ECOLOGICAL STOCKS OF THE JACK MACKEREL (TRACHURUS-SYMMETRICUS-MURPHYI NICHOLS) IN 3 FISHING AREAS OFF CHILE, DETECTED THROUGH COMPARISON OF THE PARASITE FAUNA AND MORPHOMETRY

Among methods traditionally used for stock discrimination, neither the parasitological nor the morphometric have been employed in fish resources of Chile. From the comparative analysis of the metazoan parasite fauna and the morphometry of jack mackerels, the existence of ecological stocks is inferred. They suggest a geographical differentiation due to isolation accumulated along the fish ontogeny, and longitudinal seasonal migrations of fishes. Data consisted in monthly samples of 50 specimens taken along 1990 from purse seine vessels operating at coastal fishing areas nearby Iquique and Talcahuano. Additional 183 fishes were taken in 5 samples collected 150 to 250 nautical miles off Constitucion, between march and april, 1990. A total of 2,393 parasite individuals belonging to 14 taxa were collected from 29 samples comprising 1,383 fishes examined. The parasite fauna of fishes from Iquique and Talcahuano showed quantitative differences only, though significant and consistent along the year. Some of these are due to differences in the body size of fishes in the samples, but others are attributable to the geographic origin of the samples. Patterns of temporal and geographic differences suggest that offshore jack mackerels migrate towards the coastal zone of Talcahuano in winter, with smaller fishes first, and later with increasingly larger fishes, up to midsummer. No such pattern of migration was detected in fishes from Iquique.