O efeito da estocagem de juvenis na abundância do tambaqui (Colossoma macropomum Cuvier, 1818) em lagos de várzea na Amazônia Central

Abstract

Tambaqui is one of the most known and appreciated fish. Its flesh attain high value in regional economy, therefore it is an important product of the floodplain. There are strong indications that natural population is depressed due to over fishing. Stock enhancement can be used to mitigate depletion of natural populations and to increase production. The objective of this work was to test the viability of stock enhancement of tambaqui juveniles in floodplain lakes in Central Amazon. In 2000 and 2001 five lakes were treated by adding 1000 and 1500 juveniles tambaqui/ha (5cm). The effect of stocking was inferred by variation in abundance of tambaqui. The population density six months after stocking was estimate trough marking and recaptures method (Schumacher-Eschemeyer). Economic viability of the stock enhancement was evaluated by cost-benefit relationship. Main predators of juvenile tambaqui were identified and the existence of an ecological interrelation explaining the variation of abundance of tambaqui in the floodplain lakes was examinated. Findings evidenced strong oscillation of the catch per unit effort (CPUE) in experimental lakes, however no significant difference was detected between abundance of treated and control lakes. It was evidenced an increase of the CPUE in years of stocking and a decrease in the year without treatment. The possibility of this behavior is very low (0.1%). The adjusted of recapture rates of stocked fish varied, between 1.35% (lake Jacaretinga) and 2.15% (lake Cavalo). Tambaqui densities were low, 6 and 15 ind/ha in the lake Jacaretinga (2000 and 2001) and 32 ind/ha in the lake Cavalo (2001). Gut content of 80 individual predators were analyzed evidencing that 20% of them had consumed tambaqui juvenile. Serrasalmus rhombeus, Pygocentrus nattereri and Acestrorhynchus falcirostris were the main predators. Variation in tambaqui abundance was not explained by variation of competitors, predators or lake area. We concluded that stock enhancement is a viable alternative, as extensive aquaculture, and can increase tambaqui abundance in some lakes, however it is not clear if this management strategy effectively increases the tambaqui production in the Amazon basin.