Direct Assessment of Juvenile Atlantic Bluefin Tuna: Integrating Sonar and Aerial Results in Support of Fishery-Incident Surveys

SUMMARY There is a clear need for direct assessment for Atlantic bluefin tuna (Thunnus thynnus, ABFT), including formulation of experimental designs and pilot surveys for abundance estimation. In the western Atlantic, aerial surveys are highly feasible for juvenile ABFT because of their surface availability. Our goals are to design, implement, and analyze a fisheries-independent survey of juvenile ABFT. We used aerial imagery to determine the school’s surface shape and to enumerate bluefin tuna visible in the upper few meters of the water column and sonar data provided information on school height. By integrating acoustic and aerial data we can estimate school biomass and aggregation behavior. In 2015 we plan to use a marine hexacopter to obtain more highly resolved aerial images of schools, with improved geo-rectification required for automated target recognition and objective counts of individuals. Although not without challenges, the analytical techniques we’re developing will provide more objective, multidimensional information on ABFT schools. Direct assessment also offers a means of tracking shifts in coastal distribution of highly mobile ABFT, especially as traditional indices of abundance may no longer be appropriate. RESUME