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USGS2014

Recent population size, trends, and limiting factors for the double-crested Cormorant in Western North America

The status of the double-crested cormorant ( Phalacrocorax auritus ) in western North America was last evaluated during 1987–2003. In the interim, concern has grown over the potential impact of predation by double-crested cormorants on juvenile salmonids ( Oncorhynchus spp.), particularly in the Columbia Basin and along the Pacific coast where some salmonids are listed for protection under the United States Endangered Species Act. Recent re-evaluations of double-crested cormorant management at the local, flyway, and federal level warrant further examination of the current population size and trends in western North America. We collected colony size data for the western population (British Columbia, Washington, Oregon, Idaho, California, Nevada, Utah, Arizona, and the portions of Montana, Wyoming, Colorado and New Mexico west of the Continental Divide) by conducting aircraft-, boat-, or ground-based surveys and by cooperating with government agencies, universities, and non-profit organizations. In 2009, we estimated approximately 31,200 breeding pairs in the western population. We estimated that cormorant numbers in the Pacific Region (British Columbia, Washington, Oregon, and California) increased 72% from 1987–1992 to circa 2009. Based on the best available data for this period, the average annual growth rate (λ) of the number of breeding birds in the Pacific Region was 1.03, versus 1.07 for the population east of the Continental Divide during recent decades. Most of the increase in the Pacific Region can be attributed to an increase in the size of the nesting colony on East Sand Island in the Columbia River estuary, which accounts for about 39% of all breeding pairs in the western population and is the largest known breeding colony for the species (12,087 breeding pairs estimated in 2009). In contrast, numbers of breeding pairs estimated in coastal British Columbia and Washington have declined by approximately 66% during this same period. Disturbance at breeding colonies by bald eagles ( Haliaeetus leucocephalus ) and humans are likely limiting factors on the growth of the western population at present. Because of differences in biology and management, the western population of double-crested cormorants warrants consideration as a separate management unit from the population east of the Continental Divide.

Journal of Wildlife Management↗

USGS2021

Evaluating fish rescue as a drought adaptation strategy using a life cycle modeling approach for imperiled coho salmon

Projected intensification of drought as a result of climate change may reduce the capacity of streams to rear fish, exacerbating the challenge of recovering salmonid populations listed under the Endangered Species Act. Without management intervention, some stocks will likely go extinct as stream drying and fragmentation reduce juvenile survival to unsustainable levels. To offset drought‐related mortality, fish rescue programs have proliferated, whereby juvenile salmonids are captured and transferred to off‐site rearing facilities. However, the efficacy of this potential conservation tool remains poorly understood. We developed a life cycle model to examine the implications of fish rescue on the abundance of Coho Salmon Oncorhynchus kisutch across serial life stages. The simulation model examines scenarios with varying quantities of rescued fish, time in captivity, drought severity, and reduced smolt‐to‐adult return rates. Our results indicate that fish rescue can increase the abundance of adults and lower extinction risk, particularly for fish held in captivity for a full year. However, fish rescue can also decrease the abundance of adults and increase extinction risk if fish are held only for summer and there is limited winter habitat. We found that when fish rescue did increase returns, it functioned more like a stock enhancement program than a drought mitigation tool and it would likely lead to consecutive generations of captive rearing, which has been shown to have negative effects on fitness. We translated our model into an R Shiny application ( https://shiny.wdfw‐fish.us/CohoPopulationDynamics/ ) that allows users to explore how fish rescue affects Coho Salmon population dynamics through customized parameterization of the model to represent different systems or different assumptions about the effects of fish rescue.

North American Journal of Fisheries Management↗

USGS2021

Evaluation of remote site incubators to incubate wild- and hatchery-origin Westslope Cutthroat Trout embryos

Fish managers must weigh trade-offs among cost, speed, efficiency, and ecological adaptation when deciding how to translocate native salmonids to either establish or genetically augment populations. Remote site incubators (RSIs) appear to be a reasonable strategy, but large-scale evaluations of this method have been limited. We used 129 RSIs to incubate >35,700 eyed embryos of Westslope Cutthroat Trout Oncorhynchus clarkii lewisi at eight sites within the upper 30 km of the Cherry Creek basin (Madison River, Montana) from 2007 to 2010, after using piscicides to remove all fish. We obtained gametes from 258 parental-pair crosses (164 females and 258 males) from four wild populations and two hatchery broods. All embryos were incubated to the eyed stage in two hatcheries prior to placing them in RSIs. Green-to-eyed egg survivals were higher for progeny of wild-spawned adults (median, 91.0%; 95% CI, 88.7–93.7%) than for progeny of hatchery-spawned adults (median, 81.7%; 95% CI, 74.9–88.4%), and this difference was highly significant ( P < 0.01). Over 26,500 fry were counted leaving RSIs. Median embryo-to-fry survival was 75.6% (95% CI, 72.2–79.0%). Fry exited individual RSIs from 8 to 45 d after embryo translocation. Fry survivals differed among years and sites, and year was more important than site in explaining variation in survival. The success of RSI fry introductions was confirmed by annual monitoring of fish abundance, which indicated that abundances of Westslope Cutthroat Trout 5 to 9 years after RSI introductions were equal to or higher than abundances of nonnative salmonids prior to their removal using piscicides.

Montana↗

USGS2022

Trout responses to stocking rates and river discharge within a southeast U.S. hydropeaking tailwater

Freshwater fish populations often exist in systems characterized by novel ecological processes resulting from human alteration. Salmonid populations embedded within coldwater sections of warmwater rivers are spatially constrained by habitat availability. Tailwater fish contend with fluctuating river discharges and density-dependent processes associated with fish stocking and exploitation. Salmonid populations sustained through stocking versus natural reproduction may respond differently to changes in hydrologic patterns (e.g., hydropeaking) as well as declines in fish abundance. We assessed differences between stocked (Rainbow Trout Oncorhynchus mykiss ) and naturalized (Brown Trout Salmo trutta ) trout populations in Greers Ferry tailwater, Arkansas, regarding (1) spatial and temporal patterns of mean length, electrofishing catch rates, and relative condition following reduced number of stocked Rainbow Trout and (2) evidence that hydrologic characteristics and fish stocking intensity influenced relative condition. A 56% reduction in Rainbow Trout stocking did not result in systemwide change in mean length or relative abundance for Rainbow Trout or Brown Trout over the 16-year study period. Hydrologic variability, where river discharge spanned both reduced and elevated levels, positively influenced condition of both Rainbow Trout and Brown Trout. Assessment of survival of stocked Rainbow Trout may aid in further refining the timing and amount of stocking needed to sustain the population at a desired abundance. Further, assessing the influence of stocking fewer but perhaps larger (in terms of mean length) fish to meet management goals may be warranted. The persistent differences in relative abundance among river sections can inform management actions directed at Brown Trout, including harvest regulations. Such regulations may aid in reaching desired management goals, including abundance and mean length targets not observed after reduced stocking.

Arkansas↗

USGS2022

Temporal variation in capture efficiency underrepresents spring out-migrating Bull Trout in a trap-and-haul program

Trap-and-haul programs can maintain connection among habitats for migratory salmonids in fragmented systems. To conserve diversity within and among life history strategies, downstream trap and transport of juvenile salmonids could ideally mimic the natural, underlying out-migration dynamics of the population. A two-way trap-and-haul program is implemented in the lower Clark Fork River, Montana, to conserve adfluvial Bull Trout Salvelinus confluentus. We used PIT technology to assess whether downstream trapping efforts are effectively capturing variation in the out-migration dynamics of juvenile Bull Trout in Graves Creek, a key spawning and rearing tributary in the system. We tagged 821 juvenile Bull Trout in Graves Creek and used these tagged Bull Trout in conjunction with stationary PIT antennas to monitor out-migration and evaluate efficiency of the downstream trapping program. Capture efficiency in Graves Creek varied substantially from autumn to spring, with 89–96% of autumn out-migrating Bull Trout captured and 5–10% of spring out-migrating Bull Trout captured. Overall, we found that Bull Trout transported during the autumn out-migration periods generally reflect the natural out-migration dynamics of the population; however, Bull Trout that out-migrate in the spring are currently underrepresented in the downstream transport program. By understanding the underlying out-migration dynamics of the Bull Trout population in Graves Creek, management of the downstream trapping efforts can focus on minimizing potential selection for or against out-migrants based on timing and age at out-migration. Minimizing selection will conserve variation within the adfluvial life history strategy and therefore maximize resilience of the adfluvial Bull Trout populations.

Idaho, Montana↗

USGS2023

Estimates of predator densities using mobile DIDSON surveys: Implications for survival of Central Valley Chinook Salmon

The Sacramento–San Joaquin Delta (hereafter, “the Delta”) is one of the estuaries with the most invasive species in the world, and nonnative predators may be a major factor in the observed decline of Central Valley Chinook Salmon Oncorhynchus tshawytscha over recent decades. In order for managers to take actions that might reduce predation-related mortality for these ecologically, culturally, and economically valuable fish, it is important to understand the factors influencing the distribution and abundance of piscivores in the Delta. In this study, we used a dual-frequency identification sonar (i.e., DIDSON) to conduct mobile surveys to quantify the abundances of piscivores in the Delta. We then used these data to identify the habitat features that are correlated with the abundance of piscivores. Prior to conducting the surveys, we used DIDSON data from captured fish to develop an algorithm to distinguish piscivores from nonpiscivores with high confidence (98% accuracy). A generalized linear mixed-effects model fit to these survey data indicated that predator abundances were most associated with areas of increased submerged aquatic vegetation patches, and channels that are straighter, with increased bathymetric complexity. When applied to the entire survey area, this model was successfully able to predict known areas of high predator densities. These results indicate that one approach to reduce predator densities in key locations throughout the Delta, and improve juvenile salmonid outmigration survival, is to reduce the extent of invasive submerged aquatic vegetation. Because experimental predator removals have been largely ineffective in the Delta, efforts to manipulate habitat to discourage nonnative predator recruitment and favor native species recruitment may provide a more effective solution to improve salmonid survival rates.

California↗

USGS2023

Biotic and abiotic factors affecting short-term survival of two age-0 Rainbow Trout strains in Colorado streams

Both biotic and abiotic factors can influence the survival and growth of age-0 salmonids. Diseases, such as whirling disease, can also affect salmonid demographics and population dynamics. Here, we conducted a supplementary analysis and evaluated specific stream characteristics that may have been responsible for the differences in growth and survival of two whirling disease resistant Rainbow Trout Oncorhynchus mykiss strains observed by Avila et al. (2018). We used regression modeling to analyze the influence of the biotic and abiotic characteristics of nine streams on the short-term apparent survival and growth of two Rainbow Trout strains, 5,000 German Rainbow Trout and 5,000 German Rainbow Trout × Colorado River Rainbow Trout in each stream. Akaike's information criterion (AIC c ) model selection was used to identify the factors that most affected short-term survival and growth. Average stream temperature had the largest (positive) effect, β temp = 0.060, on short-term survival. Rainbow Trout strain, average stream temperature (β temp = 1.55), competitor biomass (β competitor biomass = −0.002), and predator number (β predator number = 0.01) additively affected short-term growth. Our results indicate that both biotic and abiotic factors are important short-term determinants of Rainbow Trout poststocking performance and may account for the differences in survival and growth that we observed among stocking locations.

North American Journal of Fisheries Management↗

USGS2024

A genetic assessment of natural barriers for isolating a habitat network proposed for Greenback Cutthroat Trout reintroduction

Objective: Native inland trout conservation efforts rely on physical barriers to exclude nonnative salmonids from target habitats. We used genetic techniques to evaluate a series of natural waterfalls for their potential to serve as barriers to prevent nonnative salmonids from entering a proposed reintroduction area for federally threatened Greenback Cutthroat Trout Oncorhynchus virginalis stomias . Methods: Genetic samples were collected from nonnative Brook Trout Salvelinus fontinalis at 11 sampling reaches above and below natural waterfalls (height: ~1–3 m under base flow conditions) along a 33-km segment of Colorado's upper Cache la Poudre River near the outflow of the proposed reintroduction area. To evaluate whether upstream movement of Brook Trout is restricted by any of these waterfalls, we characterized longitudinal trends in genetic diversity along the river corridor and examined patterns of genetic differentiation and population structure in relation to waterfall locations using a panel of microsatellites. Result: We found no evidence that the waterfalls served as complete movement barriers for nonnative Brook Trout based on genetic clustering analyses, estimates of population differentiation, and longitudinal genetic patterns. Our multilocus assessment did not identify alleles restricted to downstream reaches, and the river segment was genetically homogenized. Conclusion: Our evaluation suggests that the existing waterfalls do not fully prevent upstream movement by nonnative Brook Trout, and thus barrier modification would be needed to establish an isolated Greenback Cutthroat Trout population in the proposed wilderness area.

Colorado↗

USGS2024

Food habits of nonnative Walleyes in Lake Pend Oreille, Idaho

Objective Walleye Sander vitreus is an important species that has been widely introduced outside of its native distribution. The goal of this study was to assess the effects of an established Walleye population in the Lake Pend Oreille (LPO) system, Idaho. Methods Food habits of Walleyes were described using stomach contents and stable isotopes (δ 15 N, δ 13 C). Trophic structure of the LPO system's food web was identified using stable isotopes. Annual consumption by Walleyes of important prey items was estimated using a bioenergetics model. Result Walleyes consumed a diversity of prey items, including macroinvertebrates and fishes. Kokanee Oncorhynchus nerka , the most frequently consumed prey item, occurred in 23% of all Walleye diets. Combined, native cyprinids and catostomids occurred in 31% of all Walleye stomachs. Select taxa (e.g., native cyprinids, kokanee) were consistently consumed by Walleyes across seasons, regions, and cohorts, whereas other taxa (e.g., Westslope Cutthroat Trout O. lewisi , Smallmouth Bass Micropterus dolomieu ) were consumed inconsistently. Stable isotope analysis suggested that Walleyes occupied similar trophic positions as other top‐level piscivores in the system . As Walleye age increased, δ 15 N increased and δ 13 C decreased, indicating increased consumption of pelagic prey resources and prey at higher trophic positions. The estimated biomass of kokanee consumed annually by Walleyes was 27,121 kg (95% confidence interval = 9178–61,603). Comparatively, native cyprinids represented about 46% of the total biomass of kokanee consumed by Walleyes, whereas native catostomids represented about 11% and native salmonids represented about 15% of the total biomass of kokanee consumed by Walleyes. Conclusion This study revealed that Walleyes consumed various fishes across the LPO system. Although kokanee were the most frequently consumed prey item, native cyprinids and catostomids (combined) occurred at similar proportions. This study contributes to our growing knowledge of the effects of nonnative Walleyes on important salmonids and native fishes in western systems.

Idaho↗

USGS2006

Evaluation of energy expenditure in adult spring Chinook salmon migrating upstream in the Columbia River Basin: an assessment based on sequential proximate analysis

The upstream migration of adult anadromous salmonids in the Columbia River Basin (CRB) has been dramatically altered and fish may be experiencing energetically costly delays at dams. To explore this notion, we estimated the energetic costs of migration and reproduction of Yakima River-bound spring Chinook salmon Oncorhynchus tshawytscha using a sequential analysis of their proximate composition (i.e., percent water, fat, protein, and ash). Tissues (muscle, viscera, and gonad) were sampled from fish near the start of their migration (Bonneville Dam), at a mid point (Roza Dam, 510 km upstream from Bonneville Dam) and from fresh carcasses on the spawning grounds (about 100 km above Roza Dam). At Bonneville Dam, the energy reserves of these fish were remarkably high, primarily due to the high percentage of fat in the muscle (18-20%; energy content over 11 kJ g-1). The median travel time for fish from Bonneville to Roza Dam was 27 d and ranged from 18 to 42 d. Fish lost from 6 to 17% of their energy density in muscle, depending on travel time. On average, fish taking a relatively long time for migration between dams used from 5 to 8% more energy from the muscle than faster fish. From the time they passed Bonneville Dam to death, these fish, depending on gender, used 95-99% of their muscle and 73-86% of their viscera lipid stores. Also, both sexes used about 32% of their muscular and very little of their visceral protein stores. However, we were unable to relate energy use and reproductive success to migration history. Our results suggest a possible influence of the CRB hydroelectric system on adult salmonid energetics.

Oregon, Washginton↗

USGS2006

Conceptual model for quantifying pre-smolt production from flow-dependent physical habitat and water temperature

A conceptual model has been developed to test river regulation concepts by linking physical habitat and water temperature with salmonid population and production in cold water streams. Work is in progress to examine numerous questions as part of flow evaluation and habitat restoration programmes in the Trinity River of California and elsewhere. For instance, how much change in pre-smolt chinook salmon ( Oncorhynchus tshawytscha ) production in the Trinity River would result from a different annual instream allocation (i.e. up or down from 271 × 10 6 m 3 released in the late 1980s) and how much change in pre-smolt production would result from a different release pattern (i.e. different from the 8.5 m 3 s −1 year-round release). The conceptual model is being used to: design, integrate and improve young-of-year population data collection efforts; test hypotheses that physical habitat significantly influences movement, growth and mortality of salmonid fishes; and analyse the relative severity of limiting factors during each life stage. The conceptual model, in conjunction with previously developed tools in the Instream Flow Incremental Methodology, should provide the means to more effectively manage a fishery resource below a regulated reservoir and to provide positive feedback to planning of annual reservoir operations.

Regulated Rivers: Research & Management↗

USGS2024

Unique diet and Philonema sp. infections in reservoir-rearing juvenile Chinook Salmon

Objective Dams and reservoirs can alter juvenile growth and survival of migratory salmonids through several physical and biological mechanisms. Juvenile Chinook Salmon Oncorhynchus tshawytscha that are produced upstream of large hydropower dams may have associated passage mortality, but the reservoirs created by these dams can support rapid growth. Characterizing the biotic drivers of growth and mortality in reservoirs may aid in understanding the cumulative effects of river impoundments on migratory salmonid populations. The purpose of this study was to understand how reservoirs facilitate rapid growth in juvenile Chinook Salmon. Methods We analyzed stomach contents to determine diet composition throughout the summer and fall. We also recorded prevalence of the parasitic nematode Philonema sp. in the coeloms of fish. Result We found that juvenile Chinook Salmon frequently consumed young-of-year centrarchids, which likely contributed to rapid growth. Piscivory was highest from July through October and decreased with surface temperature from November through December. Correspondingly, zooplankton and arthropod consumption increased in November and December. Prevalence of visible Philonema sp. infections in the coelom was high (34.6%), negatively associated with time, and nonlinearly associated with fork length. Conclusion These findings reveal unique diet patterns and suggest potential parasite-associated mortality in reservoir-rearing Chinook Salmon, but more detailed studies across a longer time scale are needed to robustly assess the population-level effects of this parasite.

Transaction of the American Fisheries Society↗

USGS1997

Relative sensitivity of three endangered fishes, Colorado squawfish, bonytail, and razorback sucker, to selected metal pollutants

The acute toxicity of four metal pollutants to larval and juvenile stages of endangered Colorado squawfish ( Ptychocheilus lucius ), bonytail ( Gila elegans ), and razorback sucker ( Xyrauchen texanus ) were determined in a water quality representative of that in the Green River, Utah. The rank order of toxicity (96-hr LC 50 ) of the metals to all species and life stages from most toxic to least toxic was mercury (57–168 μg/liter) > cadmium (78–168 μg/liter) > hexavalent chromium (32,000–123,000 μg/liter) > lead (>170,000 μg/liter). In tests with lead, a precipitate formed in all test solutions and no mortalities occurred in these treatments. The larvae of each species were as sensitive or more sensitive than the juveniles to cadmium, hexavalent chromium, and mercury. Overall, the three species exhibited similar sensitivities to cadmium, hexavalent chromium, and mercury. Comparison of test results for the juveniles with toxicity values reported for other freshwater fishes tested in different water qualities indicates that the endangered fishes are more sensitive to cadmium than other cyprinids and centrarchids and less sensitive than salmonids, whereas their sensitivity to hexavalent chromium and mercury is similar to that of other cyprinids, centrarchids, and salmonids.

Ecotoxicology and Environmental Safety↗

USGS2001

Antibody-producting cells correlated with body weight in juvenile Chinook salmon Oncorhynchus tshawytscha acclimated to optimal and elevated temperatures

The immune response of juvenile chinook salmon ( Oncorhynchus tshawytscha ) ranging in weight from approximately 10 to 55 g was compared when the fish were acclimated to either 13 or 21° C. A haemolytic plaque assay was conducted to determine differences in the number of antibody-producing cells (APC) among fish of a similar age but different body weights. Regression analyses revealed significant increases in the number of APC with increasing body weight when fish were acclimated to either water temperature. These results emphasise the importance of standardising fish weight in immunological studies of salmonids before exploring the possible effects of acclimation temperatures.

Fish & Shellfish Immunology↗

USGS1999

Effects of recent volcanic eruptions on aquatic habitat in the Drift River, Alaska, USA: Implications at other Cook Inlet region volcanoes

Numerous drainages supporting productive salmon habitat are surrounded by active volcanoes on the west side of Cook Inlet in south-central Alaska. Eruptions have caused massive quantities of flowing water and sediment to enter the river channels emanating from glaciers and snowfields on these volcanoes. Extensive damage to riparian and aquatic habitat has commonly resulted, and benthic macroinvertebrate and salmonid communities can be affected. Because of the economic importance of Alaska's fisheries, detrimental effects on salmonid habitat can have significant economic implications. The Drift River drains glaciers on the northern and eastern flanks of Redoubt Volcano: During and following eruptions in 1989-1990, severe physical disturbances to the habitat features of the river adversely affected the fishery. Frequent eruptions at other Cook Inlet region volcanoes exemplify the potential effects of volcanic activity on Alaska's important commercial, sport, and subsistence fisheries. Few studies have documented the recovery of aquatic habitat following volcanic eruptions. The eruptions of Redoubt Volcano in 1989-1990 offered an opportunity to examine the recovery of the macroinvertebrate community. Macroinvertebrate community composition and structure in the Drift River were similar in both undisturbed and recently disturbed sites. Additionally, macroinvertebrate samples from sites in nearby undisturbed streams were highly similar to those from some Drift River sites. This similarity and the agreement between the Drift River macroinvertebrate community composition and that predicted by a qualitative model of typical macroinvertebrate communities in glacier-fed rivers indicate that the Drift River macroinvertebrate community is recovering five years after the disturbances associated with the most recent eruptions of Redoubt Volcano.

Environmental Management↗

USGS2004

Intra-strain dioxin sensitivity and morphometric effects in swim-up rainbow trout ( Oncorhynchus mykiss )

Inter and intra-specific differences in sensitivity of early life stage salmonids to 2,3,7,8-TCDD exposure have been reported, but intra-strain differences have not been found in the literature. Our results indicate that intra-strain variability in terms of embryo mortality (LD50) is small in Eagle Lake strain of rainbow trout, LD50 values ranging from 285 to 457 pg TCDD egg g −1 . These results confirm Eagle Lake as a less sensitive strain within rainbow trout, and do not indicate overlap with reported LD50 values for brook or lake trout. Our results also demonstrate that although generalized edema in regions including the yolk-sac are frequently associated with mortality following dioxin exposure, not all edematous fish die. We detected dose-dependent decreases in cranial length, eye diameter, mass, and total length ( P <0.05) in viable swim-up rainbow trout. These effects are presumed to indicate more subtle dose-dependent disruptions of the viteline vein vasculature and, therefore, in access to energy sources. A tendency for dose-dependent decrease in liver glycogen reserves concurred with previous results on salmonids and with the well described TCDD-induced alterations in intermediate metabolism of rats and chicken embryos (wasting syndrome). This syndrome could be contributing to the reduced growth that we observed.

Comparative Biochemistry and Physiology, Part C: T↗

USGS2026

Toxicity of anticoagulant rodenticides on Pacific salmon: Assessing lethal and sublethal effects

To restore native biodiversity on island ecosystems containing invasive rodents, partial- and whole-island eradications generally rely on broadcast baiting with anticoagulant rodenticides (ARs). This approach can result in bait pellets entering aquatic environments, raising concerns about effects to non-target fish. Salmonids are a dominant group of fishes on many temperate islands targeted for rodent eradication, and AR toxicity data for salmonids are limited. Our goal was to determine if coho salmon ( Oncorhynchus kisutch ) are susceptible to coagulopathy and death via exposure to commonly used ARs. We assessed risk of ARs to coho using dose-response curves generated through intraperitoneal injections after determining that coho would not directly ingest the AR baits. Median lethal doses (96-h LD 50 ) estimated using 100 % corn oil carrier were 85.7 µg/g for brodifacoum and 54.0 µg/g for diphacinone. Acetone (30–41 %), used to dissolve ARs in corn oil, reduced the toxicity of diphacinone (LD 50 = 102.3 µg/g, p < 0.001) but not brodifacoum (LD 50 = 73.3 µg/g, p = 0.126) indicating that solvent choice can influence toxicity outcomes. Behavioral changes and onset of mortality differed between the two ARs, with diphacinone acting more rapidly. Tissue analysis supported a difference in toxicokinetics between the two ARs, with significant decreases in liver and muscle residues for diphacinone but not brodifacoum. Sublethal brodifacoum exposure (53.9 µg/g; LD 13 ) impaired blood clotting at 72- and 96- h but returned to baseline by 120 h. No clotting impairment was observed up to 144 h after diphacinone exposure (45.5 µg/g; LD 4 ), suggesting a non-coagulopathy mode of action. These findings will inform risk assessments when considering use of these ARs for rodent management near streams and shorelines and clearly demonstrate that brodifacoum causes coagulopathy in coho.

Ecotoxciology and Environmental Safety↗

USGS2023

Characterization of maternal immunity following vaccination of broodstock against IHNV or Flavobacterium psychrophilum in rainbow trout (Oncorhynchus mykiss)

Infectious hematopoietic necrosis (IHN) is a significant viral disease affecting salmonids, whereas Flavobacterium psychrophilum (Fp), the causative agent of bacterial coldwater disease (BCWD), remains one of the most significant bacterial pathogens of salmonids. We explored maternal immunity in the context of IHN and BCWD management in rainbow trout ( Oncorhynchus mykiss ) aquaculture. Two experimental trials were conducted where different groups of female broodstock were immunized prior to spawning with an IHNV DNA vaccine or a live attenuated F. psychrophilum (Fp B.17-ILM) vaccine alone, or in combination. Progeny were challenged with either a low or high dose of IHNV at 13 days post hatch (dph) and 32 dph or challenged with F. psychrophilum at 13 dph. Mortality following a low-dose IHNV challenge at 13 dph was significantly lower in progeny from vaccinated broodstock vs. unvaccinated broodstock, but no significant differences were observed at 32 dph. Mortality due to BCWD was also significantly reduced in 13 dph fry that originated from broodstock immunized with the Fp B.17-ILM vaccine. After vaccination broodstock developed specific or neutralizing antibodies respectively to F. psychrophilum and IHNV; however, antibody titers in eggs and fry were undetectable. In the eggs and fry mRNA transcripts of the complement components C3 and C5 were detected at much higher levels in progeny from vaccinated broodstock and showed a significantly increased and rapid response post-challenge compared with unvaccinated broodstock. After challenges pro-inflammatory cytokine expression was immediately and considerably elevated in the fry from vaccinated broodstock vs. unvaccinated broodstock, whereas adaptive immune genes were elevated to a lesser degree. Results suggest that maternal transfer of innate and adaptive factors at the transcript level occurred because development of lymphomyeloid organs is not complete in such young fry. In addition to documenting maternally derived immunity in teleosts, this study demonstrates that broodstock vaccination can confer some degree of protection to progeny against viral and bacterial pathogens.

Fish and Shellfish Immunology↗