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USGS2013

Influences of riparian vegetation on trout stream temperatures in central Wisconsin

Summer stream temperatures limit the distribution of Brook Trout Salvelinus fontinalis and are affected by riparian vegetation. We used riparian and instream habitat surveys along with stream temperature loggers placed throughout streams to determine the potential for riparian vegetation shading to increase the length of stream that is thermally suitable for Brook Trout. Twelve streams located throughout central Wisconsin were evaluated in the summers of 2007 and 2008. Across all streams, nonparametric ANCOVA modeling was used to identify spatial temperature patterns within a year for individual stream segments. Riparian tree-vegetated segments had a significantly lower mean change in stream temperature per kilometer of stream compared with grass-vegetated segments during the periods of maximum daily and weekly average temperatures, when we accounted for upstream temperature. Riparian grass-vegetated segments increased on average 1.19°C/km (SE, 0.44) during the maximum daily average temperature period and 0.93°C/km (SE, 0.39) during the maximum weekly average temperature period, whereas tree-vegetated segments decreased 0.48°C/km (SE, 0.39) and 0.30°C/km (SE, 0.25) during those respective time periods. Maximum weekly average temperatures were also modeled with different shading levels using a heat budget temperature model, U.S. Fish and Wildlife Service's Stream Segment Temperature Model. Across 11 study streams (one stream model could not be calibrated), modeled stream temperatures in equilibrium with their environmental conditions ranging from 23.2°C to 28.3°C at 0% shading could be reduced to 18.8–23.5°C with 75% shading. Modeled increases in shade up to 75% from the current average of 34% increased the length of surveyed stream thermally suitable to Brook Trout by 4.9 km on Sucker Creek. We conclude that riparian forests are important for maintaining thermal conditions suitable for Brook Trout in central Wisconsin streams and can be managed to increase the amount of stream habitat thermally suitable for Brook Trout.

Wisconsin↗

USGS2001

Fall and winter habitat use and movement by Columbia River redband trout in a small stream in Montana

We used radiotelemetry to quantify the movements and habitat use of resident adult Columbia River redband trout Oncorhynchus mykiss gairdneri (hereafter, redband trout) from October to December 1997 in South Fork Callahan Creek, a third‐order tributary to Callahan Creek in the Kootenai River drainage in northwestern Montana. All redband trout ( N = 23) were consistently relocated in a stream reach with moderate gradient (2.3%) near the site of original capture. Some fish ( N = 13) displayed sedentary behavior, whereas others were mobile ( N = 10). The mean total distance moved during the study for all fish combined was 64 m (SD = 105 m; range, 0–362 m), and the mean home range from October through December was 67 m (SD = 99 m; range, 5–377 m). Thirteen redband trout made short upstream and downstream movements (mean total movement = 134 m; range, 8–362 m) that were related to habitat use. Mobile fish commonly migrated to complex pools that spanned the entire channel width (primary pools). Eight of 10 fish that did not change habitat location occupied primary pools, whereas the remaining 2 fish occupied lateral pools. Fish commonly overwintered in primary pools dominated by cobble and boulder substrates that contained large woody debris. As water temperatures decreased from 3.2–6.3°C in October to 0–3.8°C in November and December, we found a 29% average increase (46–75%) in the proportional use of primary pool habitats. The lack of extensive movement and small home ranges indicate that adult redband trout found suitable overwintering habitat in deep pools with extensive amounts of cover within a third‐order mountain stream. Resource managers who wish to protect overwintering habitat features preferred by redband trout throughout their limited range in streams affected by land management practices could apply strategies that protect and enhance pool habitat and stream complexity.

Montana↗

USGS2003

Winter diel habitat use and movement by subadult bull trout in the upper Flathead River, Montana

We evaluated the diel habitat use and movement of subadult bull trout Salvelinus confluentus by use of radiotelemetry during winter in the upper Flathead River, Montana. Of the 13 monitored bull trout, 12 (92%) made at least one diel movement to other habitat locations during their respective day–night tracking surveys and moved an average of 73% of the time. The median distance moved from day to night locations by the mobile fish was 86 m (range, 27–594 m). Diel shifts in habitat use by nine of the tagged fish were related to light intensity; nocturnal emergence generally commenced immediately after the onset of night, and daytime concealment occurred at daybreak. When diel shifts in microhabitat use occurred, subadult bull trout moved from deep, midchannel areas during the day to shallow, low‐velocity areas along the channel margins without overhead cover at night. Resource managers who wish to protect the overwintering habitat features preferred by subadult bull trout in the upper Flathead River should use natural flow management strategies that maximize and stabilize channel margin habitats at night.

Montana↗

USGS2005

An empirical model for estimating annual consumption by freshwater fish populations

Population consumption is an important process linking predator populations to their prey resources. Simple tools are needed to enable fisheries managers to estimate population consumption. We assembled 74 individual estimates of annual consumption by freshwater fish populations and their mean annual population size, 41 of which also included estimates of mean annual biomass. The data set included 14 freshwater fish species from 10 different bodies of water. From this data set we developed two simple linear regression models predicting annual population consumption. Log-transformed population size explained 94% of the variation in log-transformed annual population consumption. Log-transformed biomass explained 98% of the variation in log-transformed annual population consumption. We quantified the accuracy of our regressions and three alternative consumption models as the mean percent difference from observed (bioenergetics-derived) estimates in a test data set. Predictions from our population-size regression matched observed consumption estimates poorly (mean percent difference = 222%). Predictions from our biomass regression matched observed consumption reasonably well (mean percent difference = 24%). The biomass regression was superior to an alternative model, similar in complexity, and comparable to two alternative models that were more complex and difficult to apply. Our biomass regression model, log10(consumption) = 0.5442 + 0.9962??log10(biomass), will be a useful tool for fishery managers, enabling them to make reasonably accurate annual population consumption predictions from mean annual biomass estimates. ?? Copyright by the American Fisheries Society 2005.

North American Journal of Fisheries Management↗

USGS2005

Low summer water temperatures influence occurrence of naturalized salmonids across a mountain watershed

We investigated relationships between the absence of salmonids and low summer water temperatures across a 150-km2 Rocky Mountain watershed. A model predicting maximum July water temperature (MJT) from measurements of perennial stream length, wetted width, and midrange basin elevation was developed from temperature data obtained at 20 sites across the watershed. The model was used to predict MJT in 75 reaches across the watershed where salmonids were sampled. The lowest predicted MJT in reaches where age-0 and juvenile-adult brook trout Salvelinus fontinalis were observed was 9??C. The lowest predicted MJT in reaches where age-0 progeny of the genus Oncorhynchus spp. (i.e., rainbow trout O. mykiss or cutthroat trout O. clarkii) were observed was 13??C and where Oncorhynchus spp. adults where observed was 12??C. The probability of occurrence of both age-0 and adult brook trout and Oncorhynchus spp. increased as MJT increased above these thresholds. Our results indicate that low MJT in some portions of a mountain watershed can be related to the absence of salmonids. Consequently, data on MJT may provide managers with a means of assessing where summer water temperatures are not suitable for establishment of naturalized salmonid populations. ?? Copyright by the American Fisheries Society 2005.

North American Journal of Fisheries Management↗

USGS2020

Benthic suffocation of invasive lake trout embryos by fish carcasses and sedimentation in Yellowstone Lake

Introduced Lake Trout Salvelinus namaycush threaten native Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri in Yellowstone Lake, Yellowstone National Park, where gill nets have been used to suppress subadult and adult Lake Trout since 1995. However, survival of embryonic and larval life history stages can have profound effects on the population dynamics of Lake Trout. Inducing additional mortality at those stages, especially if used in concert with intensive gillnetting of older fish, could enhance overall suppression efforts. Therefore, we conducted controlled field experiments at Yellowstone Lake to systematically evaluate the effects of sediment deposition and ground Lake Trout carcass deposition on Lake Trout embryos in pre-positioned incubators. Sediment deposition caused dissolved oxygen concentrations to decline below lethal levels for a prolonged overwinter period (92 d). Embryo mortality among overwintering incubators varied from 97.0 ± 5.3% (mean ± SE) at the substrate surface to 100.0 ± 0.0% at 20 cm below the substrate surface. Decomposition of ground carcass material on spawning sites caused dissolved oxygen concentrations to decline to lethal levels (<3.4 mg/L) for about 9 d after biomass application rates of 14 and 28 kg/m 2 in treatment plots. Exposure to ground carcass material resulted in 100.0 ± 0.0% embryo mortality at the substrate surface and within interstices 20 cm below the surface in 14- and 28-kg/m 2 biomass treatments. Embryo mortality was probably caused by hypoxic conditions within substrates in both experiments. The deposition of sediment and ground Lake Trout carcass material on Lake Trout spawning sites in Yellowstone Lake could provide an additional source of mortality in ongoing Lake Trout suppression efforts. These methods may also be beneficial in other systems when incorporated in an integrated pest management approach targeting multiple life history stages of invasive freshwater fish.

Wyoming↗

USGS2023

Silver carp herding: A telemetry evaluation of efficacy and implications for design and application

Removal of invasive Silver Carp Hypophthalmichthys molitrix is a primary control action in North America. Strong avoidance responses to underwater sound and electricity have been shown to facilitate herding and mass removal of these fish. We conducted a telemetry study on a closed population of Silver Carp (i.e., 10 telemetered fish) to assess fine-scale movement responses to herding stimuli. Two herding boats traveled along bank-to-bank transects through the study area (longitudinal progression rate = 0.37 m/s) emitting sound and electricity (“combination technique”) or no added stimuli (“control”). The combination technique was most effective in terms of increasing fish presence (2.2 x the control) in the refuge-zones when herding had concluded and effective range (i.e., fish reaction distance; 1.6 x the control) relative to the herding boats. Fish median (~1 m/s) and maximum (~2 m/s) swimming velocity was relatively stable across fixed effects, except for the negative influence of water depth on maximum velocity. Water depth also exhibited a negative effect on fish reaction distance. Our results suggest effective range of the combination technique was conservatively 200 m (~20 dB re 1 μPa > ambient level) when accounting for water depth in the study area. Herding deployments less than 1 m/s (longitudinal progression) could control fish passing and maintain fish movements towards an intended location. Information provided herein can serve to assist planning, design, and application of herding efforts used to manage, control, and remove these invasive fish.

Kentucky↗

USGS2017

Survival, movement, and distribution of juvenile Burbot in a tributary of the Kootenai River

Burbot Lota lota in the lower Kootenai River, Idaho, have been the focus of extensive conservation efforts, particularly the release of hatchery-reared juvenile Burbot into small tributaries. The Idaho Department of Fish and Game installed a fixed PIT antenna on Deep Creek, a tributary of the Kootenai River, to evaluate movement of juvenile Burbot to the Kootenai River. Since then, approximately 12,000 juvenile Burbot have been PIT-tagged and released into Deep Creek, but few Burbot have been detected at the antenna, thus raising questions about their fate in the creek. The objectives of this study were to evaluate survival, movement, and distribution of Burbot released into Deep Creek. During 2014, 3,000 age-0, 200 age-1, 16 age-2, and 16 age-4 Burbot were released at two different locations; during 2015, 3,000 age-0 Burbot were released at six different locations (i.e., 500 fish/site). Five additional stationary PIT tag antennas were installed on Deep Creek prior to stocking in 2014. Mobile PIT tag antennas were used to survey the creek in 2015 and 2016. A Barker model in Program MARK was used to estimate survival. Stationary and mobile PIT tag antennas relocated 3,372 (56%) of the Burbot released in Deep Creek during 2014 and 2015. Eighty-eight percent of PIT tags relocated during mobile surveys were relocated within 1 km of a release location. Mobile surveys of release locations in Deep Creek suggested poor dispersal from stocking locations. Survival did not vary across years or release groups. Initial 7-month survival in Deep Creek was 0.27, and survival improved to 0.63 after the first 7 months. Although survival did not differ between years or among release groups, managers may consider releasing Burbot at lower densities across multiple locations.

Idaho↗

USGS2004

Injury and mortality of warmwater fishes immobilized by electrofishing

Most studies of injury associated with electrofishing have focused on salmonids: few have given attention to warmwater fishes. Under controlled laboratory conditions, we treated bluegill Lepomis macrochirus, channel catfish Ictalurus punctatus, and largemouth bass Micropterus salmoides of various sizes to duty cycles ranging from 1.5% to 100%. This range of duty cycles represented continuous DC and pulsed-DC frequencies ranging from 15 to 110 Hz and pulse durations of 1 to 6 ms. At each duty cycle, fish were exposed to power densities in excess of those required to immobilize them within 3 s, and we subsequently determined the incidence of hemorrhage, spinal injury, and mortality. Incidence of hemorrhage averaged 3% (range, 0-25%), differed among species, and was not related to duty cycle or fish size. Incidence of spinal injury averaged 3% (range, 0-22%) and mortality averaged 10% (range, 0-75%); both differed among species and were related to duty cycle, fish size, and interactions among these variables. Largemouth bass was the species most vulnerable to hemorrhage, spinal injury, and mortality, channel catfish the least vulnerable; bluegills exhibited effects that were intermediate. Small centrarchids were especially susceptible to mortality. Fish tetanized by the electrical treatment were more likely to experience injury and mortality than fish that were only narcotized. However, mortality was not related to the injuries studied because hemorrhage and spinal injuries were similar in fish that survived electroshock and in those that died. We suggest that electrofishing with intermediate to high duty cycles could reduce electrofishing-induced injury and mortality to warmwater fish. Additionally, the power output and electrode system should be managed to induce narcosis and prevent tetany and to avoid the large peak powers required to immobilize small individuals.

North American Journal of Fisheries Management↗

USGS2008

Fish assemblages in a western Iowa stream modified by grade control structures

Over 400 riprap grade control structures (GCSs) have been built in streams of western Iowa to reduce erosion and protect bridges, roads, and farmland. In conjunction with a companion study evaluating fish passage over GCSs in Turkey Creek, we evaluated the differences in fish assemblage and habitat characteristics in reaches immediately downstream from GCSs (GCS sites) and reaches at least 1 km from any GCS (non-GCS sites). The GCS sites were characterized by greater proportions of pool habitat, maximum depths, fish biomass, and abundance of juvenile largemouth bass Micropterus salmoides than were non-GCS sites. Index of biotic integrity (IBI) scores were poor or fair (<43 on a 0-100 scale) and not significantly different between the GCS and non-GCS sites. Additionally, we investigated both the longitudinal changes in fish assemblages in this GCS-fragmented stream and the changes in fish assemblages after slope modifications of three GCSs to facilitate fish passage. Thirteen fish species were present throughout the study area, whereas another 15 species exhibited truncated distributions not extending to the most upstream sampling location. After modification of the GCSs, IBI scores increased at seven of nine sites (mean increase =4.6 points). Also, channel catfish Ictalurus punctatus were detected 7.3 km upstream at sites where, 2 years before GCS modification, they had been absent from collections. Given the number and distribution of GCSs in western Iowa streams, understanding the effects of these structures is vital to the conservation and management of fish assemblages in this and other regions where GCSs or similar structures are used. ?? Copyright by the American Fisheries Society 2008.

North American Journal of Fisheries Management↗

USGS2018

Responses of hatchery‐ and natural‐origin adult spring Chinook Salmon to a trap‐and‐haul reintroduction program

The construction of impassable dams severely affected many Pacific salmon Oncorhynchus spp. populations, resulting in reintroduction efforts that are now focused on returning anadromous fish to areas located upstream of these dams. A primary strategy for moving adult salmon and steelhead O. mykiss around a dam or multiple dams involves trapping fish downstream and transporting them to upstream areas (“trap and haul”) for spawning. We conducted a 4‐year radiotelemetry study to evaluate behavior and movement patterns of hatchery‐ and natural‐origin adult spring Chinook Salmon O. tshawytscha after a trap‐and‐haul program was implemented around three dams on the Cowlitz River, Washington. A multistate model was used to describe how factors such as origin, sex, release site location, and discharge affected transition rates to riverine areas where spawning habitat was located. Natural‐origin Chinook Salmon moved upstream from a reservoir release site and entered one of two rivers more quickly and in greater proportions than hatchery‐origin fish. Results from the multistate model indicated that transition rates from the reservoir to the Cowlitz River were 2.2 times higher for natural‐origin Chinook Salmon than for hatchery‐origin fish. About one‐half (49.6%) of the reservoir‐released hatchery‐origin Chinook Salmon moved upstream into the Cowlitz River or the Cispus River during the spawning period. The release of hatchery‐origin Chinook Salmon directly into these rivers increased the percentage of fish with river fates during the spawning period to 72.3–75.4%. Results from the multistate model showed that factors such as release site location, origin, day of year, and discharge were important predictors of transition intensities between specific locations in the study area. These findings illustrate the need to evaluate how salmon and steelhead respond to trap‐and‐haul methods, allowing for better management of reintroduction efforts in the future.

Washington↗

USGS2017

Intra‐annual variability of Silver Carp populations in the Des Moines River, USA

Since their introduction in the 1970s, Silver Carp Hypophthalmichthys molitrix have spread throughout the Mississippi River basin. Management of any species relies on an accurate understanding of population characteristics and dynamics. However, Silver Carp seasonal sampling variation is unknown. Sampling during periods of peak catch rates would facilitate Silver Carp assessment and management, improving monitoring and removal techniques. The objective of this study was to evaluate adult Silver Carp seasonal sampling variation with boat electroshocking and trammel nets. Silver Carp were collected monthly (April–October) during 2014 and 2015 from four locations in the Des Moines River, Iowa. Trammel nets rarely captured Silver Carp (mean ± SE = 4.9 ± 1.6 fish/net; 60% of fish were captured in 6.3% of net sets) and therefore were not included in analyses. Electroshocking catch rates (CPUEs) exhibited a bimodal distribution, with peak CPUEs generally occurring in May, June, and September and lower catch rates observed during July and August. Catch rates were positively related to river discharge at upstream sites but not at downstream sites. Silver Carp size structure was similar among months and sites except at Cliffland, where fish were smaller during August and October compared to earlier in the year. Finally, Silver Carp condition peaked during April and May and decreased throughout the year except at Keokuk, where peaks were observed during both May and August. Although spatiotemporal variability was substantial, these results suggest that sampling of Silver Carp via electroshocking in May–June and September–October generally produces higher catch rates compared to July–August sampling and generates a more representative size structure. Using site‐specific knowledge, monitoring and surveillance programs could more effectively sample during these periods of high vulnerability and densities in order to manage the spread and impacts of Silver Carp at statewide and regionwide scales.

Iowa↗

USGS2008

Habitat use of juvenile pallid sturgeon and shovelnose sturgeon with implications for water-level management in a downstream reservoir

Natural recruitment of pallid sturgeon Scaphirhynchus albus has not been observed in the Missouri River above Fort Peck Reservoir, Montana, for at least 20 years. To augment the population, age-1 hatchery-reared juvenile pallid sturgeon were released in 1998. The objective of this study was to evaluate the habitat use of these fish and compare it with that of indigenous shovelnose sturgeon S. platorynchus. Twenty-nine juvenile pallid sturgeon and 21 indigenous shovelnose sturgeon were implanted with radio transmitters in 2003 and 2004. The two species showed no differences in habitat use in terms of mean depth, cross-sectional relative depth, longitudinal relative depth, column velocity, bottom velocity, and channel width. However, there were seasonal differences within both species for cross-sectional relative depth, column velocity, and channel width. Both shovelnose sturgeon and juvenile pallid sturgeon were primarily associated with silt and sand substrate. However, shovelnose sturgeon were associated with gravel and cobble substrate more than juvenile pallid sturgeon. Shovelnose sturgeon and juvenile pallid sturgeon both selected reaches without islands and avoided reaches with islands; the two species also selected main-channel habitat and avoided secondary channels. Mean home range was similar between juvenile pallid sturgeon (15 km; 90% confidence interval, ??5.0 km) and shovelnose sturgeon (16.5 km; ??4.7 km). Spatial distribution differed between the two species, with shovelnose sturgeon using upstream areas more often than juvenile pallid sturgeon. Twenty-eight percent of juvenile pallid sturgeon frequented 60 km of lotie habitat that would be inundated by Fort Peck Reservoir at maximum pool. Stocking juvenile pallid sturgeon can successfully augment the wild pallid sturgeon population in the Missouri River above Fort Peck Reservoir, which is crucial to the long-term recovery of the species. However, water-level management in downstream reservoirs such as Fort Peck can influence the amount of habitat available for pallid sturgeon. ?? Copyright by the American Fisheries Society 2008.

North American Journal of Fisheries Management↗

USGS1994

Development of an antimycin-impregnated bait for controlling common carp

The common carp Cyprinus carpio is a major problem for fisheries and wildlife managers because its feeding behavior causes degradation of valuable fish and waterfowl habitat. This study was designed to evaluate the effectiveness of an antimycin‐impregnated bait for control of common carp. The toxic bait contained fish meal, a binder, antimycin, and water. The ingredients were mixed together and made into pellets. This bait was force‐fed to common carp or administered in a pond environment, where fish voluntarily fed on the bait. The lowest lethal dose in the force‐feeding study was 0.346 mg antimycin/kg of fish and doses that exceeded 0.811 mg antimycin/kg were toxic to all fish. On three occasions, adult common carp held in 0.004‐ha concrete ponds were offered 10 g of toxic bait containing 5.0, 7.5, and 10 mg antimycin/g of bait and the mean mortalities 96 h later were 21, 35, and 51%, respectively. Three tests were conducted in 0.04‐ha earthen ponds each containing 100 adult common carp; these fish were offered 50 g of the toxic bait that contained 10 mg antimycin/g, and the mean mortalities (96 h) were 19, 32, and 74%. Toxic baits should be used in conjunction with other management techniques, and only when common carp are congregated and actively feeding, and when few nontarget bottom‐feeding species are present.

North American Journal of Fisheries Management↗

USGS2003

Historic and modern abundance of wild lean lake trout in Michigan waters of Lake Superior: Implications for restoration goals

Populations of lake trout Salvelinus namaycush in Lake Superior collapsed in the late 1950s due to overfishing and predation by sea lampreys Petromyzon marinus . A binational effort to restore the lean morphotype of lake trout began with the stocking of hatchery-reared fish followed by the chemical control of sea lampreys and closure of the commercial fishery. Previous comparisons of the contemporary abundance of wild lean lake trout with that from historic commercial fishery statistics indicate that abundance was higher historically. However, this conclusion may be biased because several factors—the inclusion of siscowet (the “fat” morphotype of lake trout) in the catch statistics, the soak time of nets, seasonal effects on catch per effort, and the confounding effects of effort targeted at lake whitefish Coregonus clupeaformis —were not accounted for. We developed new indices of historic lean lake trout abundance that correct for these biases and compared them with the assessment data from 1984 to 1998 in Michigan waters of Lake Superior. The modern (1984–1998) abundance of wild lean lake trout is at least as high as that during 1929–1943 in six of eight management areas but lower in one area. Measures to promote and protect naturally reproducing populations have been more successful than previously realized.

North American Journal of Fisheries Management↗

USGS2025

Population dynamics of White Sturgeon in the upper Snake River, Idaho: Evaluation of management options for a harvest fishery

Objective Understanding how fish populations will respond to management actions is critical for making effective management decisions. This study provides important information regarding population demographics for a nonnative, hatchery-implemented population of White Sturgeon Acipenser transmontanus . We investigated the population dynamics of White Sturgeon in the upper Snake River, Idaho, and developed an age-structured population model to evaluate potential stocking and harvest scenarios (e.g., length limits and annual quotas). Methods White Sturgeon were sampled from June to October 2022 and from June to August 2023 using angling (i.e., rod and reel) and setlines from a 260-km-long section of the Snake River. Capture histories from 261 known-age White Sturgeon informed age and growth analysis and an evaluation of movement trends. A closed-population capture–recapture model and an estimate of setline-specific catchability were used to estimate the total abundance of White Sturgeon in the upper Snake River. Apparent survival for the population was estimated using a Cormack–Jolly–Seber model. Finally, a population model was parameterized using information on the population dynamics of White Sturgeon in the upper Snake River. The model was used to estimate the effects of varying stocking rates and harvest scenarios (i.e., harvest slot of 76–122 cm fork length [FL] and annual quotas of 0–25 White Sturgeon harvested) on the population. Results In total, 340 individual White Sturgeon were captured throughout the study area, with 181 recapture events. Individuals varied in FL from 54 to 205 cm, and the mean relative weight for captures was 105.2 (SD = 14.4), suggesting relatively high body condition. Age varied from 2 to 25 years, and White Sturgeon moved an average of 8.1 km (SD = 23.5) downstream from stocking locations. Estimated abundance of White Sturgeon in the tailwaters of American Falls Dam was 428 fish (95% CI = 403–463). That abundance estimate was used to inform a total abundance estimate of 887 White Sturgeon (95% CI = 835–960) in the study area. Apparent annual survival was 0.79 (95% CI = 0.64–0.89). A stocking rate of 285 age-2 White Sturgeon/year was necessary to maintain current abundance. For every five fish harvested (harvest slot = 76–122 cm FL) per year, estimated abundance decreased by about 2.2% over 20 years. Conclusions Our research identified fast growth of White Sturgeon relative to other populations and relatively high mortality for a White Sturgeon population without exploitation. Also, like other studies evaluating harvest, a population model was used to illustrate the effect of varying rate functions on a fishery. The age-structured population model suggested that a harvest fishery is possible while still meeting management goals for the upper Snake River White Sturgeon fishery.

Idaho↗

USGS1995

Abundance indices for determining the status of lake trout restoration in Michigan waters of Lake Superior

Self-sustaining populations of lake trout Salvelinus namaycush have returned to most areas in Lake Superior, but progress toward achieving historic commercial yields has been difficult to measure because of unrecorded losses to predation by sea lamprey Petromyzon marinus and to fisheries. Consequently, we developed restoration targets (catch per effort, CPE; geometric mean number per kilometer of 114-mm stretch-meaure gill net during 1929-1943, when historic yields were sustained) from linear relationships between CPE in commercial and assessment fisheries in Michigan. Target CPEs for lake trout restoration were higher and less variable than the modern CPEs in all areas. Modern CPEs generally increased during the 1970s and early 1980s but declined during the late 1980s and early 1990s. Modern CPEs were highest in western Michigan from the Keweenaw Peninsula to Marquette (71 to 81% of target CPEs), but coefficients of variation (CV,SD/mean) of mean CPEs were 1.4 to 2.4 times greater than target CVs. Around Munising, the modern CPE was lower (41% of the target CPE), whereas the CV was 1.9 times greater than the target CV. Around Grand Marais, the modern CPE was lowest among all areas (17% of the target CPE), but the CV was nearly the same (1.1 times the target CV). In Whitefish Bay, the modern CPE was only 28% of the target CPE and the CV was 9.0 times greater, though the modern period was based on only the years 1979-1982 and 1984-1985. Further progress in restoration in most areas can be achieved only if fishery managers adequately protect existing stocks of wild fish from sea lamprey predation and fishery exploitation.

North American Journal of Fisheries Management↗

USGS2019

Population ecology and evaluation of suppression scenarios for an introduced Utah Chub population

Introduced Utah Chub Gila atraria were first sampled in Henrys Lake, Idaho, in 1993, and their presence in the system is a concern given possible interactions with sport fishes. Our objective was to describe the population dynamics of Utah Chub in Henrys Lake. A total of 362 Utah Chub was sampled via gill nets, with an average catch rate of 20.5 fish/net-night (SE = 6.0) during May 2016. Average TL was 210 mm (SE = 3), and average weight was 134 g (SE = 5). Pectoral fin rays were used to provide estimates of growth and age structure. Utah Chub varied in age from 2 to 12 years, and recruitment was stable (recruitment coefficient of determination = 0.96). Estimated total annual mortality was 40% (SE = 4%). Fecundity of Utah Chub in Henrys Lake increased with length and varied from 6,232 to 156,797 eggs/female. Age-structured population models were constructed using the demographics data, and estimated average population growth rate over a 10-year period was 1.17. This study provides a comprehensive description of Utah Chub population dynamics and insight on their management in systems where they are not native. This information is not only useful for guiding management actions but also serves to further our understanding of Utah Chub ecology.

Idaho↗