Abundância de juvenis do ano de Characiformes migradores em áreas de várzea do baixo rio Solimões (Amazonas, Brasil)

Abstract

In the central Amazon there are four species of migratory Characiformes under pressure from commercial fishing, the tambaqui (Colossoma macropomum), the matrinxã (Brycon amazonicus) and the two jaraquis (Semaprochilodus spp.). Records of landings in Manaus and abundance of larvae data in the lower Solimões river indicate equilibirum in some of these stocks and overfishing for others. To improve measures of analysis of fisheries, variables related to the young fish have been used in order to obtain estimates of fishing recruitment. This study aimed to estimate the abundance of young-of-year of these species in two stretches of the lower Solimões river, one near Manaus and another one detached about 500 km from the city, considering the temporal variation of the experimental period. From 12/2007 to 05/2008 were taken monthly 20 sampling points in each area, including points above and below the confluence with tributaries of black or clear waters with the Solimões river (white water). Samples were collected in different habitats in the floodplain of the lower Solimões. Analysis of covariance was applied to test differences between mean abundance, taking into account the variation of the water level in Negro river as a covariate. Multiple regressions were used to check the influence of local environmental factors on the abundance of young-of-year. Despite the large number of individuals of B. amazonicus captured in two sections sampled, the area near Manaus showed significantly lower abundance of young-of-year of the species, the covariate significantly related to the abundance of juvenile. Gender Semaprochilodus did not show differences in the abundance of young-of-year between areas. Were caught only 28 young-of-year of C. macropomum adding the two areas. The multiple regression analysis for the effects of habitat on the abundance of juveniles was not applied to C. macropomum due the low number of individuals captured. The young-of-year abundance of B. amazonicus seems to be related to equilibrated stocks of this species in the Solimões river above the meeting of the waters, in contrast to stocks occurring in the lower Negro river which may have lower values of biomass recruited to the fishery. Gender Semaprochilodus spp. showed more homogeneous between the two sites studied, which can demonstrate that the fishery of jaraquis in Manaus region is sustained largely by the strong adaptation of these species to black water systems in the Amazon basin. C. macropomum is a species historically under heavy fishing pressure, which currently presents the characteristics of recruitment overfishing in the lower Solimões. Suggested measures for fisheries management of the tambaqui is presented, taking into account the amazonian reality and the importance of this resource for commercial and artisanal fishery in the Central Amazon.