Spatial and temporal patterns in fertilization and settlement of young gag (Mycteroperca microlepis) along the West Florida Shelf

We used otolith analyses of juvenile gag, Mycteroperca microlepis (Goode and Bean, 1879) settling in seagrass beds along the west Florida coast over a 4-yr period (1994 through 1997) to examine regional and temporal differences in fertilization date, pelagic larval duration, and settlement date. We found annually consistent geographic patterns in the mean fertilization and settlement dates of juvenile gag. These dates were several weeks earlier for fish recruiting south of 28° N than they were for fish recruiting north of 28° N. While it was beyond the scope of this study to determine the processes responsible for these patterns, we consider several possible mechanisms that might account for the patterns we observed. These include (1) a north-south difference in spawning times, (2) a year-to-year change in wind-driven surface currents affecting distribution during the pelagic larval phase, and (3) a north-south difference in seagrass habitat available to settlers. The patterns did not appear to result from differences in spawning time, seasonal changes in wind driven surface currents, or seagrass habitat availability. However, both pelagic larval duration and the time differences between west Florida gag populations and those from Campeche Bank are consistent with the appearance of earlier-spawned juveniles in south Florida. Transport from Campeche Bank is possible via the Loop Current. Our modeling of onshore movement considered only the wind forcing of the surface layer, essentially a two-dimensional model. A three-dimensional model would be useful to evaluate transport at various depths.