versión On-line ISSN 0717-7178
Investig. mar. v.30 n.1 supl.Symp Valparaíso ago. 2002
Climate Variability and Pelagic
Fisheries in the South-Eastern Pacific*
1Escuela de Ciencias del Mar, Universidad Católica de
Valparaíso, Casilla 1020, Valparaíso, Chile,
2Instituto de Fomento Pesquero, Huito 374,
Valparaíso, Chile, E-mail: email@example.com
One of the most productive systems is the Humboldt current and, as other eastern boundary systems, it shows a low diversity of pelagic species with abundant but variable stocks. In general, its variability is associated with the exploitation intensity and changes in the environmental conditions. This way, together with China, Peru and Chile are the most important fishing countries of the world, with pelagic resources representing more than 90% of landings.
Pelagic fisheries were initially based on common sardine (Strangomera bentinki) in the centre-south of Chile and mainly on anchovy (Engraulis ringens) in Peru and northern Chile. These species were mostly distributed within 60 nm of the shore, they are small in size, have a short life span and high fecundity. In the mid 1970s these fisheries collapsed, being replaced by sardine (Sardinops sagax) in northern Chile and Peru, and by jack mackerel (Trachurus murphyi) particularly in the centre-south of Chile. These species are larger and longer lived, have lower fecundity and a more oceanic distribution, particularly the jack mackerel. These fisheries showed a drastic decrease in yields (CPUE) after 1985, while at the same time a remarkable recovery of the common sardine and anchovy fisheries was observed.
Common sardine and mainly anchovy landings show decreases associated with El Niño events, particularly the 1972-1973 phenomenon (Fig.1). The El Niño represents an interannual climatic variability and produces effects in abundance (for recruitment and growth), distribution (horizontal and vertical) and aggregation (schools and strata) of resources. Accoustic cruises classified according to NOAA categorization (cold and warm episodes by season), show the highest anchovy biomasses associated with cold and normal events, and a distribution area that can quintuple; during El Niño the biomass diminishes and contracts toward the coast and the south, and it is deepened, presenting disintegrated echo-traces.
Fig. 1 Anchovy landings in Peru and northern Chile between 1950 and 1999. The arrows indicate the El Niño events and the intensity.
However, the non-recovery of these fisheries after 1976 was coincident with the drop of the Southern Oscillation Index (SOI) and the presence of a long-term warm period reflected in the sea surface temperature (SST) of Chile and Peru, after accounting for the effects of fishing effort (Fig. 2a). Warm periods and particularly the regime shift observed after 1976 would be unfavourable to the anchovy, while favouring the sardine (Fig. 2b), on which important fisheries were developed in northern Chile (maximum 2.5 million tons in 1983) and Peru (maximum 3.5 million tons in 1988). In the centre-south of Chile the jack mackerel landings also increased with this regime shift, associated with the development of a remarkable fishing effort, reaching up to 4 million tons in 1995. However, the catch per unit effort (CPUE), after an important increase during this long-term warm period, showed a decline beginning in 1987 (Fig. 3). Accoustic information available from 1990 shows that, during autumn of the El Niño the jack mackerel increase their distribution area, while during La Niña they are more aggregated toward the south. On the other hand, during cold and normal years the jack mackerel school size inside the cluster is bigger than the individual schools, while during the El Niño events the situation is reversed.
Fig. 2 EOF time series analysis of catch, fishing effort, SST and SOI for anchovy; and recruitment, biomass, SST and upwelling index for sardine.
On the other hand, the Chilean artisanal swordfish (Xiphias gladius) fishery, predator of jack mackerel and hoki (Macruronus magellanicus), shows a remarkable decrease in yield after 1987, associated with the re-establishment of similar cold conditions to those observed before 1976 (Fig. 4). Contrarily, before this new regime shift observed after 1987, the hake (Merluccius gayi) fishery of central Chile shows a remarkable recovery (Fig. 5).
This high variability is associated with atmospheric pressure fluctuations between the Eastern and Western Pacific, reflected in the SOI. Nevertheless, the new regime shift observed after 1987, in the coastal SST and in the catches of these resources, is not clearly observed in this South Pacific climatic index.
It is necessary to point out that a climatic regime shift is also observed in the North Pacific in 1976-1977, and this change produced great consequences in the marine ecosystem. A regime shift was also identified in 1989 in some components of this ecosystem, but it doesn't reflect a return to conditions prior to 1977. Also, although the shift of 1989 is observed with relative clarity in biological records, it is not reflected in the Pacific climatic indices, like the Pacific Decadal Oscillation (PDO).