the humboldt current system of northern and central chile - figema

More documents

Recommendations

Info

MARTIN THIEL ET AL.length of fishery unit, Law 19.173). This action was set to last until 2002, but was later extendeduntil 2012 (Law 19.849). Finally, in 2004 a similar management tool was established for the artisanalfleet, the Regimen Artesanal de Extracción (RAE, Artisanal Capture Regime), which in this caseassigns the artisanal fraction of the Annual Global Quota to one or more artisanal fishermen’sorganisations in each fishery unit, which in turn divide it between members.As becomes evident from the preceding paragraphs the currently valid management rules (fullexploitation, Global Annual Quota, LMCA, etc.) have been implemented when landings started todecrease or stocks had already dramatically declined. Therefore, fisheries of small pelagic fisheriesin the HCS off Chile are presently managed at much lower population levels than they used to bein previous decades. In fact, stocks of anchovy and common sardine in central Chile are consideredto be overfished (Cubillos et al. 2002). The interaction between administrative effects on landingsand fishery-induced impacts on stocks complicate the detection of direct relationships betweenenvironmental factors and fish stocks. In addition to fishery-independent stock surveys, studies ofthe basic biology of individual species, of biological interactions (predators, competitors, food),and of the role of climatic and coastal oceanography are required in order to improve our understandingof the factors driving the population dynamics and distribution in northern-central Chile.AquacultureAccording to the latest reports published by the Food and Agriculture Organization of the UnitedNations (FAO 2006), the contribution of aquaculture to the world supply of fish and shellfish“continues to grow faster than any other productive sector of animal food origin”. The worldproduction of aquaculture registered in 2002 rose to 51.4 million t (including aquatic plants), withAsian countries producing 91.2% of this. In 2002, Chile contributed only 1.4% of the world’s totalproduction, but it is among the 10 countries showing the fastest growth in aquaculture production.Fisheries and aquaculture are for Chile one of the most important economic activities with a totalincome of U.S. $2,246 million in 2003, of which aquaculture contributed U.S. $1600 million. Thelargest share of the Chilean aquaculture production (80%) is from southern Chile (41–46°S), withsalmon and mussels and to a lesser extent oysters, seaweeds and more recently red abalones (Haliotisrufescens) being the most important resources (FAO 2006).Aquaculture activities along the coast of northern-central Chile (18–35°S), although not reachingthe same levels as in southern Chile, have been continuously growing during the past twodecades (FAO 2006). Given that the shorelines of northern-central Chile are relatively exposed towave action and fully subjected to the effects of ENSO, it is particularly important to take thesefactors and interannual variability in oceanographic conditions into account. In fact, all aquaculturecentres in northern and central Chile are located in relatively sheltered bays. The main naturalresources cultured in northern-central Chile are scallops (Argopecten purpuratus) and seaweeds(Gracilaria chilensis), and their natural populations are also exposed to strong seasonal and interannualvariations. Small-scale culture of some other species (bivalves Mesodesma donacium andTagelus dombeii, gastropods Concholepas concholepas and Fissurella spp., sea urchins Loxechinusalbus) has also been attempted but has not reached a commercial stage, mainly due to biological(long larval periods) and logistic (food supply) reasons. Several introduced species are also culturedin northern Chile, namely the Pacific oyster (Crassostrea gigas), which has been cultured on asmall scale since 1970, and during recent years increasingly abalones (Haliotis rufescens andH. discus hannai).The main resource cultured during the past two decades in northern Chile is the scallopArgopecten purpuratus. Culture centres are located in bays, namely Isla Santa Maria and BahíaMejillones (22°S), Bahías Caldera, Calderilla and Inglesa (27°S), and Bahías Guanaqueros andTongoy (30°S). Standing stocks and productivity in these bays are below those of similar bays in292
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
Page 1 and 2:
Oceanography and Marine Biology: An
Page 3 and 4:
THE HUMBOLDT CURRENT SYSTEM OF NORT
Page 5 and 6:
Page 7 and 8:
Page 9 and 10:
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48: THE HUMBOLDT CURRENT SYSTEM OF NORT
Page 97: THE HUMBOLDT CURRENT SYSTEM OF NORT
Page 149 and 150:
show all

the humboldt current system of northern and central chile - figema

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?