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Sturgeons are among the most endangered fishes in the world. Identifying habitat use characteristics to inform restoration projects is crucial for recovery. However, small sample sizes, inadequate replication of studies, and limited spatial extents complicate our ability to effectively apply the findings of single studies to endangered species conservation across the larger riverscape. We synthesized information from amphidromous and anadromous sturgeons in North America to identify species-specific knowledge gaps and conduct a quantitative comparison of species–habitat relationships. We provided a qualitative summary of substrate use and synthesized estimates of depth and velocity during spawning and non-spawning activity. Generalized patterns among species were identified, such as spawning in fast water on hard substrate and then using slow water with soft substrate areas when not spawning. We noted species-specific variability during spawning that may be attributed to historical maximum length, egg characteristics, and watershed features. This study provides some of the first estimates of habitat use that can be adapted for many populations. Results can contribute to empirically grounded decision-support tools used to prioritize information needs for recovery. [ABSTRACT FROM AUTHOR]

Structured decision making allows reintroduction decisions to be made despite uncertainty by linking reintroduction goals with alternative management actions through predictive models of ecological processes. We developed a decision model to evaluate the trade-offs between six bull trout ( Salvelinus confluentus) reintroduction decisions with the goal of maximizing the number of adults in the recipient population without reducing the donor population to an unacceptable level. Sensitivity analyses suggested that the decision identity and outcome were most influenced by survival parameters that result in increased adult abundance in the recipient population, increased juvenile survival in the donor and recipient populations, adult fecundity rates, and sex ratio. The decision was least sensitive to survival parameters associated with the captive-reared population, the effect of naivety on released individuals, and juvenile carrying capacity of the reintroduced population. The model and sensitivity analyses can serve as the foundation for formal adaptive management and improved effectiveness, efficiency, and transparency of bull trout reintroduction decisions. [ABSTRACT FROM AUTHOR]

The development of effective nonlethal biomonitoring techniques is imperative for the preservation of imperiled freshwater mussel populations. Changes in hemolymph chemistry profiles and tissue glycogen are potential biomarkers for nonlethally monitoring stress in mussels. We sampled three species in the Flint River Basin over 2 years to evaluate how these hemolymph and tissue biomarkers responded to environmental changes. We used hierarchical linear models to evaluate the relationships between variation in the biomarkers and environmental factors and found that the responses of the hemolymph and tissue parameters were strongly related to stream discharge. Shifts in alanine aminotransferase and glycogen showed the largest relations with discharge at the time of sampling, while magnesium levels were most explained by the discharge for 5 days prior to sampling. Aspartate aminotransferase, bicarbonate, and calcium showed the strongest relations with mean discharge for 15 days prior to sampling. The modeling results indicated that biomarker responses varied substantially among individuals of different size, sex, and species and illustrated the value of hierarchical modeling techniques to account for the inherent complexity of aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Freshwater mussel populations are highly susceptible to environmental alterations because of their diminished numbers and primarily sessile behaviors; nonlethal biomonitoring programs are needed to evaluate the health of populations prior to mass mortality events. Our objectives were to determine ( i) which biochemical parameters in freshwater mussel hemolymph could be consistently quantified, ( ii) how hemolymph parameters and tissue glycogen respond to a thermal stress gradient (25, 30, and 35 °C), and ( iii) the effects of tissue and hemolymph extraction on long-term growth and survival of smaller- and larger-bodied mussel species. Glucose exhibited elevated expression in both species with increasing water temperature. Two transaminase enzymes had elevated expression in the 30 °C treatment. The effects of hemolymph extraction and tissue biopsies were evaluated with a large-bodied species, Elliptio crassidens, and a smaller species, Villosa vibex. Individuals were monitored for 820 to 945 days after one of four treatments: hemolymph extraction, tissue biopsy, tissue and hemolymph extraction, and control. Hemolymph extraction and tissue biopsy adversely affected survival of V. vibex, suggesting that these extraction methods may add some risk of reduced survival to smaller-bodied species. Survival of E. crassidens was not impaired by any of the treatments, supporting the use of these techniques in nonlethal biomonitoring programs for larger-bodied mussel species. [ABSTRACT FROM AUTHOR]

We evaluated competing models explaining the occurrence of five stream fishes in an urbanizing watershed to determine the relative importance of (a) impervious surface and other indicators of current land use, (b) historic land use (e.g., agriculture, impoundments), and (c) hydrogeomorphic characteristics (e.g., stream size, elevation, geology). For four of five species, the best-supported models were those that included both current effective impervious cover and historic land use predictor variables, although models with only effective impervious cover were equally well supported for two of those species. For the best-supported models for three species, occurrence probability was predicted to approach zero at levels of development equivalent to about 2%–4% effective impervious cover in the surrounding region. Data were drawn from 357 fish collections made in the Etowah River basin, Georgia, USA, between 1998 and 2003 and analyzed using hierarchical logistic regression accounting for imperfect species detection. This is the first study we know of to examine the response of individual fish species to both increasing impervious cover and historic land use. Such individual species assessments will be increasingly necessary to guide policies for managing urban effects and preventing extirpations of sensitive species. [ABSTRACT FROM AUTHOR]

Invasions of non-native brook trout (Salvelinus fontinalis) have the potential for upstream displacement or elimination of bull trout (Salvelinus confluentus) and other native species already threatened by habitat loss. We summarized the distribution and number of bull trout in samples from 12 streams with and without brook trout in central Idaho and used hierarchical regression analysis to consider whether brook trout have displaced bull trout along gradients of temperature and elevation. Brook trout generally were observed in higher numbers downstream of bull trout. Brook trout presence, number, and both temperature and elevation were important variables explaining the observed distributions and number of bull trout among streams. Our analyses support the hypothesis that brook trout have displaced bull trout, but results were highly variable and stream dependent. Although brook trout appeared to have displaced bull trout to higher elevations or colder temperatures, there was no clear influence on overall number of bull trout. Brook trout probably do influence bull trout populations and facilitate if not cause local extinctions, but threats probably vary strongly with environmental conditions. Bull trout in smaller streams could be more vulnerable than those in larger streams. [ABSTRACT FROM AUTHOR]

Management of mixed-stock Chinook salmon (Oncorhynchus tshawytscha) fisheries requires balancing fishery access and conservation of vulnerable stocks. Although accurate, timely estimates of stock-specific harvest are crucial in achieving competing objectives, limited numbers of stock assignments (e.g., tag recoveries) can diminish the utility of estimates. We used a flexible simulation approach, applied to both a theoretical and real-world fishery case study, to compare the performance of competing monitoring alternatives and estimators for harvest. We sought to improve accuracy for point estimates of harvest and harvest trajectories over time. Bayesian models provided similarly accurate point estimates to existing models at high levels of data aggregation, generally improved estimates of harvest trajectories at intermediate aggregation, and reliable estimates of uncertainty. Incorporation of time-lagged prior information inconsistently improved estimates of harvest trajectories. Among monitoring alternatives yielding equal increases (33%) in coded wire tag recoveries, increasing tagging rates resulted in the greatest decrease in estimate uncertainty for target stocks (37.5% to 45.3%). Variable performances of mixed-stock harvest estimators suggest their use should considered on a stock- and fishery-specific basis, potentially using a simulation-based approach. [ABSTRACT FROM AUTHOR]