The jack mackerel fishery and El Nino 1997-98 effects off Chile

The jack mackerel fishery is one of the most important resources on the Sou th Eastern Pacific Ocean off Chile, with landings higher than 3 million ton nes between 1990 and 1996. During 1997-1998, remarkable changes occurred in the length structure of jack mackerel catches, as juveniles (< 26 cm FL) d ominated the fishing grounds. That was attributed to the environmental effe cts of the 1997-98 El Nino on the feeding grounds of the jack mackerel off central-southern Chile. Anomalous sea surface temperatures were first detec ted in June 1997 and persisted into 1998. The response of the incidence of juveniles lagged one year after the ENSO phenomenon affected central-southe rn Chile, whereas there was a direct relationship between the proportion of juveniles and the intrusion of the 15 degreesC isotherm towards the south. This isotherm reached its most southerly distribution in 1997-98, as a con sequence of the El Nino. Jack mackerel is an oceanic and highly migrating s pecies, so we propose that El Nino conditions affected the migratory pathwa y of the juveniles. It is postulated that the restoration of the nursery ha bitat north of 30 degreesS may be delayed by more than 3-4 years. New juven iles will dominate in northern areas in the short-term, whereas the juvenil es that migrated to southern areas during 1997-1999 are not expected to ret urn back north. At present, the real situation of the stock is far from cer tain, but we think that environmental impacts associated to the El Nino can not be overlooked when planning the management of the jack mackerel fisher y. (C) 2001 Published by Elsevier Science Ltd.