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USGS2003

Physiological responses of juvenile rainbow trout to fasting and swimming activity: Effects on body composition and condition indices

The physiological traits that allow fish to survive periods of limited food resources are poorly understood. We assessed changes in proximate body composition, relative organ mass, blood metabolites, and relative weight (Wr) of sedentary and actively swimming (15 cm/s) juvenile rainbow trout (154-182 mm total length) over 147 d of fasting. Fasting caused measurable responses that were augmented when fish were swimming. Lipids and plasma triacylglycerides declined over time. Proteins were catabolized simultaneously with lipid reserves, but ammonia concentrations in plasma did not increase. The liver somatic index (LSI) did not change substantially over 105 d, suggesting that gluconeogenesis maintained blood glucose concentrations and hepatic glycogen reserves for a substantial period of fasting. The gut somatic index (GSI) and Wr declined linearly during fasting, but the LSI did not decline until after 105 d of fasting. Consequently, the use of different body condition indices could lead to different conclusions about the condition of juvenile rainbow trout. Swimming activity caused fish to have lower lipid and protein reserves than those of sedentary fish. No mortalities were observed among sedentary fish, but mortalities occurred among actively swimming fish after 97 d of fasting when 3.2% or less lipid remained in their bodies. Body condition indices did not account for differences in proximate body composition between sedentary and actively swimming fish and were relatively poor predictors of lipid content and risk of mortality. The probability of mortality was most accurately predicted by percent lipid content. Therefore, we suggest that fisheries scientists consider using percent lipid content when evaluating the physiological status and risk of mortality due to starvation among juvenile rainbow trout.

Transactions of the American Fisheries Society↗

USGS2011

Application of a multistate model to estimate culvert effects on movement of small fishes

While it is widely acknowledged that culverted road-stream crossings may impede fish passage, effects of culverts on movement of nongame and small-bodied fishes have not been extensively studied and studies generally have not accounted for spatial variation in capture probabilities. We estimated probabilities for upstream and downstream movement of small (30-120 mm standard length) benthic and water column fishes across stream reaches with and without culverts at four road-stream crossings over a 4-6-week period. Movement and reach-specific capture probabilities were estimated using multistate capture-recapture models. Although none of the culverts were complete barriers to passage, only a bottomless-box culvert appeared to permit unrestricted upstream and downstream movements by benthic fishes based on model estimates of movement probabilities. At two box culverts that were perched above the water surface at base flow, observed movements were limited to water column fishes and to intervals when runoff from storm events raised water levels above the perched level. Only a single fish was observed to move through a partially embedded pipe culvert. Estimates for probabilities of movement over distances equal to at least the length of one culvert were low (e.g., generally ???0.03, estimated for 1-2-week intervals) and had wide 95% confidence intervals as a consequence of few observed movements to nonadjacent reaches. Estimates of capture probabilities varied among reaches by a factor of 2 to over 10, illustrating the importance of accounting for spatially variable capture rates when estimating movement probabilities with capture-recapture data. Longer-term studies are needed to evaluate temporal variability in stream fish passage at culverts (e.g., in relation to streamflow variability) and to thereby better quantify the degree of population fragmentation caused by road-stream crossings with culverts. ?? American Fisheries Society 2009.

Transactions of the American Fisheries Society↗

USGS2015

Precision of hard structures used to estimate age of mountain Whitefish ( Prosopium williamsoni )

The mountain whitefish ( Prosopium williamsoni ) is a widely distributed salmonid in western North America that has decreased in abundance over portions of its distribution due to anthropogenic disturbances. In this investigation, we examined precision of age estimates derived from scales, pectoral fin rays, and sagittal otoliths from 167 mountain whitefish. Otoliths and pectoral fin rays were mounted in epoxy and cross-sectioned before examination. Scales were pressed onto acetate slides and resulting impressions were examined. Between-reader precision (i.e., between 2 readers), between-reader variability, and reader confidence ratings were compared among hard structures. Coefficient of variation (CV) in age estimates was lowest and percentage of exact agreement (PA-0) was highest for scales (CV = 5.9; PA-0 = 70%) compared to pectoral fin rays (CV =11.0; PA-0 = 58%) and otoliths (CV = 12.3; PA-0 = 55%). Median confidence ratings were significantly different ( P ≤ 0.05) among all structures, with scales having the highest median confidence. Reader confidence decreased with fish age for scales and pectoral fin rays, but reader confidence increased with fish age for otoliths. In general, age estimates were more precise and reader confidence was higher for scales compared to pectoral fin rays and otoliths. This research will help fisheries biologists in selecting the most appropriate hard structure to use for future age and growth studies on mountain whitefish. In turn, selection of the most precise hard structure will lead to better estimates of dynamic rate functions.

Western North American Naturalist↗

USGS2010

Assessing the effects of catch and release regulations on a quality adfluvial brook trout population using a computer based age-structure model

Assessing the Effects of Catch-and-Release Regulations on a Brook Trout Population Using an Age-Structured Model: North American Journal of Fisheries Management: Vol 30, No 6  var _prum=[['id','54ff88bcabe53dc41d1004a5'],['mark','firstbyte',(new Date()).getTime()]];(function(){var s=document.getElementsByTagName('script')[0],p=document.createElement('script');p.async='async';p.src='//rum-static.pingdom.net/prum.min.js';s.parentNode.insertBefore(p,s);})(); (function (i, s, o, g, r, a, m) { i['GoogleAnalyticsObject'] = r; i[r] = i[r] || function () { (i[r].q = i[r].q || []).push(arguments) }, i[r].l = 1 * new Date(); a = s.createElement(o), m = s.getElementsByTagName(o)[0]; a.async = 1; a.src = g; m.parentNode.insertBefore(a, m) })(window, document, 'script', '//www.google-analytics.com/analytics.js', 'ga'); ga('create', 'UA-3062505-5' , 'auto' ); ga('set', 'dimension1', 'ujfm20'); ga('send', 'pageview'); As populations of wild brook trout Salvelinus fontinalis decline across the species' native range in North America, angling regulations such as fly-fishing only and catch and release are being used by management agencies to conserve fish while maintaining angling opportunities. Postrelease (hooking) mortality may significantly shift the age structure and size structure of populations. To assess the possible influence of catch-and-release fishing on brook trout population structure, we applied data from several sources to build a deterministic population model that included age-classes up to age 5. To assess the potential effect of fishing, we examined the changes in population density and age structure at varying levels of angler effort (0–400 angler-hours·ha −1 ·year −1 ) and hooking mortality rates (0–14%). Assuming a low (5%) hooking mortality rate, trophy brook trout density (ages 4 and 5) decreased by 50% at an angling intensity of 160 angler-hours·ha −1 ·year −1 . As angling effort increased, the proportion of older fish (ages 3–5) declined further. At very high levels of angling effort (>300 angler-hours·ha −1 ·year −1 ), age-4 and age-5 fish were eliminated from the population. Increases in postrelease mortality rates resulted in similar declines for older age-classes. The results of this simulation indicate that hooking mortality rates as might be common in catch-and-release fisheries may significantly shift the age structure of a population, thus reducing trophy angling potential.

North American Journal of Fisheries Management↗

USGS2018

Food‐web structure and ecosystem function in the Laurentian Great Lakes—Toward a conceptual model

The relationship between food‐web structure (i.e., trophic connections, including diet, trophic position, and habitat use, and the strength of these connections) and ecosystem functions (i.e., biological, geochemical, and physical processes in an ecosystem, including decomposition, production, nutrient cycling, and nutrient and energy flows among community members) determines how an ecosystem responds to perturbations, and thus is key to understanding the adaptive capacity of a system (i.e., ability to respond to perturbation without loss of essential functions). Given nearly ubiquitous changing environmental conditions and anthropogenic impacts on global lake ecosystems, understanding the adaptive capacity of food webs supporting important resources, such as commercial, recreational, and subsistence fisheries, is vital to ecological and economic stability. Herein, we describe a conceptual framework that can be used to explore food‐web structure and associated ecosystem functions in large lakes. We define three previously recognised broad habitat compartments that constitute large lake food webs (nearshore, pelagic, and profundal). We then consider, at three levels, how energy and nutrients flow: (a) into each basal resource compartment; (b) within each compartment; and (c) among multiple compartments (coupling). Flexible shifts in food‐web structures (e.g., via consumers altering their diet or habitat) that sustain these flows in the face of perturbations provide evidence for adaptive capacity. We demonstrate the conceptual framework through a synthesis of food‐web structure and ecosystem function in the Laurentian Great Lakes, with emphasis on the upper trophic levels (i.e., fishes). Our synthesis showed evidence of notable adaptive capacity. For example, fishes increased benthic coupling in response to invasion by mussels and round gobies. However, we also found evidence of loss of adaptive capacity through species extirpations (e.g., widespread collapse in the abundance and diversity of ciscoes, Coregonus spp., except in Lake Superior). In large freshwater lakes, fishery managers have traditionally taken a top‐down approach, focusing on stocking and harvest policy. By contrast, water quality managers have focused on nutrient effects on chemical composition and lower trophic levels of the ecosystem. The synthesised conceptual model provides resource managers a tool to more systematically interpret how lower food‐web dynamics influence harvestable fish populations, and vice versa, and to act accordingly such that sustainable resource practices can be achieved. We identify key gaps in knowledge that impede a fuller understanding of the adaptive capacities of large lakes. In general, we found a greater uncertainty in our understanding of processes influencing energy and nutrient flow within and among habitats than flows into the system.

Great Lakes↗

USGS2021

A review of factors affecting PIT tag detection using mobile arrays and use of mobile antennas to detect PIT-tagged suckers in a wadeable Ozark stream

Advantages of passive integrated transponder (PIT) tags are their small size, longevity, and low-cost compared to other tags. PIT tags are often used in fisheries to study movement patterns, survival, or estimate population size. However, PIT tags are limited by their short detection distance. Mobile PIT antennas may increase the utility of PIT tags in fisheries. In this study, we synthesize the current detection efficiency literature on mobile PIT antennas, determine factors influencing PIT-tag detection probability and efficiency for a raft-mounted mobile antenna, and summarize techniques used to increase observations of PIT-tagged fishes with raft-mounted mobile antennas in a wadable stream. Our literature review indicated tag size and orientation were the most-important factors affecting detection probabilities; however, our antenna was primarily influenced by water depth of the tag and distance from the antenna. Detection efficiency was influenced by discharge, turbidity, and sample date. Tracking methods that include targeting key habitats (e.g., rootwads) and using natural features to congregated tagged fishes (e.g., riffles or pinch points) may increase detection efficiency in wadable streams. This is the first formal review of factors affecting mobile PIT antenna detection efficiency. The published literature, combined with our study results, indicate several factors need to be considered prior to mobile PIT antenna tracking.

Arkansas, Oklahomas↗

USGS2025

Non-native prey availability and over-compensatory density dependence drive population dynamics of a native fish predator

Understanding the factors that regulate population dynamics is crucial for conserving imperiled species. Bull trout ( Salvelinus confluentus ), a piscivorous salmonid and one of North America's most threatened cold-water species, has declined significantly due to habitat loss, overfishing, invasive species, and climate change. While recovery efforts have primarily targeted these threats, the role of prey availability in influencing bull trout population dynamics under multiple stressors remains poorly understood. Using a stage-based integrated population model, we quantified the effects of non-native prey availability (kokanee; Oncorhynchus nerka ), angling pressure, climatic variation, and density-dependent processes on bull trout population dynamics in Lake Koocanusa, a transboundary reservoir and river system (United States and Canada), over a 40-year period (1980–2023). Our results show that bull trout populations are regulated by density-dependent processes, including over-compensation in sub-adult recruitment and reduced adult survival at high densities. Increased kokanee biomass and restricted harvest significantly enhanced bull trout survival and abundance, whereas reduced water availability had a limited negative effect on sub-adult production. Model simulations indicate that as kokanee biomass availability increases, the number of bull trout that can be sustainably harvested also increases. In fact, a modest annual fishery (300 individuals) can be sustained, especially under moderate to high kokanee biomass conditions. These results underscore the importance of prey availability, including non-native species, in supporting bull trout populations. Effective management of threatened apex fish predators like bull trout requires addressing the complex interplay between environmental threats, prey dynamics, and density-dependent mechanisms across all life stages.

British Columbia, Montana↗

USGS2013

A novel approach to surveying sturgeon using side-scan sonar and occupancy modeling

Technological advances represent opportunities to enhance and supplement traditional fisheries sampling approaches. One example with growing importance for fisheries research is hydroacoustic technologies such as side-scan sonar. Advantages of side-scan sonar over traditional techniques include the ability to sample large areas efficiently and the potential to survey fish without physical handling-important for species of conservation concern, such as endangered sturgeons. Our objectives were to design an efficient survey methodology for sampling Atlantic Sturgeon Acipenser oxyrinchus by using side-scan sonar and to developmethods for analyzing these data. In North Carolina and South Carolina, we surveyed six rivers thought to contain varying abundances of sturgeon by using a combination of side-scan sonar, telemetry, and video cameras (i.e., to sample jumping sturgeon). Lower reaches of each river near the saltwater-freshwater interface were surveyed on three occasions (generally successive days), and we used occupancy modeling to analyze these data.We were able to detect sturgeon in five of six rivers by using these methods. Side-scan sonar was effective in detecting sturgeon, with estimated gear-specific detection probabilities ranging from 0.2 to 0.5 and river-specific occupancy estimates (per 2-km river segment) ranging from 0.0 to 0.8. Future extensions of this occupancy modeling framework will involve the use of side-scan sonar data to assess sturgeon habitat and abundance in different river systems.

North Carolina, South Carolina↗

USGS1949

The age, growth, and distribution of the longjaw cisco, Leucichthys alpenae Koelz, in Lake Michigan

The longjaw (Leucichthys alpenae) was found at all of the 109 stations fished in the open lake during 1930–1932 and at 29 of the 32 stations in Green Bay in 1930 and 1932. Koelz (1929) found the longjaw at 35 localities, 33 of which were different from those fished in 1930–1932. The species was most abundant in water with a depth of less than 70 fathoms, but was found as deep as 97 fathoms. The longjaw was estimated to be about 4 1/3 times as abundant along the east shore of southern Lake Michigan as along the west shore in 1930 and 1931. The abundance along the east shore in 1930–1931 was estimated to be approximately equal to that in northern Lake Michigan in 1932. The best explanation for the relative scarcity of L. alpenae along the west shore is that a more intensive fishery, with smaller sizes of mesh, was operating on a separate population. The length distribution of 6,954 specimens taken in 1930–1932 revealed little difference in frequencies between the sexes, the samples taken in each of the years 1930 and 1931, or the fish taken on the two shores of the southern region. The individuals caught in 1932 from northern Lake Michigan averaged 12.5 inches, total length, and were from 1.0 to 1.3 inches longer than fish taken by the same sizes of mesh from the southern area in 1930–1931. Of the 378 longjaws whose ages were determined, 320 were taken during the summer of 1923 in northeastern Lake Michigan, and 58 were secured off Grand Haven, Michigan, in November 1928. The age groups represented ranged from II to IX. Age-group IV dominated in the 1923 samples making up 53.8 percent of the total, and age-groups III and V with 20.9 and 10.6 percent, respectively, were the next best represented groups. The III group dominated the 1928 collection with 55.2 percent of the total, and age-groups IV and II, that were represented by 31.0 and 12.1 percent, respectively, were the only other well represented groups. The sexes grew at approximately the same rate. A total length of 11.1 inches and a weight of 6.4 ounces were reached at the end of 4 years of growth by the longjaws in northeastern Lake Michigan. The fish from Grand Haven averaged 11.0 inches, total length, and 6.1 ounces at the end of 4 years. Growth in length was most rapid during the first year and decreased continuously thereafter through the fourth year (fifth year in 1928). The increments in length of the 1923 fish during the fourth through the eighth years were approximately the same. Growth in weight of the fish taken in 1923 was computed to be most rapid following the fifth year of life. Growth compensation occurred among the longjaws of Lake Michigan. The major part of the annual growth in length had taken place before June 15, 1923. Although the empirical data on the length-weight relationship of 5,314 fish failed to fall along a simple curve, it is believed that the following equation is the one best suited to computing the weight of the longjaw: W = 0.96288 × 10 −5 L 3.06060 . The coefficient of condition (K) of all longjaws increased as the standard length increased to 194 millimeters. The values then remained high up to 225 millimeters but decreased progressively until the fish reached a length of 265 millimeters. The coefficient changed little at fish lengths of 265 to 284 but began to increase again at 285 millimeters. Condition was best in 1931 and poorest in 1932. The individuals of both sexes were in the poorest condition during some month previous to August each year. Although the females were somewhat heavier in relation to their length than the males in practically all months, the weighted averages of K for all males and all females were almost identical (1.30 for the males and 1.31 for the females). The sex ratio was determined from 7,457 individuals taken in 1930–1932 and 373 of the 1923 and 1928 specimens whose ages were determined. The percentage of females was relatively low in May 1931 and relatively high in October, but in the other months it remained more or less constant. In 1932 the females tended to become relatively less abundant in each month from April through September. There was little difference between the relative abundance of the sexes in 1930 and 1931 (72.4 percent females in 1930 and 67.5 percent in 1931). The consistently slightly higher percentage of females each month in 1932 (average of 80.6) probably represents a difference between populations. The relative abundance of the males decreased as the age increased. A natural differential mortality is suggested as the cause for the more rapid disappearance of the males. Females may contain ripe eggs as early as July 9, and some females may spawn as early as October 16 despite the fact that the spawning season is in November.

Transactions of the American Fisheries Society↗

USGS1970

Walleye fishery of Lake Erie in 1943-62 with emphasis on contributions of the 1942-61 year-classes

The commercial fishery for walleyes ( Stizostedion vitreum vitreum ) in Lake Erie virtually collapsed in the late 1950's. The extreme decline in production was attributed primarily to a succession of weak year-classes, caused by habitat deterioration (increased water temperatures, enrichment, and pollution) in western Lake Erie. Unusually high fishing intensity and high yields of walleyes in the mid-1950's contributed to the collapse.Annual lakewide production of walleyes dropped from a record high of 15 million lb in 1956 to a record low of 717,000&ensp;lb in 1962. Canadian catches exceeded those of the United States only during the high production years of 1956–58; U.S. fishermen took 71% of the total catch in 1915–62.On the basis of the numbers of fish of the various year-classes in the fall trapnet samples at Sandusky, Ohio, in 1943–62, all but one of the 1942–52 year-classes were above average strength, and all but one of the 1953–61 year-classes were below average. Fish of the 1953–61 year-classes grew much faster than those of the 1942–52 year-classes. The strong 1948 year-class was followed by a series of progressively weaker year-classes until 1958; year-class strengths remained low through 1962.

Journal of the Fisheries Research Board of Canada↗

USGS2026

Gerrard strain Rainbow Trout are not piscivorous in a shallow, polymictic reservoir

Objective Georgetown Lake (Montana, USA) is renowned for its multispecies salmonid fishery. Although many anglers target kokanee Oncorhynchus nerka in Georgetown Lake, the body length of kokanee has typically been considered unsatisfactory. To reduce the density of kokanee and increase the average size, Montana Fish, Wildlife & Parks began stocking the piscivorous Gerrard strain of Rainbow Trout O. mykiss (hereafter “Gerrard”) in 2015 to consume kokanee. In 2020, preliminary evidence suggested that the average length of kokanee greater than 200 mm increased by almost 40 mm. Methods To assess the efficacy of biocontrol through the introduction of a piscivore to predate on kokanee, we examined the diet composition of all potential predators (three strains of Rainbow Trout and Brook Trout Salvelinus fontinalis ) to determine the amount of predation on kokanee and to understand the feeding ecology of all potential predators. Results There was little evidence of piscivory in any predator and no evidence of Gerrards consuming kokanee. Gerrards exhibited a generalist feeding strategy, and there was dietary overlap and no difference in trophic position among Gerrards and other predators. Conclusions From a biological-control perspective, there is no benefit in continuing to stock Gerrards to reduce kokanee densities in Georgetown Lake. These findings underscore the challenge of predicting predator–prey relationships, as diet plasticity can lead to unexpected dynamics based on resource availability and habitat structure within aquatic ecosystems, highlighting the importance of evaluating management interventions, such as biocontrols, in different ecosystems.

Montana↗

USGS2018

Lower lethal temperatures for nonnative freshwater fishes in Everglades National Park, Florida

Temperature is an important factor that shapes biogeography and species composition. In southern Florida, the tolerance of nonnative freshwater fishes to low temperatures is a critical factor in delineating their geographic spread. In this study, we provide empirical information on experimentally derived low-temperature tolerance limits of Banded Cichlid Heros severus and Spotfin Spiny Eel Macrognathus siamensis, two nonnative Everglades fishes that were lacking data, and African Jewelfish Hemichromis letourneuxi and Mayan Cichlid Cichlasoma urophthalmus, species for which previous results were derived from studies with small sample sizes. We also provide a literature review summarizing the current state of knowledge of low-temperature tolerances for all 17 nonnative freshwater fishes that have been found in Everglades National Park. Mean lower lethal temperature tolerances ranged from 4°C (Orinoco Sailfin Catfish Pterygoplichthys multiradiatus) to 16.1°C (Butterfly Peacock Bass Cichla ocellaris). These low-temperature limits may inform the understanding of the ecological role or influence of nonnative fishes and may lead to potential management opportunities and applications.

Florida↗

USGS2019

Understanding fish assemblage structure in lentic ecosystems: Relative effects of abiotic factors and management legacies

We investigated associations of fish assemblages and habitat characteristics (e.g., morphology and water chemistry) from 45 natural lakes and reservoirs in Iowa to determine whether species or trophic guild composition and environmental correlations were concordant between waterbodies of different origins. Overall, fish assemblage composition between natural lakes and reservoirs was consistently dissimilar based on a permutational multivariate ANOVA. Species composition from nonmetric multidimensional scaling ordinations for reservoirs was correlated with a variety of limnological and physical characteristics, whereas species composition and trophic composition of natural lakes were weakly associated with habitat characteristics. Species richness was positively related to waterbody and watershed size for reservoirs but not for natural lakes. Conversely, species richness was negatively correlated with increasing eutrophic conditions in natural lakes but not in reservoirs. Overall, distinct differences in assemblage composition were observed between natural and artificial lentic ecosystems and may have resulted from underlying differences in limnological, physical, and anthropogenic influences between systems. Dissimilar management legacies between waterbody types, such as limited or no stocking of nonrecreationally important species and the use of piscicides, may have additionally had overriding effects on the observed assemblage–environmental relationships. For instance, lower trophic richness and species richness in reservoirs appeared to have resulted from replacement of a diversity of small-bodied native species by relatively few commonly stocked sport fishes. Our results emphasize the need to consider waterbody origin and the potential influence of historical or current management strategies on fish assemblage characterization and subsequent inferences made from environmental correlations.

Iowa↗

USGS2019

Nonlethal detection of Asian fish tapeworm in the federally-endangered Humpback Chub using a molecular screening tool

Optimal spawning habitat of federally endangered Humpback Chub Gila cypha exists within the Little Colorado River; however, temperatures in the Little Colorado River are also ideal for proliferation of the invasive pathogenic Asian fish tapeworm Schyzocotyle acheilognathi . The current standard for positive identification of the parasite is necropsy and visual examination of the gut via microscopy, a methodology undesirable for assessing infection in endangered fishes. A swab taken at the rectum of the fish and analyzed using a novel DNA primer targeting the cestode cytochrome oxidase I subunit mtDNA gene region offers a convenient nonlethal sampling tool. To validate the nonlethal methodology, primer sensitivity (51.9%) and specificity (79.5%) were calculated by exposing captive fish to the parasite and comparing results using the lethal standard method (i.e., visual examination). Subsequently, we utilized this nonlethal methodology to address prevalence of infection and infection frequency across a range of size-classes in a wild population of Humpback Chub and addressed possible patterns and mechanisms of infection in the Little Colorado River. When wild Humpback Chub were screened for infection prevalence in spring 2015 (21.4%, n = 140) and fall 2015 (6.6%, n = 258), the relative frequency of infection was highest in juveniles and subadult fish (200–300 mm). Elevated levels of infection near the major spawning grounds of Humpback Chub in the Little Colorado River promote parasitic infection, which may continue to persist without treatment or actions to control infections. We demonstrated that rectal swabs, in conjunction with PCR and primer-specific identification, offer a time-efficient nonlethal method to detect infection of Asian fish tapeworm in an endangered fish.

Transactions of the American Fisheries Society↗

USGS2022

Assessment of native fish passage through Brandon Road Lock and Dam, Des Plaines River, Illinois, using fin ray microchemistry

This study examined evidence of native fish passage through Brandon Road Lock and Dam (BRLD) on the Des Plaines River, Illinois, in light of proposed modifications to prevent the upstream passage of invasive carps. Direct evidence of upstream passage by native fishes at BRLD is lacking and could help to inform assessment of the impacts of barrier technology installation. Fin ray microchemistry was used to assess upstream BRLD passage in the native taxa Centrarchidae, Catostomidae, Ictaluridae, and Lepisosteidae. The fin ray edge strontium : calcium ratio (Sr:Ca) of fish sampled from the Des Plaines River upstream of BRLD and in rivers downstream of BRLD was used to characterize ranges of river-specific fin ray Sr:Ca for each taxon. These were applied to Sr:Ca data along a transect from fin ray core to edge to infer the environmental history of individual fish that were captured upstream from BRLD and to estimate the proportion of fish that had passed upstream through BRLD. Depending on the taxon, 6–37% of individuals sampled upstream from BRLD exhibited fin ray Sr:Ca indicating prior residency in rivers downstream of BRLD and therefore upstream passage through BRLD. Upstream passage was indeterminate for 19–91% of individuals in each taxon due to uncertainty in environmental history inferred from fin ray Sr:Ca. These results provide the first definitive evidence of upstream native fish passage at BRLD and suggest that the installation of barrier technology could have an impact on native fish.

Illinois↗

USGS2010

Traveling around Cape Horn: Otolith chemistry reveals a mixed stock of Patagonian hoki with separate Atlantic and Pacific spawning grounds

Trace element fingerprints of edge and core regions in otoliths from 260 specimens of Patagonian hoki, Macruronus magellanicus L??nnberg, 1907, were analyzed by LA-ICPMS to reveal whether this species forms one or more population units (stocks) in the Southern Oceans. Fish were caught on their spawning grounds in Chile and feeding grounds in Chile and the Falkland Islands. Univariate and multivariate analyses of trace element concentrations in the otolith edges, which relate to the adult life of fish, could not distinguish between Atlantic (Falkland) and Pacific (Chile) hoki. Cluster analyses of element concentrations in the otolith edges produced three different clusters in all sample areas indicating high mixture of the stocks. Cluster analysis of trace element concentrations in the otolith cores, relating to juvenile and larval life stages, produced two separate clusters mainly distinguished by 137 Ba concentrations. The results suggest that Patagonian hoki is a highly mixed fish stock with at least two spawning grounds around South America. ?? 2009 Elsevier B.V.

Fisheries Research↗

USGS2012

Effects of activity and energy budget balancing algorithm on laboratory performance of a fish bioenergetics model

We evaluated the performance of the Wisconsin bioenergetics model for lake trout Salvelinus namaycush that were fed ad libitum in laboratory tanks under regimes of low activity and high activity. In addition, we compared model performance under two different model algorithms: (1) balancing the lake trout energy budget on day t based on lake trout energy density on day t and (2) balancing the lake trout energy budget on day t based on lake trout energy density on day t + 1. Results indicated that the model significantly underestimated consumption for both inactive and active lake trout when algorithm 1 was used and that the degree of underestimation was similar for the two activity levels. In contrast, model performance substantially improved when using algorithm 2, as no detectable bias was found in model predictions of consumption for inactive fish and only a slight degree of overestimation was detected for active fish. The energy budget was accurately balanced by using algorithm 2 but not by using algorithm 1. Based on the results of this study, we recommend the use of algorithm 2 to estimate food consumption by fish in the field. Our study results highlight the importance of accurately accounting for changes in fish energy density when balancing the energy budget; furthermore, these results have implications for the science of evaluating fish bioenergetics model performance and for more accurate estimation of food consumption by fish in the field when fish energy density undergoes relatively rapid changes.

Transactions of the American Fisheries Society↗

USGS2013

Fish assemblages in borrow-pit lakes of the Lower Mississippi River

Borrow-pit lakes encompass about a third of the lentic water habitats (by area) in the active floodplain of the Lower Mississippi River, yet little is known about their fish assemblages. We investigated whether fish assemblages supported by borrow-pit lakes resembled those in oxbow lakes to help place the ecological relevance of borrow-pit lakes in context with that of natural floodplain lakes. In all, we collected 75 fish species, including 65 species in eight borrow-pit lakes, 52 species in four riverside oxbow lakes, and 44 species in eight landside oxbow lakes. Significant differences in several species richness metrics were evident between borrow-pit lakes and landside oxbow lakes but not between borrow-pit lakes and riverside oxbow lakes. All three lake types differed in fish assemblage composition. Borrow-pit lakes and riverside oxbow lakes tended to include a greater representation of fish species that require access to diverse environments, including lentic, lotic, and palustrine habitats; fish assemblages in landside oxbow lakes included a higher representation of lacustrine species. None of the fish species collected in borrow-pit lakes was federally listed as threatened or endangered, but several were listed as species of special concern by state governments in the region, suggesting that borrow-pit lakes provide habitat for sensitive riverine and wetland fish species. Differences in fish assemblages among borrow-pit lakes were linked to engineered morphologic features, suggesting that diversity in engineering can contribute to diversity in fish assemblages; however, more research is needed to match engineering designs with fish assemblage structures that best meet conservation needs.

Lower Mississippi River↗