Spatial and Temporal Heterogeneity of Fish Spawning Dynamics on the West Florida Shelf During Fall

Identifying spawning areas for economically and ecologically important fishes is critical for fisheries conservation and ecosystem-based management. We used genetic barcoding to identify fish eggs collected across the West Florida Shelf (WFS) during September of 2013, 2014, and 2019. Fish eggs were collected on Southeast Area Monitoring and Assessment Program (SEAMAP) ichthyoplankton cruises using a Continuous Underway Fish Egg Sampler. Analysis of 4833 fish eggs from the 3 years resulted in the identification of 82 species within 35 families. A 78% DNA barcoding success rate was achieved, with 46% of all identifications being at the species level. PERMANOVA results revealed significant differences in fish egg beta-diversity across time (the 3 years sampled) and space (preassigned levels of both depth class and regional strata). Our findings generally aligned with known adult fish distributions and spawning patterns, and we found that water-column depth played a more important role than regional strata in structuring the fish egg assemblages. Eggs from several economically important species were collected and observed at relatively high frequencies, including red snapper, lane snapper, vermilion snapper, yellowedge grouper, and king mackerel. We used the West Florida Coastal Ocean Model to hindcast the trajectories of all fish eggs and trace them back to possible spawning locations. We conducted backward tracking over a span of 36 h based on the assumption that most fish eggs on the WFS undergo hatching within this time window. The model estimated egg transport distances ranging from 1 to 79 km (mean distance of ~21 km), with greater transport distances estimated on the outer shelf in comparison to the middle and inner shelf. These results further our understanding of the spatial and interannual variation of fish spawning dynamics on the WFS and mark the beginning of a long-term monitoring effort.