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Blackfin tuna, Thunnus atlanticus, is the target species of a handline artisanal fishery off northeastern Brazil in September–January, but it is also caught by anglers and as by-catch in industrial fisheries. The population structure, morphometric relationships, mortality, reproduction, and fishery dynamics were studied during 2 fishing seasons (1996 and 1997). The maximum length and weight observed were 87 cm FL and 10 kg Wd, respectively. Males were larger and predominant (1.9:1). The length at 50% maturity was 49.8 cm FL for females and 52.1 cm FL for males. This species uses the area for reproduction, although a spawning peak was not observed. The length at first capture (58.1 cm FL) was higher than the length at 50% maturity. The total, natural, and fishing mortality rates were 2.34, 0.94, and 1.40 year–1, respectively. The total length-fork length and the total length-standard length relationships were TL = 1.35369 + 1.0462 FL and TL = 6.37742 + 1.0544 SL, respectively (sexes grouped). The length-weight relationship estimated for both sexes was Wd = 0.00003 FL2.8569. Annual catches decreased from 154 t year–1 in the 1970s to 33.5 t year–1 in the 1990s. It seems that there was not much change in the structure of this stock after 30 years, but the lack of a proper collection system of catch data and the increasing interest in recreational fisheries raise reasons for concern. RESUMEN El Atun aleta negra, Thunnus atlanticus, es capturado por una pesqueria artesanal en el noreste de Brasil de septiembre a enero, pero tambien por pescadores recreacionales y como fauna acompanante en pesquerias industriales. La estructura de la poblacion, relaciones morfometricas, mortalidad, reproduccion y dinamica pesquera fueron estudiadas durante dos temporadas de pesca (1996 y 1997). La longitud y el peso maximos observados fueron 87 cm FL y 10 kg Wd, respectivamente. Los machos fueron mayores y predominantes (1.9:1). El tamano al 50% de madurez fue 49.8 y 52.1 cm FL para machos y hembras, respectivamente. Esta especie usa la region para reproduccion, aunque un pico de desova no fue observado. El tamano en la primera captura (58.1 cm FL) fue mas alto que el tamano al 50% de madurez. La mortalidad total, natural, y por pesca fueron 2.34, 0.94 y 1.40 ano–1, respectivamente. Las relaciones longitud total-longitud furcal y longitud total-longitud estandar fueron: TL = 1.35369 + 1.0462 FL y TL = 6.37742 + 1.0544 SL, respectivamente (sexos agrupados). La relacion peso-longitud estimada para ambos los sexos fue de Wd = 0.00003 FL2.8569. Las capturas anuales disminuyeron de 154 t ano–1 en la decada de los 70s a 33.5 t ano–1 en la decada de los 90s. Los resultados parecen indicar que no ha habido mucho cambio en la estructura de este estoque despues de treinta anos, pero la carencia de un sistema apropiado de la obtencion de datos de captura y el interes de las industrias pesqueras recreacionales son motivo de preocupacion.

Fishery and Biology of Blackfin Tuna Thunnus atlanticus off Northeastern Brazil