Abstract

The jack mackerel fishery is one of the most important resources on the South Eastern Pacific Ocean off Chile, with landings higher than 3 million tonnes between 1990 and 1996. During 1997-1998, remarkable changes occurred in the length structure of jack mackerel catches, as juveniles (<26 cm FL) dominated the fishing grounds. That was attributed to the environmental effects of the 1997-98 El Niño on the feeding grounds of the jack mackerel off central-southern Chile. Anomalous sea surface temperatures were first detected in June 1997 and persisted into 1998. The response of the incidence of juveniles lagged one year after the ENSO phenomenon affected central-southern Chile, whereas there was a direct relationship between the proportion of juveniles and the intrusion of the 15°C isotherm towards the south. This isotherm reached its most southerly distribution in 1997-98, as a consequence of the El Niño. Jack mackerel is an oceanic and highly migrating species, so we propose that El Niño conditions affected the migratory pathway of the juveniles. It is postulated that the restoration of the nursery habitat north of 30°S may be delayed by more than 3-4 years. New juveniles will dominate in northern areas in the short-term, whereas the juveniles that migrated to southern areas during 1997-1999 are not expected to return back north. At present, the real situation of the stock is far from certain, but we think that environmental impacts associated to the El Niño can not be overlooked when planning the management of the jack mackerel fishery. © 2001 Published by Elsevier Science Ltd.