Ocorrência, biologia e uso das raias de água doce na Baía de Marajó (Pará, Brasil), com ênfase na biologia de Plesiotrygon iwamae (Chondrichthyes : Potamotrygonidae)

Abstract

The present study included stingrays of the Potamotrygonidae family, the only one among elasmobranches that possesses ali representatives exclusively in freshwater. It was carried out in the Islands of Cotijuba and Colares, which are located in the estuarine region of the Marajó Bay, during the rnonths of May, August, October and December of 2000. The sampling included the genera Plesiotrygon, Potamottygon, Paratrygon and a fourth genus that is currently being described. Information related to the frequency of occurrence and biomass indicated the predominance of Potamottygon spp. and Plesiotrygon iwamae in this region. The fishery equipment used selected the size of the stingrays captured. Specific observations were made concerning the feeding and reproductive biology of the species P. iwamae. Stomach content analysis, using the index of relative importance (TRT), indicated that this species feeds mainly on crustaceans and fish. Macroscopic observations of the reproductive organs of males and females were made. The results indicated that this species presents aplacental matrotrophic viviparity with trophonemata. Probably its reproductive cycle is seasonal, is related to salinity changes and several females are captured as they approach the beaches of this bay to reproduce. In this region the freshwater stingrays are routinely captured mainly for food, medicinal and ornamental purposes_ A high number of stingray accidents and treatments were observed in both islands. The conservation of the species of freshwater stingrays requires more knowledge about their biology, follow-ups on their exploration and perhaps management measures.