Incidental catch associated with swordfish longline fisheries in the south-west Atlantic Ocean

Abstract

This paper describes the composition of the harvest by species of two vessels operating with two different pelagic longline systems aimed at swordfish (Xiphias gladius). Four zones were surveyed in the Uruguayan EEZ and international waters in the south-western Atlantic. Data were collected by observers on board who recorded the number of individuals in each of the species caught. In all, 50 species were caught, of which 15 were cartilaginous fish, 27 were teleosts and eight were ‘non- fish’ species (birds, mammals and turtles). The most abundant species were blue shark (Prionace glauca) (43%), swordfish (27%) and albacore tuna (Thunnus alalunga) (9%). The abundances of blue shark and of swordfish differed significantly between the two rigging systems and among the four zones. The catch was classified into three marketing groups: primary marketing (swordfish and high-price tuna), secondary marketing (non-target species but marketable) and discards (with no commercial value). In terms of numbers, the first two groups represented between 91% and 72% of the species collected. This percentage may vary if the catch is analysed by weight, as only part of the carcass and shark fins are used.

Resumen. Se describe la composición por especies de la captura de dos buques que operaron con dos sistemas diferentes de palangre pelágico dirijido a la extracción de pez espada (Xiphias gladius). Se relevaron quatros áreas que abarcaron la ZEE uruguaya y aguas internacionales en el O. Atlántico. Los datos fueron colectados a bordo por observadores, registrando la captura en número de la totalidad de las especies. Se contabilizó un total de 50 especies capturadas, de las cuales 15 corresponden a peces cartilaginosos, 27 a peces óseos y 8 a ‘non-pisces’ (aves, mamíferos y quelonios). Las especies más representadas fueron el tiburón azul (Prionace glauca) (43%), seguida por pez espada (27%) y albacora (Thunnus alalunga) (9,0%). La presencia de tiburón azul y pez espada mostró diferencias significativas comparando los dos sistemas de construcción del palangre y las zonas. Se clasificó la captura en tres grupos de comercialización: comercialización primaria (pez espada y atunes de elevado valor), comercialización secundaria (especies diferentes de la objetivo pero comercializables), y decarte (sin valor comercial). Las dos primeras acumularon entre el 91% y 72% de las piezas capturadas. Este porcentaje puede variar si se analiza la captura en peso, ya que de los tiburones se aprovechan las aletas y solamente parte de las carcasas.