Patagonian Shelf large marine ecosystem
The Patagonian Shelf Large Marine Ecosystem (LME) extends from Uruguay to the Strait of Magellan. It has a total area of about 2.7 million square kilometers. The continental shelf is relatively narrow in the north but widens progressively to the south, where it reaches a width of about 850 kilometers (km). The LME has a distinctive bathymetry and hydrography. It is influenced by two major wind-driven currents: the northward flowing Falklands/Malvinas Current and the southward flowing Brazil Current (Bakun, 1993). The two currents provide the LME with a distinctive ecological boundary to the east. The LME is a composite area with a unique combination of characteristics.
The Patagonian Shelf LME is considered a Class I, highly productive (>300 gC/m2-yr) ecosystem based on SeaWiFS global primary production estimates. While the southward flowing Brazil Current is warm and saline, the northward flowing Falklands/Malvinas Current carries cool, less saline, nutrient-rich sub-antarctic water towards the equator. The two currents mix their waters at a Confluence Zone (CZ). The CZ is a wide area characterized by intense horizontal and vertical mixing. It is situated on average at the approximate latitude of 39 degrees south, but is displaced to the north in the winter. The exchange of water masses of different temperatures and salinity affects biological productivity. The characteristics and dynamics of the CZ, however, are still poorly understood. There are significant coastal tidal fronts in this LME that divide the coastal domain from the outer shelf domain. A comprehensive study of productivity has not been conducted for this LME, although there are productivity figures available. Frontal zones are areas of high productivity. There is high phytoplankton production at the 220 km wide mouth of the Rio de la Plata, a river discharging large quantities of freshwater and sediments into the LME. There are commercially important fisheries in that area. Phytoplankton species are dominated by dinoflagellates, coccolithophorids, and cyanophyceans. There are few diatoms. Zooplankton composition shows a high abundance of Calanoid Copepoda, Chaetognatha, Salpidae and Hydromedusae. The coastal waters of the sub-tropical Brazil Current are areas of lesser productivity. The ecosystem provides a favorable reproductive habitat for anchovies and sardines, when physical processes such as upwelling and mixing combine favorably in special configurations (Bakun, 1993), so that fish larvae remain close to food sources. There are favorable reproductive habitats for small, pelagic-spawning clupeoids (Bakun and Parrish, 1991). The LME supports significant seabird and marine mammal populations (Bakun, 1993).
Fish and Fisheries
The LME is rich in a variety of fishery resources, including hake (Common hake and Patagonian hake), anchovy, squid, southern blue whiting, red shrimp, and sardines. The total catch, which was 1 million tons in the mid 1970s, increased to 2 million tons by 1987. Hake and anchovy, which are normally to be found in two separate zoogeographic provinces, coexist in this LME. Common hake is abundant in the northern shelf and off of Uruguay and southern Brazil. Hake is a major fisheries export for Argentina. Uruguay has developed a smaller hake fishery off the Rio de la Plata. The Atlantic anchovy is a key species in the trophic system (Bakun, 1993). It is central to the diet of primary and secondary carnivorous species of significant economic importance such as hake and squid. Only Argentina targets the Atlantic anchovy (Engraulis anchoita), and it is presently underexploited. It inhabits an extended stretch of coastal habitat from Cabo Tres Puntas in south-central Argentina to Cabo Frio in Southern Brazil. It spawns in the southeastern Brazilian Bight from late winter to early summer, and is a temperate rather than a tropical species, occurring at depth or in upwelling plumes (Bakun, 1993). The squid fishery became prominent in the 1980s, with catches by both Argentina and Uruguay off the Rio de la Plata. In 1987 the Food and Agriculture Organization (FAO) Fisheries Department issued a report indicating that squid stocks were being maximally exploited and probably overfished (Csirke, 1987). There was a peak in 1989, followed by a decline in 1990. On the other hand, the southern blue whiting is not fully utilized. The Argentine red shrimp is the highest valued fishing product exported by Argentina. Like the anchovy, the sardine (genus Sardinops or Sardinella) is a key link in the local trophic system (Bakun, 1993). A global sardine/anchovy recruitment project (SARP) was initiated in 1983. Its goal was to study recruitment variability and the reproductive biology of both these species. Global climate change could intensify coastal winds, disrupting the conditions provided by upwelling, sheltered areas, and mixing that are so favorable to the anchovy and sardine fisheries ( Bakun, 1993). The University of British Columbia Fisheries Center has detailed catch statistics for this LME.
Pollution and Ecosystem Health
Some pollution issues stem from the presence of the two major metropolitan areas (Buenos Aires and Montevideo) situated along the Patagonian coast. These are also areas of industrialization and resource exploitation. Threats facing the Patagonian shore are untreated sewage, oil pollution, and industrial and municipal pollution loading. Out of Buenos Aires, effluents from tanneries, dairy and paper industries, chemical and pharmaceutical plants and oil refineries pollute the coastal waters. These anthropogenic disturbances, the degradation in water quality, have an impact on living marine resources and contribute to eutrophication and loss of habitat. The Rio de la Plata, a river with a 220 km wide mouth, discharges freshwater, sediments and pollutants into the LME.
In terms of fisheries, Argentina shifted from hake to species such as squid following the Falklands conflict (1982). Uruguay and Argentina have an artisanal fishery of croakers and weakfishes. Other marine-related economic activities include tourism (Uruguay) and offshore oil exploration (Argentina). Buenos Aires is one of the world’s major seaports and is the center of many of the country’s industrial activities. Many of Argentina’s exports and imports are transported by rivers and through ocean shipping.
Argentina and Uruguay are the two countries bordering this LME. Consensus in the management of the LME is an elusive goal because of differing jurisdictions and a different acceptance of international customary law and conventional law. The two countries both have 200-mile zones. An area held in common by both Argentina and Uruguay is the Rio de la Plata. A treaty for the exploitation of shared living resources in the estuary was signed and entered into force in 1974. An Argentine-Uruguayan Technical Commission for the Rio de la Plata Maritime Front has jointly managed the shared hake stock since 1975. In 1991, a Common Market was established by Argentina, Uruguay, Brazil and Paraguay (MERCOSUR), to create a zone of free trade. The 1982 Falklands conflict between Argentina and Great Britain had an effect on governance and fisheries management around the Falklands/Malvinas Islands. The Falklands Inner Conservation Zone (FICZ) was established in 1986 by the British for the administration of fisheries, but was strongly contested by Argentina. In 1990, a joint Falklands Outer Conservation Zone (FOCZ) was established with a view to rebuilding depleted fish stocks.
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