A NUMERICAL STUDY OF LARVAL FISH RETENTION ALONG THE SOUTHEAST FLORIDA COAST

The possibility that the eggs and larvae of southeast Florida fishes c an be retained by local hydrodynamic processes is examined using simpl e idealizations of the local currents, oceanic turbulence, Ekman drift , horizontal larval swimming and larval mortality. The simulated settl ing rates were greatly affected by the interaction between the hydrody namics and the degree of spatial heterogeneity in the mortality fields . In the presence of an onshore Ekman drift, for example, settling rat es tended to increase unless the mortality rate over the reef was much higher than elsewhere. Overall, the simulations suggest that the mean ders, eddies and gyres associated with the Florida current front can r etain between 0.07 and 41% of the larvae with planktonic life spans on the order of 1 month. However, only a recirculating gyre enabled larg e numbers of larvae to settle within a few kilometers of their birth p lace. Assuming the mortality rate near the reef is 20-90% per day, but lower offshore, between 0.1 and 7% of the larvae retained are likely to settle. This implies that southeast Florida reef fish populations s hould be able to replenish themselves without relying on upstream sour ces of recruitment, provided they exhibit normal fecundities. The simu lations also suggest that natural levels of variation in the mortality held or local currents can both cause large fluctuations in recruitme nt. (C) 1998 Elsevier Science B.V. All rights reserved.