Abundance, Distribution, and Mortality of Young-of-the-Year Spotted Seatrout Cynoscion nebulosus in Three Estuaries Along the Gulf Coast of Florida

Gary A. Nelson and Deborah Leffler, Florida Department of Environmental Protection, Florida Marine Research Institute, 100 Eighth Avenue SE, St. Petersburg, Florida 33701; Voice 727-896-8626 x 2106 E-Mail nelson_ga@epic7.dep.state.fl.us

Data gathered during fixed station and random sampling conducted from 1989-1997 were used to examine spatial and temporal patterns in the abundance and size structure of young-of-the-year (YOY) spotted seatrout, Cynoscion nebulosus, in three Florida estuaries. Young-of-the-year seatrout first appeared at shallow-water (<1.5 m) seine sites during May-June in Choctawhatchee Bay (Florida Panhandle) and in April-May in Tampa Bay and Charlotte Harbor (both along the southwest Florida peninsula). They were first caught at deep-water (<2.3 m) trawl stations about one to three months after their initial appearance at the shallow-water seine sites. Abundance peaked generally during June-July, declined during July-August, and peaked again during September-October in all bays. Changes in size structure concurrent with changes in abundance suggested that seatrout respond to the high temperatures (>30^oC) of mid-summer by moving from shallow-water areas. In Tampa Bay, the probability of capturing YOY seatrout in seines was highest at deep-water, low-salinity sites with bottom vegetation, mud sediments, mangrove stands, and high levels of dissolved oxygen. In Charlotte Harbor, it was highest at deep, low-salinity sites with bottom vegetation. In Choctawhatchee Bay, the probability of capturing YOY seatrout was highest at seine sites with bottom vegetation and mud sediments. Instantaneous total mortality rates, estimated by using an age-length key for the Tampa Bay population, ranged from 0.025 to 0.027/day.