Objective The objectives of this study were to develop joint tag-recovery models that make use of both live- and dead-tag-recovery data to estimate fishing and natural mortality and allow for an evaluation of hypotheses at the individual fish scale. Such models are useful for fisheries that have relatively high rates of catch-and-release fishing in addition to harvest.Methods State-space models were developed that make use of tag-return data from fish that were harvested and/or released in a joint-likelihood model using Bayesian methods. The accuracy of the models was assessed using simulation techniques. Additionally, the models were fit to data from four fisheries in Idaho, including Smallmouth Bass Micropterus dolomieu in Dworshak Reservoir and Lake Pend Oreille, Yellow Perch Perca flavescens in Cascade Reservoir, and Lake Trout Salvelinus namaycush in Priest Lake. In addition to the null model, which contained time- and individual-invariant parameters, a time-varying model and a model that allowed fishing and natural mortality to vary based on length at tagging were also fit.Results The simulation results suggested that the state-space models were relatively unbiased and the models that used both live- and dead-tag recoveries were more accurate than those that used only harvest data. Estimated natural mortality was greater than fishing mortality at all four fisheries in the study. The direction and magnitude of the effect of length on fishing and natural mortality varied among the fisheries. The model that included length was the top model for Smallmouth Bass in Dworshak Reservoir, Yellow Perch in Cascade Reservoir, and Lake Trout in Priest Lake, whereas the time model was the top model for Smallmouth Bass in Lake Pend Oreille.Conclusions The state-space models described in this study provide a framework for estimating the demographic parameters that is more flexible than those of the previously published instantaneous rate models. The models are easily extensible to evaluate numerous hypotheses or accommodate additional data that can greatly benefit management or conservation of fisheries with concurrent harvest and catch-and-release components. In this study state-space joint tag-recovery models that make use of both live- and dead-tag-recovery data were developed to estimate fishing and natural mortality and allow for the evaluation of hypotheses at the individual fish scale.
Objective Jaguar Guapote Parachromis managuensis and Red Devil/Midas cichlids Amphilophus spp. are highly invasive species in the family Cichlidae native to Central America. These cichlids are popular within the aquarium trade, leading to their broad introduction outside of their native range. Information about potential environmental plasticity of a species can improve predictions of invasion potential. In this respect, measures of environmental influences on metabolic rate and hypoxia tolerance are important for understanding limitations in adaptability and subsequently guiding the management of invasive species.Methods Standard metabolic rate (SMR), hypoxia tolerance, and critical thermal maxima (CTmax) were compared between Jaguar Guapote and Amphilophus spp. For SMR and hypoxia tolerance, a range of temperatures spanning subtropical to tropical environments (i.e., 22, 28, and 34 degrees C) was used, followed by stepwise decreases in oxygen saturation until loss of equilibrium.Results Jaguar Guapote and Amphilophus spp. both had lower SMR at 28 degrees C than at 34 degrees C, SMR at 22 degrees C was not different from either temperature. Both Jaguar Guapote and Amphilophus spp. were the most sensitive to hypoxia at the coolest temperature (22 degrees C) relative to warmer temperatures (28 degrees C and 34 degrees C). Upper thermal tolerance (CTmax) was similar between species (similar to 42 degrees C), although Jaguar Guapote were more resilient based on a higher agitation temperature and recovery following high temperature exposure.Conclusions These results indicate temperatures that are representative of their natural distribution (i.e., near 28 degrees C) offer energetic savings for Jaguar Guapote and Amphilophus spp. relative to warmer temperatures (34 degrees C), with cooler temperatures (22 degrees C) having higher metabolic costs than expected. Both Jaguar Guapote and Amphilophus spp. are sensitive to hypoxia at cooler temperatures (22 degrees C). Therefore, these species are relatively resilient to high temperatures, but low temperatures may restrict their invasiveness. Temperature effects on metabolic rate, lower oxygen tolerance, and upper thermal tolerance were evaluated for two tropical invasive fish species. These species were more resilient to warmer than cooler temperatures than would be expected in their natural habitats. Lower temperatures are likely to limit their invasive potential.
Objective Reproduction and recruitment represent distinct demographic processes that may independently limit establishment and spread of an invasive species. We evaluated reproduction and recruitment success of Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix in the Ohio River basin across multiple spatial and temporal scales to identify potential demographic bottlenecks.Methods We assessed detection/nondetection data on Bighead Carp and Silver Carp eggs/larvae and young of the year (age 0) to provide information on these species' reproduction and recruitment, respectively. Data were assessed at reach-level (i.e., pool) and site-level spatial scales and at annual and intra-annual temporal scales throughout the Ohio River basin, relating patterns of egg/larval and young-of-the-year occurrence to adult relative abundance, hydrologic conditions, and nursery habitat availability.Results Estimated occurrence of Bighead Carp eggs/larvae and young of the year was inconsistent throughout the study area, suggesting limited establishment success in the Ohio River. Silver Carp egg/larval persistence probability was primarily associated with adult densities rather than variation in flow or temperature, and eggs were estimated to occur across a large portion of the basin. However, Silver Carp young-of-the-year occurrence appeared to be spatially restricted. Annual pool and intra-annual site young-of-the-year persistence probability was correlated with the availability of nursery habitat at both scales. Young of the year were consistently detected at only one location, a floodplain lake (Hovey Lake) in the John T. Myers pool, indicating the presence of a potential localized source population in this location.Conclusions Silver Carp eggs/larvae were detected across much of the invaded portion of the Ohio River, suggesting that reproduction is widespread. However, young-of-the-year occurrence was most strongly associated with nursery habitat. In the Ohio River, the lack of widespread nursery habitat may be limiting the recruitment success of young-of-the-year Silver Carp into the population, potentially creating a demographic bottleneck that constrains their spread in this basin. Bighead Carp and Silver Carp are spreading in U.S. rivers, but in the Ohio River their expansion may be slowed due to lower availability of suitable nursery habitat. Identifying and managing these key habitats could help to limit future impacts.
Objective Understanding how environmental variables influence the timing of spawning is important for the conservation of imperiled fishes like the endangered Atlantic Sturgeon Acipenser oxyrinchus. We observed mature Atlantic Sturgeon volitionally spawning in captivity over a 14-year period to evaluate the change in how both spawn timing and the daily probability of spawning changed in response to environmental (temperature, photoperiod, lunar cycle) and biological (individual females) variables. Methods Adults were held at Bears Bluff National Fish Hatchery in seminatural conditions mimicking the Altamaha River temperature profile and under natural photoperiod. We fit Bayesian linear regression models using a suite of covariates to represent patterns in environmental conditions across several time periods in advance of when spawning was observed. Results A total of 35 volitional spawning events were observed over the study period, with 31 assigned to individual females. The average interval between spawning events for individual females was 1.7 years (range = 1-9 years). Atlantic Sturgeon responded more to cumulative thermal conditions in the lead-up to spawning compared with fluctuations in temperature closer to the observed event, with mean water temperature the 30 d prior to spawning and accumulated thermal units over the same period being the strongest predictors of spawning time. Median spawning time was August 21 at an average temperature of 22.7 degrees C (range = 20.9-25.3 degrees C), and with each 1 degrees C increase in the mean temperature over the preceding 30 d, spawning advanced by 16.7 d. The cumulative probability that spawning would occur increased sharply as photoperiod declined past 14 h and reached its maximum near a day length of 13.2 h. Conclusions Volitional spawning produced viable offspring, and the approach could be considered for conservation efforts. Individual females spawned volitionally in captivity in consecutive years, which is not well documented for any sturgeon species. Results add to our understanding of the reproductive ecology of the species that can supplement results from monitoring in the wild. For fall-spawning Atlantic Sturgeon, our results help to shed light on uncertainties related to long-term implications of climate change on thermal conditions for spawning and early life stage rearing.
Objective Although rotenone has been used to remove nonnative fish populations in the United States since 1934, the factors influencing its persistence remain unclear, even though under- and overapplication have substantial social, financial, and ecological consequences. Here, we quantified the variation in rotenone persistence across streams and evaluated the environmental drivers associated with rotenone loss during treatments.Methods We measured physical and chemical stream characteristics that are hypothesized to impact rotenone persistence across 21 montane streams and collected rotenone mass flux measurements every hour for a 7-h treatment. We then fitted generalized linear models to quantify the influence of stream characteristics on rotenone persistence.Results Physical, chemical, and stream bed characteristics varied widely across the 21 sample reaches. Patterns in rotenone mass flux at our lowest measurement location showed high variability compared with upstream measurements. Vegetation, conductivity, and gradient were the strongest predictors in the generalized linear models and were all negatively associated with rotenone persistence.Conclusion The variability in rotenone persistence and the relatively strong influence of factors that influence rotenone persistence emphasize the need for practitioners to carefully consider rotenone treatments in streams. We suggest a framework and working model to help guide pretreatment surveys and bioassays that can greatly increase the potential for successful rotenone treatments. Rotenone concentrations during treatments are influenced by physical and chemical stream conditions, resulting in variable rotenone persistence. We suggest a framework for increasing efficacy of rotenone treatments in future applications.
