Temporal shifts in the abundance and preferred habitats of yellowfin and bigeye tuna larvae in the Gulf of Mexico

Abstract

The influence of environmental conditions on the relative abundance of Thunnus albacares (yellowfin tuna) and Thunnus obesus (bigeye tuna) were investigated to determine the extent of the early life stage suitable habitat of these species in the Gulf of Mexico (GoM). Thunnus albacares and T. obesus larvae were commonly found (31–50% frequency of occurrence per year) in the northern GoM (26–28°N, 91–96°W), and a significant intra- and inter-annual variability in abundance of T. albacares and T. obesus was observed with higher abundance recorded in July surveys (1.3 larvae 1000 m−3 for both species) and during the Summer 2009 (1.9 and 1.7 larvae 1000 m−3, respectively). Generalized additive models (GAMs) indicated that larvae of T. albacares and T. obesus were more common and at higher abundance in water masses with moderate to high salinity (28–36), high temperature (29 °C), positive sea surface height. Species-specific environmental preferences determined with GAMs were then combined with summer environmental data over eight years (2007 to 2015) to predict the spatial coverage of suitable habitat of both species in regions beyond the 100-m isobath. Habitat suitability predictions indicated that the location and extent of highly suitable habitat of T. albacares and T. obesus larvae varied across years with the highest areal coverage in 2015 (70%) and 2010 (73%), respectively. Both T. albacares and T. obesus larvae were more commonly observed and at higher abundance off the continental slope and at margins of the Loop Current and associated warm-core eddies in the northern GoM. Because changes in environmental conditions influenced the spatio-temporal distribution of T. albacares and T. obesus larvae, habitat suitability models are valuable tools for identifying critical areas of the GoM inhabited by tuna larvae and this information can also be used to assess potential impacts of natural and anthropogenic disturbances on the recruitment and population dynamics of tunas.