Direct and indirect effect on the high seas fisheries on the marine mammal populations in the northern and central patagonian coast

CRESPO, ENRIQUE ALBERTO; PEDRAZA, SUSANA; DANS, SILVANA LAURA; KOEN ALONSO, MARIANO; REYES, LAURA MARINA; GARCÍA, NÉSTOR ANÍBAL; COSCARELLA, MARIANO ALBERTO; SCHIAVINI, ADRIÁN CARLOS MIGUEL

Dartmouth

Simposio; NAFO/ICES Symposium of the Role of Marine Mammals in the Ecosystem; 1995

NAFO/ICES

Interaction between marine mammals and fisheries were monitored in the Patagonian coast since 1989. The national fleet in the area is composed of approximately 190 fishing vessels (80% trawlers; 15% jiggins; 5% longliners). The fleet operates the whole year from 7 different harbours between Isla Escondida and Golfo San Jorge (80.000 nm2). The most important target species include the hake (M. hubbsi), the squid (I. argentinus) and the shrimp (P. muelleri), while several tons of fish are discarded. The dusky dolphin (L. obscurus), the Commerson´s dolphin (C. commersonii) and the southern sea lion (O. flavescens) are incidentally captured frequently. The dolphins get entangled mostly in mid-water trawls at night, while sea lions do it in any kind of trawl. Mortality rates preliminary obtained are 70-200 dusky dolphins (70% mature females) and 170-480 sea lions per year (mostly males; figure estimated to be 1-2% of the population size in the area). Feeding habits of top predators (including size of the prey) and fish catch and by-catch of the fishery was also studied. Dusky dolphins in the area prey mostly on anchovies (10-15 cm) and squid (3-18 cm), while hake was the most important for Commerson´s dolphins (5-13 cm) and male southern sea lions (10-45 cm) among other species. Squid is also an important prey for sea lions (15-33 cm) overlapping in size with the commercial sizes of the fishery. A combination of operational and specific effects were detected on the populations. While at present times, mortality rates seem to be low and that there is not enough evidence of competition for prey species, a concern exists about the large amounts of fish (particularly hake) discarded by the fishery.