Influence of oceanographic conditions on the distribution and abundance of blackfin tuna (Thunnus atlanticus) larvae in the Gulf of Mexico

Information on early life history of economical important fisheries stocks are required to accurately estimate their population status. This study investigated blackfin tuna (Thunnus atlanticus) larvae distribution over six summers (2007-2011, 2015) in the northern Gulf of Mexico. Blackfin tuna were commonly observed and widely distributed in surface waters with frequency of occurrence ranging from 48% (2008) to 92% (2011). Inter-annual variability in density was observed with highest mean density recorded in 2009 (17.2 larvae 1000 m−3) and lowest mean density in 2015 (2.2 larvae 1000 m−3). Density also varied between months with higher overall mean density observed in July (9.2 larvae 1000 m−3) compared to June (4.3 larvae 1000 m−3). Generalized additive models (GAMs) based on presence/absence and density of blackfin tuna larvae determined that this species was present in areas of intermediate salinity (31-36) and higher sea surface temperature (SST > 29 °C). Blackfin tuna larvae were also strongly associated with convergent zones near the Loop Current and anticyclonic eddies. Environmental conditions deemed to be favorable from GAMs (salinity, SST and sea surface height) were combined with environmental data in 2011 and 2015 to predict the suitable habitat of blackfin tuna larvae from the outer continental shelf into oceanic waters (areas ≥100 m isobath). The amount of highly suitable habitat ( >10 larvae 1000 m−3) in 2011 and 2015 varied between months (June 6%, July 51%); however, blackfin tuna larvae were predicted to occur at similar locations in surface waters along the continental slope and at the margin of the Loop Current. Overall, the results highlighted the importance of mesoscale features and oceanographic conditions on the distribution and abundance of blackfin tuna larvae.