local influence of environmental factors on daily migration patterns and compared seasonal run dynamics and environmental regimes among streams. Our results suggest that water temperature was the most consistent predictor of both daily river herring presence–absence and abundance during migration. We found inconsistent effects of streamflow and lunar phase, likely due to the anthropogenic manipulation of flow and connectivity in different systems. Geographic patterns in run dynamics and thermal regimes suggest that the more northerly runs in this region are relatively vulnerable to climate change due to migration occurring later in the spring season, at warmer water temperatures that approach thermal maxima, and during a narrower temporal window compared to southern runs. The phenology of river herring and their reliance on seasonal temperature patterns indicate that populations of these species may benefit from management practices that reduce within-stream anthropogenic water temperature manipulations and maintain coolwater thermal refugia.

Massachusetts↗
USGS2021

Habitat associations of black basses in a reservoir system

The habitat associations of three species of black bass Micropterus spp. were examined in six habitat types (i.e., sediment, gravel, rock, riprap, brush, and aquatic plants) along a cascade of 10 reservoirs in the Tennessee River. We tested whether habitat selection differed among the three species and whether species’ co-occurrence depended on habitat type. We found that some species occurred in some habitats in proportion to habitat availability (some at higher frequencies and some at frequencies lower than availability) and that juveniles and adults exhibited similar occurrence patterns. Our habitat selection results largely corroborate previous descriptions of black bass habitat associations and generally track preference for lithic habitats, as reported in native streams. We expected the different black bass species to show negative co-occurrence to avoid competitive interactions. Nevertheless, we found that with few exceptions, adults co-occurred in habitats mostly as expected by chance and juveniles co-occurred more often than was expected by chance. Our findings imply that environmental filtering, rather than competitive interactions that dominate in natural environments, may be the dominant mechanism shaping black bass assemblages in reservoirs of the Tennessee River. The observed patterns of habitat selection and co-occurrence further suggest that the conservation and management of black bass assemblages in reservoirs can be supported through habitat management activities. Protecting and enhancing the remaining lithic habitat in the reservoirs as well as recovering habitat that is blanketed by sediment could provide desirable environments for all black bass species.

Tennessee River basin↗
USGS2021

Interacting effects of density-dependent and density-independent factors on growth rates in southwestern Cutthroat Trout populations

Density-dependent (DD) and density-independent (DI) effects play an important role in shaping fish growth rates, an attribute that correlates with many life history traits in fishes. Consequently, understanding the extent to which DD and DI effects influence growth rates is valuable for fisheries assessments because it can inform managers about how populations may respond as environmental conditions continue to change (e.g., threats from climate change). We used a Rio Grande Cutthroat Trout Oncorhynchus clarkii virginalis (RGCT) capture–mark–recapture data set collected over 2 years along a temperature and density gradient in northern New Mexico streams to test the extent to which DD and DI effects interact to influence specific growth rates. We found that temperature (DI) and density (DD) interacted with RGCT life stage (i.e., immature or mature) to affect growth rates. We only detected evidence of a negative DD effect on RGCT growth for the immature fraction of a population when exposed to the warmest stream temperatures. Our results suggest that competition most strongly affected the immature portion of RGCT populations, and this effect was only detectable when temperatures were warmest and energetic stress was likely at its highest. The quadratic relationship between temperature and growth rates also demonstrated that stream temperatures were below as well as above optimal growth temperatures for RGCT. Growth rates in our RGCT populations were influenced by complex interactions of DD and DI effects, and our results suggest that the negative consequences of warming trends associated with climate change on RGCT populations may be exacerbated by DD effects.

New Mexico↗
USGS2021

Invasive Lake Trout reproduction in Yellowstone Lake under an active suppression program

In Yellowstone Lake, predation by invasive Lake Trout Salvelinus namaycush has caused significant abundance declines in native Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri . Lake Trout suppression has been ongoing since 1995; assessment and simulation modeling are used to measure suppression effectiveness and guide efforts. Lake Trout reproduction demographics are linked to these modeling efforts via quantification of the population stock–recruitment relationship. To improve estimation of this relationship for Lake Trout in Yellowstone Lake, we assessed reproduction demographics by quantifying spawning periodicity, size at maturity, and female fecundity. Histological assessment suggested that females with a gonadosomatic index (GSI) >3.0 and males with a GSI >1.0 were capable of spawning. Approximately 65% of mature females appeared to have spawned on an annual cycle. In 2015, the mean absolute and relative fecundities were 4,612 eggs and 1,535 eggs/kg, respectively; temporal differences in relative fecundity (1996, 2006, 2007, and 2015) were not statistically significant. Lake Trout population fecundity has declined from a peak in 2010 due to reduction in abundance of spawners. The estimated population fecundity of approximately 4.7 million eggs in 2020 represents an 81% decline from the mean estimate of previous samples and an 87% reduction from peak population fecundity. Despite declines in population fecundity, age-2 recruitment has increased in recent years; our results suggest these increases are not related to changes in reproductive demographics, but rather are related to increased prerecruitment survival. Our results provide information for understanding temporal variation in spawning stock biomass of Lake Trout in Yellowstone Lake and the capacity of the population to respond to suppression. When responding to an invasive species, fishery managers should recognize that population characteristics (e.g., reproduction demographics, population dynamics) in invaded systems may differ from those in the species’ native range; such differences can influence the effectiveness of management actions and policies.

Wyoming↗
USGS2021

Movement dynamics and survival of stocked Colorado River Cutthroat Trout

The ability of native fish to establish self-sustaining populations when reintroduced to vacant habitats is variable. We evaluated factors that potentially affect the reintroduction success of juvenile Colorado River Cutthroat Trout Oncorhynchus clarkii pleuriticus that were reintroduced to an isolated watershed and were experiencing suboptimal survival and recruitment. We conducted a 3-year mark–recapture study to model annual apparent survival probability as it related to (1) different ex situ rearing strategies and (2) initial release among different habitat types. The use of PIT tags also enabled the quantification of loss via emigration. Apparent survival was highest for small fish that were minimally exposed to ex situ rearing conditions, stocked in small, headwater stream reaches. However, maximum estimates of apparent survival remained low (≤0.38 ± 0.05 [estimate ± SE]) regardless of rearing treatment, stocking location, or interactive effects between covariates. Emigration of stocked fish (<1%) from the study area did not appear to limit their establishment. Our results suggest that variation in stocking and rearing strategy may have some effect on translocation success and the interaction between rearing and stocking strategy highlights the importance of considering the life history stage of stocked individuals when identifying stocking sites. Consistently low annual survival values may be indicative of a larger issue, requiring in-depth evaluation of adaptive potential within our brood source and other factors that potentially limit population persistence.

Wyoming↗
USGS2021

Replacement of the typical artedi form of Coregonus artedi in Lake Huron by endemic shallow-water Ciscoes, including putative hybrids

Various ecomorphs of shallow-water Cisco Coregonus artedi were the dominant fish planktivores in each of the Great Lakes until invasive species and over fishing resulted in extirpations and extinctions. In this paper we describe the present morphological diversity and distribution of shallow-water Ciscoes in each of Lake Huron’s three basins: the main basin, Georgian Bay, and North Channel. Typical artedi , a formerly widespread ecomorph, which had supported the lake’s largest fishery, appears to have been extirpated from all three basins. Three types of shorthead ciscoes, a recently described and variable ecomorph, were extant. One type was morphologically robust and abundant along the north rim of the lake. The second type was large bodied, terete, short finned, and collected at only one location in the main basin. The third type consisted of putative shorthead cisco × typical artedi hybrids, which were widespread in Georgian Bay and the North Channel. Only the putative hybrids were regularly collected in midwater trawls, suggesting they were more-pelagic, which we attribute to an inferred partial ancestry with typical artedi . The putative shorthead cisco × typical artedi hybrids of Georgian Bay and the North Channel have replaced typical artedi to some degree, while shorthead ciscoes in the main basin, though possibly more abundant now than in the past, have not measurably replaced typical artedi . Even with the apparent extirpation of typical artedi , Lake Huron has a greater diversity of shallow-water Ciscoes than any of the other Great Lakes, which we attribute to its more-complex topography.

Lake Huron↗