Use of Oceanographic Data to Improve Atlantic Bluefin Tuna Management Decision Making
Barbara
A
Muhling, NOAA-NMFS, barbara.muhling@noaa.gov
(Presenting)
Mitchell
Roffer, ROFFS, roffers@bellsouth.net
John
T
Lamkin, NOAA-NMFS, john.lamkin@noaa.gov
Frank
E
Mueller-Karger, University of Massachusetts, fmullerkarger@umassd.edu
William
J
Richards, NOAA-NMFS, bill.richards@noaa.gov
Andrew
Bakun, University of Miami - RSMAS, abakun@rsmas.miami.edu
Northern bluefin tuna (Thunnus thynnus) support significant recreational and commercial fisheries across the Atlantic, however biomass of this species has declined markedly over previous decades. The Gulf of Mexico is the only known bluefin tuna spawning ground in the Western Atlantic, with peak spawning activity in May. Annual spring plankton surveys targeting larval bluefin have been completed across a grid of stations in the northern Gulf since 1977, and the resulting ichthyoplankton index has been used to refine bluefin tuna population estimates, which are critical to understanding the dynamics of this valuable species. However, as few bluefin tuna larvae are typically caught in the spring surveys, variance in the ichthyoplankton index is currently high.
The goal of this study is to reduce the variance in the estimates of adult Atlantic bluefin tuna spawning stock abundance in the Gulf of Mexico by developing spawning site habitat classification and catchability indices of the larvae. These will be derived from the innovative use of several earth orbiting satellites, and by the use of multivariate and spatial statistics to develop enhanced biological and oceanographic indicators for the Gulf of Mexico. While the catchability indices will be used in developing indices for the population analyses, the habitat classification will aid in developing models forecasting where concentrations of larvae are likely to occur, leading to an adaptive sampling strategy.
Finer-scale sampling on the spring surveys, concentrating on particular oceanographic features, will also allow us to better define relationships between bluefin tuna larvae and their environment. Accurate and efficient sampling of chosen features will be made possible by access to high-resolution satellite imagery. This refined sampling strategy will be trialed on the spring 2008 sampling cruise.
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