AERIAL SURVEY OF GIANT BLUEFIN TUNA, THUNNUS-THYNNUS, IN THE GREAT BAHAMA BANK, STRAITS-OF-FLORIDA, 1995

Aerial surveys were conducted daily from 19 May to 9 June 1995 to docu ment the apparent abundance and migration behavior of giant bluefin tu na, Thunnus thynnus, over the Great Bahama Bank region of the Straits of Florida. Our objectives mere to conduct an aerial assessment of gia nt bluefin tuna in this region and to compare our results with previou s aerial surveys conducted in the 1950's and 1970's. Two professional bluefin spotter pilots flew 70-nmi transect surveys along ''Tuna Alley '' as well as surveys into adjacent areas in search of bluefin tuna. T he present study area was broader than that surveyed in the 1970's, wh ich consisted of repeated flight tracks, each 1 nmi, across Tuna Alley at a point just south of South Cat Cay. Spotter aircraft carried a da ta acquisition system consisting of a global positioning system (GPS), a laptop computer, and a 35-mm camera to photograph schools. A total of 839 giant bluefin tuna were documented, within range of totals coun ted in the 1974-76 surveys (368-3,125 bluefin tuna). Single fish and l oosely aggregated schools of up to 100 fish were seen travelling stead ily north along the western flank of the Great Bahama Bank. They did n ot engage in feeding, smashing, or cartwheeling behaviors that are exh ibited in New England waters. AU bluefin tuna appeared to be ''large g iants,'' weighing an estimated 227 kg and over. There is little inform ation documenting the origins and previous locations of giant bluefin tuna travelling along the Great Bahama Bank; therefore the use of dire ct counts of bluefin tuna in this region as an index of spawning bioma ss would require further documentation.