The jack mackerel fishery and el nin˜o 1997–98 effects off

Progress in Oceanography 49 (2001) 597–617 www.elsevier.com/locate/pocean

The jack mackerel fishery and El Nino 1997–98 effects off ˜ Chile
´˜ Dagoberto F. Arcos *, Luis A. Cubillos, Sergio P. Nunez
Instituto de Investigacion Pesquera, Casilla 350, Talcahuano, Chile ´

Abstract The jack mackerel fishery is one of the most important resources on the South Eastern Pacific Ocean off Chile, withlandings 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 Nino on the feeding ˜ grounds of the jack mackerel off central–southern Chile. Anomalous sea surface temperatures werefirst 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 Nino.Jack mackerel is an ˜ oceanic and highly migrating species, so we propose that El Nino 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 1997–1999are 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 Nino can not be overlooked when planning the management of the jack mackerel fishery.  2001 ˜ Published by Elsevier Science Ltd.

Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . 598

2. Data and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602 2.1. Environmental data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602 2.2. Fishery and biological data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . 603

* Corresponding author. Tel.: +56-41-584820; fax: +56-41-583939. E-mail address: inpesca@inpesca.cl (D.F. Arcos).

0079-6611/01/$ - see front matter  2001 Published by Elsevier Science Ltd. PII: S 0 0 7 9 - 6 6 1 1 ( 0 1 ) 0 0 0 4 3 - X

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D.F. Arcos et al. / Progress in Oceanography 49 (2001) 597–617

3. Results . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603 3.1. Environmental variability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603 3.2. Length-structure changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 606 4. Discussion . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 608

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 616 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 616

1. Introduction Chilean jack mackerel,Trachurus symmetricus murphyi (Nichols) is a medium-sized pelagic fish that inhabits the southern Pacific Ocean. In the early 1970s, it was believed that this species occurred only in the coastal waters of Chile and Peru. However, the activity of Russian fleet and their research experience during the late 1970s and the 1980s in the oceanic waters from South America to New Zealand, showed that the...