Prey availability, environmental constraints, and aggregation dictate population distribution of an imperiled fish

The study took a spatiotemporal modeling approach in an effort to account for sampling and observation variation by employing both stochastic and deterministic elements. Smelt density was spatially and temporally autocorrelated, strongly tracking prey availability, while constrained by hydrological factors, salinity, turbidity, and velocity. Specifically, juvenile smelt preferred slightly saline, turbid, and slow‐moving water with ample copepod prey. Poor swimming capabilities reduced the capacity of juvenile delts smelt to mix throughout the estuary and disperse from areas with habitat of lesser quality to locate areas that offer better habitat conditions. Through-Delta outflow appeared to influence the spatial distribution of covariates and juvenile smelt, with delta smelt densities tending to peak closer to the marine zone at a lower maximal value when outflow was higher. Predictions from the model matched observed patterns of juvenile delta smelt occurrence while embracing uncertainty, although the predictions tended to overestimate total smelt catch variation via over‐predicted tail values. The results indicate that data‐driven improvements can be made to the analytical methods currently used to guide delta smelt management and address the impacts on delta smelt and its habitat from environmental stressors, habitat alteration, and climate change.

 

Simonis JL and JE Merz. 2019. Prey availability, environmental constraints, and aggregation dictate population distribution of an imperiled fish. Ecosphere 10:e02634

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