Pesca e ecologia da albacora bandolim (Thunnus obesus) no oceano atlântico tropical

Abstract

Bigeye is currently considered the most valuable target species of tuna longline fisheries in the Atlantic Ocean. Thus, the history of bigeye tuna longline fisheries in the Atlantic Ocean between the years of 1956-2012 was reviewed, and the relationships between bigeye tuna fishing core and environmental conditions and size composition were analyzed. Longline catch represents 64% of total catch in the period of 1956-2012. The Asian fleets are the main operating in the Atlantic Ocean, corresponding to 74% of the bigeye tuna catches. The main fleet operating is the Japanese with 1.1 million tons (47%), followed by China- Taipei and Korea with 19% and 8%, respectively. The Brazil occupies the 7th position regarding production (catch) of bigeye tuna, with approximately 49.000 t (2.2%). The relationship between capture and oceanographic conditions displayed better scenery in zones with SST between 24 - 26ºC, lower thickness of optimal temperature layer (~50 m) and when this top layer is located in the depths between 100 and 250 m. Others important characteristics defining the fishing grounds are: the top of thermocline depth occurring between 20 and 55 m, temperature of the top of thermocline depth between 24 and 25ºC and temperature of the base of thermocline between 17ºC and 19ºC. The bigeye tuna size (fork length) ranged from 40 to 222 cm with a mode value in the sizes class between 120 and 160 cm and mean size of 138.1 cm ± SD 28.9 cm. Proportions of immature bigeye tuna (< 110 cm) in the catches was approximately 0.18 for all data. However, proportions of immature for quarters showed greater value than 0.18, with the 3rd and 4th quarters presenting the bigger values, 0.20 and 0.24, respectively. Larger lengths were associated with SST between 23 and 27ºC, temperature of the base of thermocline better than 18.5ºC and top of the thermocline depth occurring between 20 and 45 m. The immature bigeye tuna are associated and occurred in the regions with high SST’s between 26 and 29ºC, temperature of the base of thermocline between 16 and 17.5ºC and temperature of the top of thermocline depth greater than 22ºC.