Scientific Journal Article Summary

Oceanographic preferences of Atlantic bluefin tuna, Thunnus thynnus, on their Gulf of Mexico breeding grounds
Steven L. H. Teo, Andre M. Boustany, Barbara A. Block
Marine Biology 152:1105–1119

In marine fish, such as Atlantic bluefin tuna, the location and timing of spawning determine the environmental conditions experienced by the adults and larvae.  Optimal conditions can maximize reproductive success.  To determine the environmental preferences of bluefin breeding in the Gulf of Mexico, position data of electronically tagged fish were compared with oceanographic data collected by satellites.  A model was developed to test habitat use for ten environmental parameters, including 1) bathymetry (i.e., depth), 2) bathymetric change, 3) sea surface water temperature (SST), 4) SST gradient, 5) chlorophyll concentration (an indicator of productivity), 6) chlorophyll gradient, 7) sea surface height, 8) eddy kinetic energy (i.e., a measure of water flow variability), 9) wind speed, and 10) current speed.

Atlantic bluefin tuna breeding behavior was concentrated in the western Gulf of Mexico (Figure 1) but also occurred in the frontal zone of the Loop Current, the major current feature in the Gulf. Breeding areas used by bluefin tuna were significantly associated with bathymetry, SST, eddy kinetic energy, chlorophyll concentration, and wind speed. Water temperature was the most important environmental parameter, with the bluefin preferring moderate temperatures (75-80ºF) to ensure a warm area for the larvae without causing too much heat stress to the spawning adults. Bluefin tuna also exhibited significant preference for continental slope waters (~2 miles deep), moderate eddy kinetic energy, low chlorophyll concentrations, and moderate wind speeds. The depth and eddy kinetic energy preferences are likely related to a desire to spawn in eddies, which have increased retention of larvae and their prey and have been hypothesized to increase larval survival.  Low chlorophyll indicates low productivity, which would be beneficial since the area would be less attractive to predators.  Moderate wind speed is thought to increase contact between larvae and their prey, which in turn would improve feeding and growth rates of larval bluefin.

The habitat use and preference patterns of breeding bluefin tuna revealed through this study can be used to develop models to estimate likely breeding areas in an ever-changing environment. Although directed fishing for bluefin tuna in the Gulf of Mexico has been prohibited since 1982, other fisheries catch bluefin incidentally while targeting other species. A habitat model developed based on the oceanographic preferences determined through this study could be used to design a restricted time-area closure to fishing in the Gulf to reduce incidental mortality of bluefin, in turn contributing to the recovery of the severely depleted western Atlantic bluefin tuna population.

Figure 1. Spatial distribution of breeding Atlantic bluefin tuna in the Gulf of Mexico.  Warmer colors indicate a greater concentration of fish.

Download full text.

back to publication list