the humboldt current system of northern and central chile - figema

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MARTIN THIEL ET AL.the risk that fishermen continue fishing on a weakened population, perhaps producing its collapseto a degree where recovery is severely compromised. Additionally, the distribution of fishermenalong the coast within each region in general is not well adjusted to its spatial productive variability,thus creating great differences of income along the coast, with fishermen’s organisations locatedat productive sites getting increasingly richer, and others at unproductive sites (as shown withharvest in AMERBs in Figure 24) getting increasingly poorer, which could be a source of conflicts(Gelcich et al. 2005, Stotz & Aburto 2006). The challenge is to advance to an integral managementstrategy in which fishermen, instead of rotating between fishing zones along the coast, rotatebetween fisheries of different resources or among other related activities (processing, tourism, etc.)in order to produce income during years or months of poor production. This means a change froma specialist to a generalist strategy, but with very strict control of their numbers, such that they arewell adjusted to local production levels. Complementary stock enhancement, using biological andecological knowledge and aquaculture experience, might help to mitigate natural fluctuations (Stotzet al. 1992, Zamora & Stotz 1994, Pacheco & Stotz 2006). In order to avoid the risk of increasedfishing pressure (caused by restricting movements of fishermen) on already weakened populations,the establishment of a network of small reserves along the coast should be considered, which shouldalso aid in reducing natural recruitment variability (see also Stotz & Aburto 2006).Bioeconomic aspects of industrial crustacean fisheriesAn important crustacean bottom-trawl fishery exists in northern and central Chile, particularlybetween Regions II and IV. This fishery, which includes the nylon shrimp (Heterocarpus reedi),yellow squat lobster (Cervimunida johni) and the red squat lobster (Pleuroncodes monodon), isconducted on the continental shelf at depths ranging from ~100 to 600 m. The exploitation of theseresources began in the 1950s as fauna accompanying catches of hake Merluccius gayi and wassubsequently developed into a fishery specific for these crustaceans (Arana & Nakanishi 1971,SUBPESCA 1999a,b). A growth phase for these fisheries occurred between 1958 and 1968, duringwhich annual landings of nylon shrimp reached 11,000 t. Subsequently, landings declined to lessthan 3000 t in 1979. Between 1980 and 1986 landings remained below 4000 t, except for 1983,when landings exceeded 6000 t. The last period is interesting in its analysis since it coincided withthree fundamental factors: (1) from 1979 to 1982 the exchange rate (Chilean peso/U.S. dollar) was39 Chilean pesos/U.S. dollar, which produced a depressive economic effect, resulting in the collapseof fisheries companies; (2) in 1983 the occupation of new fishing grounds south of Region IVincreased the catch levels above those previously obtained; and (3) from 1984 to 1986 a reorganisationof the fishing fleet occurred due to the opening of the fishery for the red squat lobster(Pleuroncodes monodon) along with an increase in world prices for this resource. Between 1989and 1991 the fishery was closed in Regions V and VIII, but it remained open in northern Chile. Inthis northern area after 1986 there was an increase in landings of squat lobster reaching 10,620 tin 1995. After this year there was a clear decrease in these landings, reaching 4000 t in 2000.Since 1995, the three species are subject to catch quotas per boat owner, based on a totalallowable catch (TAC), which is determined annually, following direct resource evaluations. Aperiod of difficulty in the crustacean fisheries due to decreasing stocks began in 1999 in northerncentralChile (SUBPESCA 2005a,b). The TAC per Fisheries Unit of nylon shrimp (Regions II–VIII)dropped over four subsequent years from 10,000 t in 1997 to only 4000 t in 2000 (i.e., a 60%decline). The TAC of the fishery for the yellow squat lobster in Regions III and IV dropped from6000 t in 1998 to 4000 t in 2000, representing a reduction of 33% during that time period. Thissubstantial reduction in landings caused a major decline in the activities of the fishing fleet and thepacking plants. During 2002, some companies closed, with important losses in employmentproducing socioeconomic impacts in the regions affected (Pérez 2003, 2005). This brief overview284
THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILEunderscores that the fishery of these benthic crustaceans is highly dynamic, driven not only bybiological factors, but also by administrative decisions and economic considerations. In the followingsection some relevant information on the biology of these three species is provided beforepresenting a case study highlighting the relationship between catch-based stock estimates andspecies biology.Basic biology of nylon shrimp and squat lobstersThe main bathymetric distribution of these species shows a strong overlap with the OMZ between~50 and ~600 m, where they occur on gravel and mud bottoms (SUBPESCA 1999a,b). Theirlatitudinal distribution ranges from 25°S to 39°S (Heterocarpus reedi), from 6°S to 40°S (Pleuroncodesmonodon), and from 29°S to 38°S (Cervimunida johni) (Acuña et al. 1997, 1998, Quirozet al. 2005). Little is known about their food resources. All three species themselves are importantprey organisms for demersal fish predators (e.g., flounders and hake), and it has been discussedthat the OMZ may represent a refuge from predation (Villarroel et al. 2001). Most informationabout the biology of these crustacean species is based on analysis of specimens obtained fromcommercial or research catches.Heterocarpus reediAvailable data suggest seasonal migrations with the main concentrations of shrimp found at greatdepths (>400 m) in austral summer, at shallow depths during austral winter (20,000 embryos. Males reach substantially greater sizes and weights than females, and averagesize at first maturity (of females) varies substantially among years (Acuña et al. 2005). It is generallyassumed that each female produces only one clutch per year, and Arancibia et al. (2005) suggestedthat C. johni is a slow-growing species, with individuals living up to 11 yr.Pleuroncodes monodonBased on the main occurrence of ovigerous females it has been suggested that mating occurs mainlyin late summer/early autumn (Palma & Arana 1997). Embryo incubation extends from April toNovember, with the highest proportion of ovigerous females observed in July–August (Palma &Arana 1997). All embryonic developmental stages were found between June and October (Palma& Arana 1997), suggesting that not all females mate at the same time. The first planktonic larvae285
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