Quantifying intra-annual changes in abundance and distribution to identify the magnitude and scale of potential mortality events

Characterizing the abundance of fish over both space and time can be important to fisheries management. Spotted seatrout (Cynoscion nebulosus) are a warm-temperate estuarine-dependent species prevalent throughout the U.S. South Atlantic and Gulf of Mexico. In North Carolina and Virginia, they are at the species’ northern distributional extent and are therefore more susceptible to low temperature extremes in winter. In this study, we used a Vector Autoregressive Spatiotemporal model (VAST) to quantify the seasonal variation in the abundance and distribution of spotted seatrout within North Carolina waters and examine its relationship with the severity of cold stun events. We found that seasonal declines in relative abundance between the fall/winter and the following spring/summer periods is significantly correlated with low temperature events (i.e., numbers of days of water temperature below $7°C$), indicating cold stun events, depending on its scale and severity, have negative impacts on spotted seatrout population. Lastly, changes in the seasonal spatial density of spotted seatrout elucidated the spatial extent and scale of cold stun events. Together, these results corroborate previous findings that winter temperatures below $7°C$ increase natural mortality to the extent that lower abundance is observed at the population level.