Anthropogenic disturbances of fish populations of the llanos and the Andean Piedmont of Venezuela Perturbaciones causadas por el hombre a las poblaciones de peces de los llanos y del piedemonte andino de Venezuela
Winemiller, K.; Marrero, C.; Taphorn, D.
BioLlania 12: 13-48
For most of the species of fishes that live in the low llanos of Venezuela, the habitat that they occupy is not a closed system. On the contrary, from a biological point of view, their habitats are intimately connected to the waterways of the Andean piedmont, and together form one large aquatic ecosystem. The continuity between these two regions exists because the majority of the commercially important species migrate from the lowlands upstream to the small rivers of the piedmont to take refuge there, during the dry season, and later return to the productive flood plain were they reproduce during onset of the rainy season, in april or may. However the ancient connection has been recently broken by the activities of man due to several processes: a) widespread deforestation; b) an increase in the point and not-point sources of water pollutants; c) the construction of dams; and d) over fishing. Satellite image studies have shown that Venezuela is one of the South American countries to have suffered the greatest losses of forest, and that the rate of loss has accelerated greatly in the last few years. This process, by drastically reducing the amount of water in the rivers during the dry season, directly affects the migratory cycle of many fishes. Furthermore, the reduced flow concentrates the toxic effects of agricultural and other pollutans, and allows fishermen to exploit regions of the rivers that were hitherto too deep effective fishing. The principal negative impact of point source pollutans in these rivers has yet to be fully appreciated. This is an important point to emphasize, because of the migratory nature of most commercial fish species, an apparently small, local mortality could affect the few adults that reach sexual maturity and so have far reaching consequences by eliminating the founders of the next generation of fishes that would inhabit the entire watershed. Thus the loss of just a few reproductive fishes can have a negative impact many orders of magnitude beyond the number of fishes that are directly killed by the contaminant. In addition to these perturbations, hydroelectric dams and fishermen's nets form barriers along the tradition routes offish migrations. For example, the Dorado, Salminus hilarii, that was once an abundant fish of the Andean piedmont, and highly appreciated by sport fisherman's region is now in danger of extintion in Venezuela.