the humboldt current system of northern and central chile - figema

THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILEPeru (Uribe & Blanco 2001). It has long been recognised that natural scallop stocks vary togetherwith ENSO variations, mainly because settlement of small settlers (spat) is strongly favoured duringEN events (Narvarte et al. 2001). Due to this relationship, the local scallop industry is affected ina positive way by EN, which can lead to an increase in spat collection by >300% (Illanes et al.1985). In a research project on the effect of environmental factors on scallop culture, data of watertemperature, gonad indices, larval abundance and recruitment (spat collection) were gatheredbetween 1981 and 1984 in Tongoy Bay (Illanes et al. 1985). The EN event led to a temperatureincrease of 2°C above the pre- or post-EN levels at the sea surface and of 2.5°C at the bottom(20 m). During the EN period, the Gonad Index of adults registered a maximum (25) and a minimum(6.8) with a massive evacuation of gametes, a situation never observed during normal years (Illaneset al. 1985). Similar observations were made in southern Peru by Wolff (1988), who concludedthat A. purpuratus is a continuous spawner with spawning peaks during late austral summer andautumn (February–March). Under the unusually high water temperatures during EN 1982–1983(2–2.5°C above the normal temperatures), the recuperation time between two spawnings wasshortened, indicating that maturation was accelerated and spawning probably intensified under theseconditions. This interpretation was confirmed by the highest larval concentration found within theperiod. Wolff (1988) stated that it is not clear along the Peruvian coast that past EN favoured thescallops stocks. The EN 1972 apparently did favour stocks, as catches were significantly higher thanduring the 3 yr before and after this event, but the weaker EN 1976 did not have the same effect.In 1979, which was a ‘normal’ year, the catches still exceeded the catches of 1972. Limo (in apersonal communication to M. Wolff) reported enormous numbers of A. purpuratus during thestrong EN 1925 in Ancon Bay, north of Lima. In order to reduce the dependency on natural variationsin supply of small recruits, intense efforts have been undertaken to produce settlers in the laboratory(Uriarte et al. 2001), but this only satisfies part of the requirements for scallop spat. The fact thatnatural spat is still obtained at much lower costs than spat produced in the laboratory may haveled to the strong increase in spat collectors observed during recent years in Tongoy Bay (Figure 28).Possibly, the decreasing spat collection efficiency between 1998 and 2001 (when the total numberof spat collectors in the bay exceeded 2.5 million bags) is indication that the carrying capacity isreached and that spat collectors are starting to compete for the available settlers.Culture of Gracilaria chilensis in northern Chile is mainly developed on shallow soft bottomsin sheltered parts of the bays (e.g., Pizarro & Santelices 1993). Since sheltered bays are relativelyscarce along the cost of northern and central Chile, aquaculture of this seaweed in this area doesnot reach the amounts harvested in southern Chile. Edding & Blanco (2001) observed a decreasein productivity and yield of ‘agar’ from G. chilensis cultured in Region IV (29°59′S) during EN1997–1998. This may be more related to the decrease in nutrient concentrations and increase ofvisibility instead of the higher water temperatures. Furthermore, these authors cited González(1998), who reported that increased wave action during EN resulted in an important reduction ofbiomass. Growers of G. chilensis in Region IV also reported heavy damage to culture fields onshallow subtidal soft bottoms caused by storms during EN (R. Rojas personal communication).However, Santelices et al. (1984) stated that recovery of Gracilaria sp. after storms is unexpectedlyfast due to regrowth of thalli from the portions buried in the sand. Overall, the production ofG. chilensis in northern Chile does not seem to be severely affected by ENSO, but is ratherdetermined by stock density and harvesting frequency (Pizarro & Santelices 1993). The relativelylimited interannual variability in extracted and cultured biomass (Figure 28) further supports thesuggestion that management rather than environmental conditions drive the production of G. chilensisin northern Chile.During recent years first attempts have been made to culture large kelps from northern andcentral Chile (e.g., Edding et al. 1990, Edding & Tala 2003) in order to satisfy the growing needsof the abalone culture. This is considered particularly important since EN can have dramatic impacts293