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USGS2015

Effects of gill-net trauma, barotrauma, and deep release on postrelease mortality of Lake Trout

Unaccounted postrelease mortality violates assumptions of many fisheries studies, thereby biasing parameter estimates and reducing efficiency. We evaluated effects of gill-net trauma, barotrauma, and deep-release treatment on postrelease mortality of lake trout Salvelinus namaycush . Lake trout were captured at depths up to 65 m with gill nets in Priest Lake, Idaho, and held in a large enclosure for 10–12 d. Postrelease mortality was the same for surface-release–and deep-release–treated fish (41%). Mixed-effects logistic regression models were used to evaluate effects of intrinsic and environmental factors on the probability of mortality. Presence of gill-net trauma and degree of barotrauma were associated with increased probability of postrelease mortality. Smaller fish were also more likely to suffer postrelease mortality. On average, deep-release treatment did not reduce postrelease mortality, but effectiveness of treatment increased with fish length. Of the environmental factors evaluated, only elapsed time between lifting the first and last anchors of a gill-net gang (i.e., lift time) was significantly related to postrelease mortality. Longer lift times, which may allow ascending lake trout to acclimate to depressurization, were associated with lower postrelease mortality rates. Our study suggests that postrelease mortality may be higher than previously assumed for lake trout because mortality continues after 48 h. In future studies, postrelease mortality could be reduced by increasing gill-net lift times and increasing mesh size used to increase length of fish captured.

Idaho↗

USGS2022

Rotenone use and subsequent prey loss lowers Osprey fledging rates via brood reduction

Fisheries managers used the fish toxicant rotenone to eradicate an undesirable brown bullhead ( Ameiurus nebulosus ) population and all other fish species at Hyatt Reservoir, Oregon, on 12 October 1989. This 4-yr study (1988–1990, 1992) compared effects of that rotenone project on Ospreys ( Pandion haliaetus ) nesting at Hyatt Reservoir and nearby Howard Prairie Reservoir (untreated reference)—the latter a reservoir where both brown bullheads and hatchery-released rainbow trout ( Oncorhynchus mykiss ) prospered. Because Hyatt Reservoir was treated after Osprey fall migration in 1989, the first 2 yr (1988 and 1989) yielded pretreatment information: number of Osprey pairs was unchanged and reproductive rates were similar and consistent at the two reservoirs. Yearling fish (200–250 mm) were restocked at Hyatt Reservoir in the spring of 1990 and Ospreys returned each year following rotenone treatment, with no decline in the number of occupied or active nests. The negative effect of the rotenone treatment on Ospreys was short-term, resulting in reduced reproductive rates (young/occupied nest, young/active nest, and young/successful nest) during the first nesting season posttreatment, although hatching rates were not affected. Osprey dive success and prey delivery rates declined sharply in 1990, leading to competition for food among siblings and brood reduction. Osprey reproductive rates and prey delivery rates at Hyatt Reservoir in both 1990 and 1992 remained below the extremely high pretreatment rates, but within the range required for population stability. Serious adverse effects of the fish loss on Osprey reproduction were minimized by: (1) the delay of the rotenone application until after breeding season, (2) the restocking of the treated reservoir in the following spring with some larger (yearling) fish (though the timing was late), (3) the maintenance of a supplemental feeding program for a nesting pair of Bald Eagles ( Haliaeetus leucocephalus ), which minimized kleptoparasitism on Ospreys, and perhaps most important (4) the presence of nearby water bodies, where Osprey obtained some fish in the 1990 and 1992 breeding seasons.

Oregon↗

USGS2019

Trends and carrying capacity of sea otters in Southeast Alaska

Sea otter populations in Southeast Alaska (SEAK) have increased dramatically from fewer than 500 translocated animals in the late 1960s. The recovery of sea otters to ecosystems from which they had been absent has affected coastal food webs, including commercially important fisheries, and thus information on expected growth and equilibrium abundances can help inform resource management. We compile available survey data for SEAK and fit a Bayesian state-space model to estimate past trends and current abundance. Our model improves upon previous analyses by partitioning and quantifying sources of estimation error, accounting for over-dispersion of aerial count data, and providing realistic measurements of uncertainty around point estimates of abundance at multiple spatial scales. We also provide the first estimates of carrying capacity (K) for SEAK, at both regional and sub-regional scales, and analyze growth rates, current population status and expected future trends. At the regional scale, the population increased from 13,221 otters in 2003 (95% credible interval 9,990 – 16,828) to 25,584 otters in 2011 (CI95 18,739 – 33,163). The average annual growth rate in southern SEAK (7.8%) was higher than northern SEAK (2.7%); however, growth varied at the sub-regional scale and there was a negative relationship between growth rates and the number of years sea otters were present in an area. Local populations vary in terms of current densities and expected future growth: the mean estimated density at K was 4.2 (1.58) sea otters per km2 of habitat (defined as the sub-tidal benthos between 0-40m depth) and current densities correspond on average to 50% of projected equilibrium values (range = 1% to 97%) with the earliest-colonized sub-regions tending to be closer to K. Assuming a similar range of equilibrium densities for currently un-occupied habitats in SEAK, the projected value of K for all of SEAK is 74,650 sea otters (CI95 =36,778–136,506). Future analyses can improve upon the precision of K estimates by employing more frequent surveys at index sites and incorporating environmental covariates into the process model to generate habitat-specific estimates of equilibrium density.

Alaska↗

USGS2021

Across borders: External factors and prior behaviour influence North Pacific albatross associations with fishing vessels

Understanding encounters between marine predators and fisheries across national borders and outside national jurisdictions offers new perspectives on unwanted interactions to inform ocean management and predator conservation. Although seabird–fisheries overlap has been documented at many scales, remote identification of vessel encounters has lagged because vessel movement data often are lacking. Here, we reveal albatrosses–fisheries associations throughout the North Pacific Ocean. We identified commercial fishing operations using Global Fishing Watch data and algorithms to detect fishing vessels. We compiled GPS tracks of adult black-footed Phoebastria nigripes and Laysan Phoebastria immutabilis albatrosses, and juvenile short-tailed albatrosses Phoebastria albatrus . We quantified albatrosses-vessel encounters based on the assumed distance that birds perceive a vessel (≤30 km), and associations when birds approached vessels (≤3 km). For each event we quantified bird behaviour, environmental conditions and vessel characteristics and then applied Boosted Regression Tree models to identify drivers and the duration of these associations. In regions of greater fishing effort short-tailed and Laysan albatrosses associated with fishing vessels more frequently. However, fishing method (e.g. longline, trawl) and flag nation did not influence association prevalence nor the duration short-tailed albatrosses attended fishing vessels. Laysan albatrosses were more likely to approach longer vessels. Black-footed albatrosses were the most likely to approach vessels (61.9%), but limited vessel encounters ( n = 21) prevented evaluation of meaningful explanatory models for this species of high bycatch concern. Temporal variables (time of day and month) and bird behavioural state helped explain when short-tailed albatrosses were in close proximity to a vessel, but environmental conditions were more important for explaining interaction duration. Laysan albatrosses were more likely to associate with vessels while searching and during the last 60% (by time) of their trips. Our results provide specific species–fisheries insight regarding contributing factors of high-risk associations that could lead to bycatch of albatrosses within national waters and on the high seas. Policy implications . Given the availability of Global Fishing Watch data, our analysis can be applied to other marine predators—if tracking data are available—to identify spatio-temporal patterns, vessel specific attributes and predator behaviours associated with fishing vessel associations, thus enabling predictive modelling and targeted mitigation measures.

Journal of Applied Ecology↗

USGS2022

Population dynamics of Yellowstone Cutthroat Trout in Henrys Lake, Idaho

Yellowstone Cutthroat Trout (YCT) Oncorhynchus clarkii bouvieri is a species with significant ecological and recreational value. In many YCT fisheries, managers are tasked with balancing angler expectations and fish conservation. Henrys Lake supports a popular trophy trout fishery, but the increase of nonnative Utah Chub Gila atraria has caused concern for YCT. We summarized long-term trends in abundance, length structure, body condition, and growth of YCT to evaluate the effect of Utah Chub. Additionally, we investigated abiotic and biotic factors influencing YCT. We examined archived hard structures to provide a comprehensive evaluation of changes in age and growth of YCT in the system. We used stocking records and catch rates of Utah Chub and trout in Henrys Lake as covariates to explain changes in YCT catch rates and growth. Catch rates varied from 1.5 to 15.4 YCT per net night during the 2002 to 2020 sampling period, but we did not identify consistent patterns. Length structure was consistently dominated by stock- to quality-length fish, and we captured few fish >600 mm in total length. Relative weight of YCT was decreased from a mean ± standard deviation (SD) of 115.9 ± 16.5 in 2004 to 93.2 ± 8.2 in 2020. The age of YCT varied between 1 and 11 years; fish that we captured during 2010 to 2020 were the oldest. The majority of fish that we sampled were age 4 and younger. Total annual mortality of age-2 and older YCT was higher than other Cutthroat Trout populations (i.e., 0.70 during 2002 to 2010 and 0.60 during 2011 to 2020). Based on regression models, we identified positive relationships between catch rates of YCT, Brook Trout Salvelinus fontinalis, and Rainbow Trout Oncorhynchus mykiss × YCT hybrid trout. We observed negative relationships between growth of YCT and abundance of Utah Chub and Brook Trout. Although we identified negative relationships, YCT growth in recent decades is as fast as or faster than earlier time periods. Results from this research suggest that major changes in YCT population dynamics are not evident over the last 20 years. This study provides insight into the factors influencing an adfluvial trout population. In particular, results from this research may be useful for managers of systems where Utah Chub have been introduced.

Idaho↗

USGS2013

Reliability of fish size estimates obtained from multibeam imaging sonar

Multibeam imaging sonars have considerable potential for use in fisheries surveys because the video-like images are easy to interpret, and they contain information about fish size, shape, and swimming behavior, as well as characteristics of occupied habitats. We examined images obtained using a dual-frequency identification sonar (DIDSON) multibeam sonar for Atlantic sturgeon Acipenser oxyrinchus oxyrinchus , striped bass Morone saxatilis , white perch M. americana , and channel catfish Ictalurus punctatus of known size (20–141 cm) to determine the reliability of length estimates. For ranges up to 11 m, percent measurement error (sonar estimate – total length)/total length × 100 varied by species but was not related to the fish's range or aspect angle (orientation relative to the sonar beam). Least-square mean percent error was significantly different from 0.0 for Atlantic sturgeon ( x̄ = −8.34, SE = 2.39) and white perch ( x̄ = 14.48, SE = 3.99) but not striped bass ( x̄ = 3.71, SE = 2.58) or channel catfish ( x̄ = 3.97, SE = 5.16). Underestimating lengths of Atlantic sturgeon may be due to difficulty in detecting the snout or the longer dorsal lobe of the heterocercal tail. White perch was the smallest species tested, and it had the largest percent measurement errors (both positive and negative) and the lowest percentage of images classified as good or acceptable. Automated length estimates for the four species using Echoview software varied with position in the view-field. Estimates tended to be low at more extreme azimuthal angles (fish's angle off-axis within the view-field), but mean and maximum estimates were highly correlated with total length. Software estimates also were biased by fish images partially outside the view-field and when acoustic crosstalk occurred (when a fish perpendicular to the sonar and at relatively close range is detected in the side lobes of adjacent beams). These sources of bias are apparent when files are processed manually and can be filtered out when producing automated software estimates. Multibeam sonar estimates of fish size should be useful for research and management if these potential sources of bias and imprecision are addressed.

Journal of Fish and Wildlife Management↗

USGS2020

Carbon dioxide-induced mortality of four species of North American fishes

Fisheries managers have a growing interest in the use of carbon dioxide (CO 2 ) as a tool for controlling invasive fishes. However, limited published data exist on susceptibility of many commonly encountered species to elevated CO 2 concentrations. Our objective was to estimate the 24-h 50% lethal concentration (LC 50 ) and 95% lethal concentration (LC 95 ) of CO 2 for four fishes (Rainbow Trout Oncorhynchus mykiss , Common Carp Cyprinus carpio , Channel Catfish Ictalurus punctatus , and Westslope Cutthroat Trout Oncorhynchus clarkii lewisi ). In the laboratory, we exposed juvenile fish to a range of CO 2 concentrations for 24 h in unpressurized, flow-through tanks. We developed a Bayesian hierarchical model to estimate the dose-response relationship for each fish species with associated uncertainty, and estimated 24-h LC 50 and LC 95 values based on laboratory trials for each species. The minimum concentration inducing mortality differed among cold water–adapted species and warm water–adapted species groups: 150 mg CO 2 /L for Westslope Cutthroat Trout and Rainbow Trout and 225 mg CO 2 /L for Common Carp and Channel Catfish. We observed complete mortality at 275 mg CO 2 /L (38,672 microatmospheres [μatm]), 225 mg CO 2 /L (30,711 μatm), and 495 mg CO 2 /L (65,708 μatm [Common Carp]; 77,213 μatm [Channel Catfish]) for Westslope Cutthroat Trout, Rainbow Trout, and both Common Carp and Channel Catfish, respectively. There was evidence of a statistical difference between the 24-h LC 95 values of Westslope Cutthroat Trout and Rainbow Trout (245.0 [222.2–272.2] and 190.6 [177.2–207.8] mg CO 2 /L, respectively). Additionally, these values were almost half the estimated 24-h LC 95 values for Common Carp and Channel Catfish (422.5 [374.7–474.5] and 434.2 [377.2–492.2] mg CO 2 /L, respectively). Although the experimental findings show strong relationships between increased CO 2 concentration and higher mortality, additional work is required to assess the efficacy and feasibility of a CO 2 application in a field setting.

Journal of Fish and Wildlife Management↗

USGS2014

Developing and testing temperature models for regulated systems: a case study on the Upper Delaware River

Water temperature is an important driver of many processes in riverine ecosystems. If reservoirs are present, their releases can greatly influence downstream water temperatures. Models are important tools in understanding the influence these releases may have on the thermal regimes of downstream rivers. In this study, we developed and tested a suite of models to predict river temperature at a location downstream of two reservoirs in the Upper Delaware River (USA), a section of river that is managed to support a world-class coldwater fishery. Three empirical models were tested, including a Generalized Least Squares Model with a cosine trend (GLScos), AutoRegressive Integrated Moving Average (ARIMA), and Artificial Neural Network (ANN). We also tested one mechanistic Heat Flux Model (HFM) that was based on energy gain and loss. Predictor variables used in model development included climate data (e.g., solar radiation, wind speed, etc.) collected from a nearby weather station and temperature and hydrologic data from upstream U.S. Geological Survey gages. Models were developed with a training dataset that consisted of data from 2008 to 2011; they were then independently validated with a test dataset from 2012. Model accuracy was evaluated using root mean square error (RMSE), Nash Sutcliffe efficiency (NSE), percent bias (PBIAS), and index of agreement (d) statistics. Model forecast success was evaluated using baseline-modified prime index of agreement (md) at the one, three, and five day predictions. All five models accurately predicted daily mean river temperature across the entire training dataset (RMSE = 0.58–1.311, NSE = 0.99–0.97, d = 0.98–0.99); ARIMA was most accurate (RMSE = 0.57, NSE = 0.99), but each model, other than ARIMA, showed short periods of under- or over-predicting observed warmer temperatures. For the training dataset, all models besides ARIMA had overestimation bias (PBIAS = −0.10 to −1.30). Validation analyses showed all models performed well; the HFM model was the most accurate compared other models (RMSE = 0.92, both NSE = 0.98, d = 0.99) and the ARIMA model was least accurate (RMSE = 2.06, NSE = 0.92, d = 0.98); however, all models had an overestimation bias (PBIAS = −4.1 to −10.20). Aside from the one day forecast ARIMA model (md = 0.53), all models forecasted fairly well at the one, three, and five day forecasts (md = 0.77–0.96). Overall, we were successful in developing models predicting daily mean temperature across a broad range of temperatures. These models, specifically the GLScos, ANN, and HFM, may serve as important tools for predicting conditions and managing thermal releases in regulated river systems such as the Delaware River. Further model development may be important in customizing predictions for particular biological or ecological needs, or for particular temporal or spatial scales.

Delaware, New York, Pennsylvania↗

USGS2015

Initiation of migration and movement rates of Atlantic salmon smolts in fresh water

Timing of ocean entry is critical for marine survival of both hatchery and wild Atlantic salmon ( Salmo salar ) smolts. Management practices and barriers to migration such as dams may constrain timing of smolt migrations resulting in suboptimal performance at saltwater entry. We modeled influences of stocking location, smolt development, and environmental conditions on ( i ) initiation of migration by hatchery-reared smolts and ( ii ) movement rate of hatchery- and wild-reared Atlantic salmon smolts in the Penobscot River, Maine, USA, from 2005 through 2014 using acoustic telemetry data. We also compared movement rates in free-flowing reaches with rates in reaches with hydropower dams and head ponds. We compared movement rates before and after (1) removal of two mainstem dams and (2) construction of new powerhouses. Initiation of movement by hatchery fish was influenced by smolt development, stocking location, and environmental conditions. Smolts with the greatest gill Na + , K + -ATPase (NKA) activity initiated migration 24 h sooner than fish with the lowest gill NKA activity. Fish with the greatest cumulative thermal experience initiated migration 5 days earlier than those with lowest cumulative thermal experience. Smolts released furthest from the ocean initiated migration earlier than those released downstream, but movement rate increased by fivefold closer to the ocean, indicating behavioral trade-offs between initiation and movement rate. Dams had a strong effect on movement rate. Movement rate increased from 2.8 to 5.4 km·h −1 in reaches where dams were removed, but decreased from 2.1 to 0.1 km·h −1 in reaches where new powerhouses were constructed. Movement rate varied throughout the migratory period and was inversely related to temperature. Fish moved slower at extreme high or low discharge. Responses in fish movement rates to dam removal indicate the potential scope of recovery for these activities.

Maine↗

USGS2011

Lake sturgeon response to a spawning reef constructed in the Detroit river

Prior to the First World War, the bi-national Detroit River provided vast areas of functional fish spawning and nursery habitat. However, ongoing conflicting human uses of these waters for activities such as waste disposal, water withdrawals, shoreline development, shipping, recreation, and fishing have altered many of the chemical, physical, and biological processes of the Detroit River. Of particular interest and concern to resource managers and stakeholders is the significant loss and impairment of fish spawning and nursery habitat that led to the decline in abundance of most fish species using this ecosystem. Lake sturgeon ( Acipenser fulvescens ) populations for example, were nearly extirpated by the middle of the 20th century, leaving only a small fraction of their former population. Fisheries managers recognized that the loss of suitable fish spawning habitat is a limiting factor in lake sturgeon population rehabilitation in the Detroit River. In efforts to remediate this beneficial water use impairment, a reef consisting of a mixture of natural rock and limestone was constructed at the upstream end of Fighting Island in 2008. This paper focuses on the response by lake sturgeon to the different replicates of suitable natural materials used to construct the fish spawning habitat at Fighting Island in the Detroit River. Pre-construction fisheries assessment during 2006–2008 showed that along with the presence of adult lake sturgeon, spawning conditions were favorable. However, no eggs were found in assessments conducted prior to reef construction. The 3300 m 2 Fighting Island reef was placed at the upstream end of the island in October of 2008. The construction design included 12 spawning beds of three replicates each consisting of either round rock, small or large (shot-rock) diameter limestone or a mixture thereof. An observed response by spawning lake sturgeon occurred the following year when spawning-ready adults (ripe), viable eggs, and larvae were collected during May and June 2009. Additional eggs and spawning-ready adults were found in 2010 (no larval sampling occurred in 2010) as well as collection of three age-0 juvenile lake sturgeon in bottom trawls fished downstream of the reef during July 2010. Spawning lake sturgeon showed no repeatable preference for any of the four particular substrate types but showed a high degree of preference for the island side of the channel, where faster water current velocities occurred. In 2009, overall lake sturgeon egg densities across all replicates averaged 102 m -2 and seven larvae were found in night drift-net samples. In 2010, average lake sturgeon egg density was 12 m -2 and three age-0 lake sturgeon averaging 120 mm TL were collected in bottom trawls in deepwater (∼8 m depth) downstream from the constructed reef. These results demonstrated successful reproduction by lake sturgeon on a man-made reef and suggested that additions and improvements to fish spawning habitat could enhance reproduction and early life history survival of lake sturgeon in the Detroit River.

Michigan;Ontario↗

USGS2018

Short-term mortality and retention associated with tagging Age-0 walleye using passive integrated transponders (PITs) in the absence of anesthesia

The ability to individually mark juvenile fishes has important implications for fisheries management. For example, marking age-0 Walleye Sander vitreus could provide important information not provided by batch-marking, including individual variation in growth and estimates of length-dependent survival and recruitment. However, the relatively small size of age-0 Walleye in north temperate lakes has precluded use of many common tagging methods that provide information on individual fish (e.g., various anchor tags, jaw tags). Consequently, we evaluated short-term mortality and retention associated with using 12-mm passive integrated transponders (PITs) to mark age-0 Walleye (TL range = 93-216 mm; mean TL = 157 mm) by conducting 48-h within-lake net-pen trials and 7-d hatchery trials during September-October of 2015 and 2016. Age-0 Walleye were not anesthetized prior to PIT tagging. Our assessment allowed us to determine whether post-tagging mortality and PIT retention varied in relation to implant location (i.e., body cavity or pelvic girdle), fish length, and water temperature. During 2015, mean 48-h mortality rate of age-0 Walleye tagged with PITs in the body cavity was low (7%; SE = 3%) and did not differ from that of fish marked with only a fin clip (4%; SE = 2%) and reference fish (2%; SE = 1%). During 2016, mean mortality rates ranged from 2% (reference fish) to 6% (PIT inserted into pelvic girdle) and did not differ among treatments. During both years, mortality rates for nearly all treatments were highest (> 13%) when water temperatures were {greater than or equal to} 20°C, but decreased below 5% when water temperatures were {less than or equal to} 17°C. During 2016, dead age-0 Walleye in both PIT treatments were smaller than fish that survived. During the 7-d hatchery trials, mean mortality rates were higher for age-0 Walleye with PITs inserted into the body cavity (13%; SE = 4%) than fish that received a PIT in the pelvic girdle (4%; SE = 1%) and reference fish (4%; SE = 2%). Retention of PITs was high (> 96%) during all net-pen and hatchery trials. Collectively, our results suggest that PITs can be used to tag age-0 Walleye without anesthesia with the expectations of high initial retention and low mortality. Mortality rates may be minimized by implanting PITs into the pelvic girdle when water temperatures are {less than or equal to} 17°C.

Journal of Fish and Wildlife Management↗

USGS2023

Natal contributions of Kokanee salmon to Flaming Gorge Reservoir, Wyoming–Utah: An evaluation using otolith microchemistry

In a system that uses supplemental stocking to enhance a fishery that serves a dual purpose, an understanding of the contributions from natural and hatchery-produced fish is important so that hatchery resources can be appropriately allocated. Kokanee Oncorhynchus nerka were first stocked in Flaming Gorge Reservoir (FGR), Wyoming–Utah, in 1963 and serve a dual purpose as a prey resource and sport fish. Although natural recruitment occurs in the reservoir, a supplemental stocking program was initiated in 1991. We sought to identify the natal origin (i.e., natural, hatchery) of kokanee in FGR using otolith microchemistry. We evaluated return to the creel, composition of spawning aggregates, and growth of kokanee in FGR and focused on differences associated with natal origin. We analyzed kokanee otoliths that we collected from hatcheries ( n = 60) and FGR ( n = 1,003) for the strontium isotope ratio, 87 Sr/ 86 Sr, using laser ablation and a multicollector inductively coupled plasma mass spectrometer. We conducted Kruskal–Wallis tests to compare the strontium isotope ratios from the otolith edge of kokanee that we sampled from hatcheries and FGR. Based on 87 Sr/ 86 Sr ratios, we could distinguish natural-origin kokanee from 11 of the 12 hatcheries ( P < 0.01); however, the Wigwam Hatchery was not significantly different from FGR ( P = 0.84). We used model-based discriminant function analysis to assign natal origins for kokanee caught in FGR. Hatchery contribution to the population at large varied from 21 to 50% among year classes from 2014 to 2018. The percentage of hatchery origin kokanee in the creel (18–50%) was similar to what we observed in the population. Hatchery-produced kokanee contributed a higher proportion to tributary-spawning aggregates (40–90%) than shoreline-spawning aggregates (19–58%) by sample year. Growth of natural and hatchery kokanee was similar, suggesting similar performance in the system. Results from this study identify that hatchery supplementation contributes to the population and recreational harvest of kokanee in FGR. This research also provides insight into the ecology of kokanee that is useful for better understanding kokanee population dynamics in reservoir systems.

Utah, Wyoming↗