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This Article is brought to you for free and open access by the Natural Resources, School of at DigitalCommons@University of Nebraska -Lincoln. It has been accepted for inclusion in Papers in Natural Resources by an authorized administrator of DigitalCommons@University of Nebraska -Lincoln.Breeggemann, Jason J.; Kaemingk, Mark A.; DeBates, Timothy J.; Paukert, Craig P.; Krause, Jacob R.; Letvin, Alexander P.; Stevens, Tanner M.; Willis, David W.; and Chipps, Steven R., "Potential Direct and Indirect Effects of Climate Change on a Shallow Natural Lake Fish Assemblage" (2016 ). Bioenergetics models were used to simulate the effects of climate change on growth and food consumption using predicted 2040 and 2060 temperatures in a shallow Nebraska Sandhill lake, USA. The patterns and magnitude of daily and cumulative consumption during the growing season (April-October) were generally similar between the two predators. However, growth of northern pike was always reduced (À3 to À45% change) compared to largemouth bass that experienced subtle changes (4 to À6% change) in weight by the end of the growing season. Assuming similar population size structure and numbers of predators in 2040-2060, future consumption of bluegill and yellow perch by northern pike and largemouth bass will likely increase (range: 3-24%), necessitating greater prey biomass to meet future energy demands. The timing of increased predator consumption will likely shift towards spring and fall (compared to summer), when prey species may not be available in the quantities required. Our findings suggest that increased water temperatures may affect species at the edge of their native range (i.e. northern pike) and a potential mismatch between predator and prey could exist.

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The addition of acoustic telemetry to conventional tagging studies can generate direct estimates of mortality and movement rates to inform fisheries management. We applied a combined telemetry and tag-return design to southern flounder (Paralichthys lethostigma), a coastal flatfish that demonstrates limited movements within estuarine habitats coupled with extensive ontogenetic migrations that present unique challenges for estimating mortality rates. The fates of acoustically and conventionally tagged fish were followed during 2014–2016 to estimate annual rates of fishing mortality (F), natural mortality (M), and estuarine emigration (E). Multistate models estimated southern flounder annual F for each of the 3 years at two spatial scales (New River estuary F = 0.49–1.61; North Carolina coast F = 0.36–0.72). Annual rates of emigration were high (E = 1.06–1.67), and direct estimation of this source of loss considerably improved mortality estimates. The model estimated natural mortality as a constant annual rate (M = 0.84), which was similar in magnitude to life-history-based estimates for similar age groups. By accounting for unique behavioral attributes in the study design, the application of multistate tagging models provided robust estimates of mortality and emigration rates for a valuable coastal fishery resource that will inform future efforts to achieve yield and conservation goals.

The need to characterize and track coastal hypoxia has led to the development of geostatistical models based on in situ observations of dissolved oxygen (DO) and mechanistic models based on a representation of biophysical processes. To integrate the benefits of these two distinct modeling approaches, we develop a space−time geostatistical framework for synthesizing DO observations with hydrodynamic−biogeochemical model simulations and meteorological time series (as covariates). This fusion-based approach is used to estimate hypoxia in the northern Gulf of Mexico across summers from 1985 to 2017. Deterministic trends with dynamic covariates explain over 35% of the variability in DO. Moreover, cross-validation results indicate that 58% of DO variability is explained when combining these trends with spatiotemporal interpolation, which is substantially better than mechanistic or conventional geostatistical hypoxia modeling alone. The fusion-based approach also reduces hypoxic area uncertainties by 11% on average and up to 40% in months with sparse sampling. Moreover, our new estimates of mean summer hypoxic area changed by >10% in a majority of years, relative to previous geostatistical estimates. These fusion-based estimates can be a valuable resource when assessing the influence of hypoxia on the coastal ecosystem.

The Weakfish Cynoscion regalis, an economically important species, has declined over the last 30 years, corresponding with an increase in total mortality according to the most recent stock assessment. We estimated estuarinespecific and coastwide apparent survival of Weakfish by using a Cormack-Jolly-Seber model to provide insights into the spatiotemporal component of mortality. Telemetered Weakfish (n = 342) were released across five estuaries ranging from North Carolina to New Jersey between 2006 and 2016. In estuaries from Delaware Bay and northward, egress peaked around the third week of September; in North Carolina, egress peaked by the first week of November. For three estuaries with adequate sample sizes, apparent survival estimates were similar and a joint model including all telemetered Weakfish estimated an extremely low annual apparent survival rate of 0.001 (95% credible interval [CrI] = 0.002-0.0003) or annual apparent instantaneous total mortality of 7.25 (95% CrI = 6.28-8.05). At a minimum, 61% of telemetered Weakfish emigrated in the fall, but only 2 of 149 fish with long-lived transmitters were detected as returning to estuaries the following year. This is a small proportion for a fish that exhibits spawning site fidelity. We conclude that the disappearance of telemetered Weakfish represents mortality that occurs between emigration and the spring spawning period, potentially during overwinter periods on the continental shelf. Our study provides insights into the magnitude, timing, and location of Weakfish loss and facilitates an improved understanding of Weakfish population dynamics for use in stock rebuilding.

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