Faunal Composition and Spatiotemporal Dynamics of Tuna (Family: Scombridae; Tribe: Thunnini) Early Life Stages in the Oceanic Gulf of Mexico

Guy Harvey Oceanographic Center Facility

Fishes of the family Scombridae (tunas, mackerels and bonitos) are of high economic and ecological value worldwide, as they are heavily targeted by commercial and recreational fisheries. In coastal and open-ocean environments, adult tunas are high-level predators, while larval and juvenile tunas serve as prey for numerous species. Much is known about the distribution and abundance of adult tunas, but high taxonomic uncertainty and limited knowledge regarding the distributional patterns of larval and juvenile tunas have led to an “operational taxonomic unit” gap in our understanding of tuna ecology. These rarely-caught intermediate assemblages have remained inadequately described due to limited sampling across their wide range of coastal and oceanic habitats. This study examined the spatiotemporal dynamics of larval and juvenile tunas collected in the northern Gulf of Mexico from January to September, 2011, as part of the Offshore Nekton Sampling and Analysis Program. The species composition, abundance, and distribution of the family Scombridae collected from the sea surface to 1500 m depth were characterized with respect to depth of occurrence, time of year, and in relation to mesoscale oceanographic features. Generalized additive models were used to investigate the relationships between several environmental parameters and scombrid abundances in the epipelagic waters of the oceanic Gulf. Highest catches of the family Scombridae were associated with Common Water, nighttime sampling, and seasonality. Species-specific environmental preferences in Gulf Common Water were identified for the most-abundant species collected in this study, Euthynnus alletteratus (little tunny or false albacore) and Thunnus atlanticus (blackfin tuna). Euthynnus alletteratus abundances were highly seasonal, associated with offshore waters, and marginally correlated with salinity. Thunnus atlanticus abundances were strongly seasonal, correlated with salinity, and marginally correlated with day/night cycle and distance to 200-m isobaths (i.e., shelf break). Aspects of juvenile scombrid ecology investigated here will inform management and conservation efforts for this highly important taxon in continental shelf and oceanic environments