Larval assemblages of large and medium-sized pelagic species in the Straits of Florida

Critical gaps in our understanding of the distributions, interactions, life histories and preferred habitats of large and medium-size pelagic fishes severely constrain the implementation of ecosystem-based, spatially structured fisheries management approaches. In particular, spawning distributions and the environmental characteristics associated with the early life stages are poorly documented. In this study, we consider the diversity, assemblages, and associated habitat of the larvae of large and medium-sized pelagic species collected during 2 years of monthly surveys across the Straits of Florida. In total, 36 taxa and 14,295 individuals were collected, with the highest diversity occurring during the summer and in the western, frontal region of the Florida Current. Only a few species (e.g. Thunnus obesus, T. alalunga, Tetrapturus pfluegeri) considered for this study were absent. Small scombrids (e.g. T. atlanticus, Katsuwonus pelamis, Auxis spp.) and gempylids dominated the catch and were orders of magnitude more abundant than many of the rare species (e.g. Thunnus thynnus, Kajikia albida). Both constrained (CCA) and unconstrained (NMDS) multivariate analyses revealed a number of species groupings including: (1) a summer Florida edge assemblage (e.g. Auxis spp., Euthynnus alleterattus, Istiophorus platypterus); (2) a summer offshore assemblage (e.g. Makaira nigricans, T. atlanticus, Ruvettus pretiosus, Lampris guttatus); (3) an ubiquitous assemblage (e.g. K. pelamis, Coryphaena hippurus, Xiphias gladius); and (4) a spring/winter assemblage that was widely dispersed in space (e.g. trachipterids). The primary environmental factors associated with these assemblages were sea-surface temperature (highest in summer-early fall), day length (highest in early summer), thermocline depth (shallowest on the Florida side) and fluorescence (highest on the Florida side). Overall, the results of this study provide insights into how a remarkable diversity of pelagic species spatially and temporally partition spawning within a region that is characterized by dynamic oceanography and strong habitat gradients.