Physical Setting and Study Area

San Blas is located at the southern extremity of the Teacapán - Agua Brava - National Wetlands complex on the Pacific coast of Mexico in the States of Sinaloa and Nayarit. The map below illustrates the location of this complex.

The region delineated on the map includes land areas below ten meters altitude in which the entire complex is found. This wetland ecosystem is bounded by 22º 04´and 22º 35´ north latitude, 105º 20´ and 105º 50´ west longitude. It covers an area of 852 square kilometers and has about 150,000 hectares of wetlands, flood plains, lakes and mangroves. The rivers Cañas, Acaponeta, Rosa Morada, Bejuco, San Pedro y Santiago drain into the complex.(Flores Verdugo et al, 1992). The map below shows the areal extent of these rivers.

These rivers drain approximately 150,000 square kilometers or very nearly 20% of the entire land area of the Mexican Republic. The entire wetland complex is formed by the deposition of alluvial materials carried down to the mouths of these rivers.

The wetland complex includes alluvial plains; coastal lagoons and estuaries; swamps; old, sandy beach ridges; and nearly parallel, linear lagoons. The predominant vegetation consists approximately 113,248 hectares of mangrove. The map below shows the distribution of mangrove in the wetland complex.

The mangrove species found in the region are: mangle rojo (Rhizophora mangle), mangle negro (Avicenna germinaus), mangle blanco (Laguncularia racemosa) and botoncillo (Cornocarpus erectus linnaeus). This region shelters important populations of jaguars, crocodiles and is the winter refuge of many different migratory birds. It also provides critical habitat for a large variety of fishes, crustacea, and molluscs of economic importance to Mexico. Without doubt, this wetland complex is one of the most important mangrove ecosystems on the Pacific coast of the Americas, matched in size only by the wetlands on the Chiapas coastline in southern Mexico. [note]

Although the health of the entire wetland complex is an important issue, our resources were insufficient to undertake such a large task. We decided to initiate our effort in the immediate area around San Blas, using the political boundaries of the Municipality of San Blas to define the study's scope. The map below shows the location of the study area.

The area of interest includes all of the territory in the municipality with an elevation of less than ten meters. The selected region has an area of 358 square kilometers, of which 135 square kilometers was identified as mangrove on the Instituto Nacional de Estadisticas, Geografia, e Informatica (INEGI) 1:50,000 topographic map sheets compiled from photogrametric data collected between 1968 and 1972 . This figure represent approximately 12% of the mangroves in the entire wetland complex, which, on the topographic maps, have an area of 1,117 square kilometers.

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