The role of semi-emclosed embayments for the metapopulation dynamics of coastal marine invertebrates in the Humboldt Current System
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|Other Titles:||Die Rolle halbgeschlossener Meeresbuchten für die Metapopulationsdynamik mariner Invertebraten im Humboldt Auftriebssystem||Authors:||Olivares, Gonzalo||Supervisor:||Wolff, Matthias||1. Expert:||Lemke, Peter||2. Expert:||Schlitzer, Reiner||Abstract:||
During 1980s and 1990s, the resources on which the Chilean artisanal fishery is based suffered a severe crisis. Since the crisis was driven principally by the lack of compliance with the central fishery agency, a new fisheries act introduced in 1991 the Management and Exploitation Areas (MEA), a form of co-management based on territorial use rights. This law restricts the co-management to one-by-one arrangements between a particular community and the fisheries authority, which results in the lack of any formal strategy for coordinating managements above the spatial scale of the individual fishers community. Since many important resources for the artisanal fishery form metapopulations, MEAs of different populations could rely on larval transport from other MEAs or fishing grounds outside of their control, making the coordination of managements at each community unavoidable. However, the connectivities among local populations needed to implement this coordination are still unknown for the Chilean coast. Moreover, as connectivity is an emergent property of the natural-human system, what is really needed is a system that delivers information about the metapopulation to co-management institutions and that is sensitive to actions derived from co-management negotiations. The aim of the present study was to develop a preliminary tool for this information system based on available information. Three major factors influencing connectivity were studied: 1) the coastal circulation, 2) the size and location of patches in which the adult individuals are distributed, and 3) the size of stocks at each management unit. Ancillary time series of satellite sea surface temperature were used to track thermal features in successive days, obtaining some spatial patterns of currents. These patterns were summarized in simple rules that, applied to a realistic geometry of the coast, were utilized to generate idealized circulation fields. These fields were used to force the larvae movement in a simple Lagrangean scheme. Literature records were combined with geographic information to delimitate location and size of suitable patches for local populations. The resulting larval transport was included into a matrix model of the metapopulation dynamics. Simulations with the model were used to inform the discussion about the proposal of transforming the entire coast of central Chile in MEAs. The results confirm the reported daily variability in the coastal circulation associated to changes in the alongshore wind. Furthermore, besides offshore dynamics associated to headlands in Lengua de Vaca and Punta Choros, the observed variability close to the coast is principally along the shore, and includes reversion of coastal currents. A single general regime of circulation applied to a realistic coastal geometry will produce a rich variety of larval transport patterns, which cannot be adequately reproduced by a single dispersion function for the whole coast. Current variability associated to coastal trapped waves are much more important for connectivity than those associated to the upwelling. Since the energy of coastal-trapped waves changes during El NiÃ ï¿½Ã ±o events, the NiÃ ï¿½Ã ±o/NiÃ ï¿½Ã ±a cycle will change the connectivities. The way in which this cycle modifies the connectivities will depend on the annual mean of the currents. Based on the available information about alongshore mean current, the two largest local populations are sources of larvae for the others, and are, therefore, the only ones that could be set aside as MEA under the present co-management system. This also shows that under the current fisheries act both, the TAC and the co-management systems are compatible provided that the source/sink structure is known. Given the dependence of populations from imported larvae, the transformation of the entire coast of the IV region in MEAs requires the modification of the present co-management institutions to promote the coordination of management among the fishers communities. The system is highly sensitive to management options, being the effects of local changes in this management difficult to visualize a priori, without simulations such as done in this study.
|Keywords:||Metapopulation, Connectivity, Chile, Mesodesma donacium||Issue Date:||21-Oct-2005||URN:||urn:nbn:de:gbv:46-diss000100364||Institution:||Universität Bremen||Faculty:||FB2 Biologie/Chemie|
|Appears in Collections:||Dissertationen|
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