Relative Importance of Fishing and Natural Mortality of Spotted Seatrout at Northern Latitudinal Limits

Spotted seatrout, Cynoscion nebulosus, is one of the most economically important sportfish in North Carolina.  The state’s recent stock assessment concluded the population is overfished; however, the extent to which variability in natural mortality (M) affects annual estimates of fishing mortality (F) is unknown.  This is potentially important because North Carolina is near the species’ northern latitudinal limit, where spotted seatrout are particularly vulnerable to lethal winter conditions.  Data from the first comprehensive tag-return study of spotted seatrout in North Carolina, along with fishery-independent gill net survey data collected by the state, were used to estimate F and M.  From September 2008 through October 2012, our estimates indicate that M exceeded F and winter severity strongly influenced M.  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 fixed using general life-history relationships based on weight and longevity.  Effective management of this valuable fishery relies on an accurate understanding of the relative importance of harvest and winterkill on population dynamics.  Future assessments of spotted seatrout in North Carolina would be improved by consideration of more direct estimates of and annual variability in M.