MIAMI — Tuna and billfish, such as sailfish and marlin, might be more vulnerable to overharvest because their Atlantic habitat is shrinking. A study led by Eric Prince of NOAA Fisheries' Southeast Fisheries Science Center in Miami shows that a large area of oxygen-poor water in the eastern tropical Atlantic is expanding, forcing these fish into oxygen-rich, shallower waters where they are more likely to be caught.
The study, in the November edition of Fisheries Oceanography, has major implications for scientific stock assessments performed by the International Commission for the Conservation of Atlantic Tunas. Cramming more fish into a shrinking habitat yields high catch rates, which can skew estimates of population abundance and lead to even more overfishing.
"If you don't account for that difference in density, it gives you a false signal," Prince said.
Prince and colleagues from the University of Miami and the Billfish Foundation outfitted 79 sailfish and blue marlin in the western North Atlantic off South Florida and the Caribbean and in the eastern tropical Atlantic off the coast of West Africa with satellite pop-up tags. The tagging data showed that fish would swim as close to the surface as necessary to find oxygen-rich waters. They avoided areas of low oxygen.
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