Estimating Fishing and Natural Mortality of Spotted Seatrout in North Carolina Using Conventional and Telemetry Tagging

Spotted seatrout (Cynoscion nebulosus) are the most targeted marine recreational species in North Carolina.  The state’s recent assessment concluded the population is overfished; however, the extent to which variability in natural mortality (M), particularly during winter, affects annual estimates of fishing mortality (F) is unknown.  This is potentially important for spotted seatrout in North Carolina because they are near the northern extent of their geographic range.  We are using data from the first comprehensive tag return and telemetry study of spotted seatrout in North Carolina to directly estimate F, M, and movement.  We conducted both laboratory and field studies to obtain estimates of auxiliary parameters (e.g., reporting rate, tag retention, and tagging-induced mortality) necessary for our tag return modeling.  There was no mortality associated with conventional or telemetry tagging but reporting rate and tag loss of conventional tags significantly limited returns in our study.  From 2008 to 2011, our tag return experiment generated bimonthly estimates of F ranging from 0.004 to 0.045, and M ranging from zero to 1.750.  Both movement and M of telemetered spotted seatrout were strongly influenced by water temperature; M increased abruptly at temperatures below approximately 6°C.  Direct telemetry-based estimates of monthly M during winter in a single region of the state were high and similar to those estimated indirectly by our tag return experiment that was conducted throughout the state.  Our annual estimates of F were lower and M higher than those reported for spotted seatrout in North Carolina’s recent age-based stock assessment, where M was both fixed and indirectly estimated through life-history parameters. Future assessments of spotted seatrout in North Carolina would be improved by consideration of more direct estimates of and annual variability in M.