the humboldt current system of northern and central chile - figema

More documents

Recommendations

Info

MARTIN THIEL ET AL.& Fernández 1998, González et al. 2006), albeit it appears to be deficient in particular situations(e.g., Gelcich et al. 2006).Since resource stocks are continuously monitored in management areas, with captures wellcontrolled and registered, it has been possible to begin to understand the underlying nature offluctuating landings. Contrary to the above-described classical pattern of a badly managed fishery,it has often turned out to reflect the natural variability of the environment of the HCS. Global-scalephenomena, such as EN events, which produce an outburst of some resources and disappearanceof others, together with more localised processes of upwelling and current systems, generate acomplex, spatially and temporally changing, mosaic of conditions. Fluctuating fisheries are mainlythe consequence of this, the fishermen following (and suffering) natural variations, but not alwayscausing them, as generally assumed. The following description of the four most valuable resourcesfished by artisanal fishermen illustrate this.Scallop fisheryCase studiesThe scallop fishery can be considered as a ‘boom-and-bust’ fishery, where the ‘boom’ is causedmainly by EN events (Wolff 1987, Stotz 2000, Wolff & Mendo 2000, Stotz & Mendo 2001, vonBrand et al. 2006). During EN, recruitment of Argopecten purpuratus is intense, and duringfollowing years, given the normal fast growth of the species (Stotz & González 1997), huge stocksof scallops build up, with fluctuations of several orders of magnitude between years (Figure 22A,stock increased with EN 1982–1983; Figure 23A stock increased with EN 1997–1998) (Stotz &Mendo 2001). However, following the increased scallop stocks, the development of similar predatorpopulations and/or the shift of prey preference of predators in response to increased scallopabundance (Ortiz et al. 2003), together with the fishery, leads to an increasing mortality, whichfinally generates the ‘bust’ (Figure 23A) (Wolff 1987, Jesse & Stotz 2002, León & Stotz 2004).Fishermen are just able to take advantage of part of the EN production before the natural mortality,caused mainly by predation (e.g., by Octopus mimus), but also by mass strandings (González et al.2001), takes most of the scallops away (Figure 23B). Normal (LN) years are characterised by smalland, due to spatially (Aguilar & Stotz 2000) and temporally variable recruitment, fluctuating scallopstocks, which supply a low-level fishery (Figure 22A). Taking advantage mainly of natural recruitmentwhile preventing predation, in northern Chile aquaculture has been able to build up stocksand harvest at levels several times above fishery production (Figure 22A) (Stotz 2000).Surf clam fisheryThe ‘macha’ Mesodesma donacium fishery also shows boom and bust fisheries along the coast(Figure 22B). In the past, on most sites a relatively stable low-level fishery existed, produced byfishermen working in the intertidal zone. During the mid-1970s fishermen learned also to dive forthis resource, which means putting the boat behind the breakers (‘rompiente’), diving, loaded withat least 40–50 kg of lead, through the surge and then working underneath the breakers. This beganin Region V (32–35°S). After having depleted the local stocks in Region V, some fishermen cameover to Region IV (29–32°S), where the local fishermen quickly learned the same technique. Thishas generated a tradition of divers, mainly from Regions IV and V, working on the macha alongthe entire Chilean coast, making use of and depleting macha stocks throughout the country (Figure22A). However, after the establishment of AMERBs for this resource, other reasons for the depletionbecame apparent. With the EN 1997–1998 all the macha beds between Arica and Coquimbo,managed conservatively within AMERBs, died off within a few days. The beds in Coquimbo weresmothered by mud, washed into the bay by a river flood due to heavy rainfall (Miranda 2001). For280
THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILEStock density (ind m −2 )20151050El Niño92 93 94 95 96Harvest +Predators +StrandingA97 98 99 00 01 02 03 04Stock (million ind)121086420AugOct< 90 mmDecFeb> 90 mm HarvestAprJunAugOctDecB20002001Stock (t)6005004003002001000AprJun< 60 mm > 60 mm HarvestAugOctDecFebFigure 23 (A) Stock size of the scallop Argopecten purpuratus in an AMERB, (B) the impact of the harveston the decrease of the same scallop stock, and (C) of a Mesodesma donacium stock in another AMERB, ‘Areade Manejo y Explotación de Recursos Bentónicos’ (MEABR, Management and Exploitation Area for BenthicResources).AprJunAugOctDecFebApr1999 2000 2001CJunArica no specific reason was identified, but increased temperatures have been mentioned as a causeof mortality for the same species in Peru (Arntz et al. 1987, 1988). In the Coquimbo area, the onlybeds left were in Tongoy Bay, which were exploited according to what was considered then a veryconservative strategy. However, despite dynamic (and apparently conservative) management, thesebeds also disappeared (Figure 23C) (Aburto & Stotz 2003). Captures were almost irrelevantcompared with the natural decrease (Figure 23C), which was not renewed by recruitment, becauselarval supply is spatially (Ortiz & Stotz 1996) and temporally very irregular or absent during manyyears. A similar situation was shown for macha beds managed within management areas in RegionVIII, where, due to the almost complete lack of recruitment, the stocks within the AMERBscollapsed by 2004 (Figure 22B) (Stotz et al. 2004). Following their disappearance during or after281
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: THE HUMBOLDT CURRENT SYSTEM OF NORT
Page 85: THE HUMBOLDT CURRENT SYSTEM OF NORT
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
show all

the humboldt current system of northern and central chile - figema

Create successful ePaper yourself

Delete template?

Save as template?