Changes In The Hydrological Regime Of Coastal Lagoons Affect Mangroves And Small Scale Fisheries: The Case Of The Mangrove-Estuarine Complex Of Marismas Nacionales (Pacific Coast Of Mexico)

The estuarine system of Marismas Nacionales (Pacific coast of Mexico) is a Biosphere Reserve that is considered to be the most extensive mangrove region in the American Pacific, and an important region for artisanal fisheries since prehispanic times. Significant hydrological changes occurred in this region after 1976 when an artificial channel was constructed to connect the sea to the main body of the estuary. The channel was originally build to be 40 m wide by 2 m deep, but erosion of the sand barrier (consequence of strong ebb currents) caused the formation of a channel that is presently more than 700 m wide and 20 m deep. The consequent hydrological shift caused the mortality of more than 15,000 ha of mangroves; more than 33 % of the mangroves were affected by 1999, and it is considered that the process of deterioration is still happening. On the other hand the opening of the artificial channel improved the shrimp and finfish fisheries in the region: the number of fishing communities increased, as did the shrimp and fish landings, and large populations of pershell (Atrina maura) settled in the region. Several publications state the importance of mangrove as a key habitat for sustainable fisheries, but environmental conditions in some mangrove areas can be extremely difficult for the survival of fishes, crustaceans and mollusks (i. e. due to oxygen depletion). Thus, it seems that the role of mangroves is more related to the support of fisheries in surrounding habitats such as tidal channels, intertidal sand banks, seasonal flood plains, coastal lagoons and adjacent marine areas than "in situ" mangroves. This chapter describes the mangrove deterioration process in the region and proposes the hypothesis that mangroves combined with freshwater inputs, tidal channels and coastal lagoons with tidal influence and seasonal floodplains are required for a mangrove forest to be considered an adequate fish habitat, and therefore an important fishing region. Riverine, fringe and overwash mangrove forests are more beneficial to fisheries than basin and dwarf mangroves that play different ecological functions other than supporting fisheries.