Little is known about the seasonal movements of fish that inhabit large rivers in South America, which makes it difficult to identify potential threats to fish populations associated with the proliferation of hydropower developments. Dorados Salminus brasiliensis (Characiformes) are large riverine piscivores that are targeted by recreational and commercial fishers and are considered regionally 'vulnerable' in Brazil due to overfishing, pollution, and habitat fragmentation. Here, we used radio telemetry to study the seasonal movements of dorados in the upper Uruguay River, Brazil, to provide the first information on large-scale migratory biology and to inform management and conservation actions. From November 2001 to July 2003, 73 dorados were radio-tracked using aerial surveys and 7 fixed radio telemetry stations installed in a section of the upper Uruguay River covering ~400 km. Despite use of an extensive radio telemetry array and aerial tracking, nearly 40% of fish tagged at the downstream site were never detected, suggesting unreported harvest, post-release mortality, or migration to tributaries or downstream reaches that extended beyond the tracking area, emphasizing the challenges of working in such a large study system in jurisdictions where research capacity and funding are limited. Nonetheless, this study yielded the first data on the migratory biology of dorados and revealed that a segment of the population is quite mobile and thus could be negatively impacted by river fragmentation, suggesting the need for management strategies that maintain connectivity (e.g. fish passage facilities).
A preliminary study on the application of radio-telemetry techniques to describe the movements of fish in a bypass channel at Itaipu Dam (Paraná River), known as "Canal da Piracema," was carried out between January and February of 2004. Fourteen individuals of six species (Prochilodus lineatus, Leporinus friderici, Schizodon borellii, Pseudoplatystoma fasciatum, Pterodoras granulosus and Cichla kelberi) were intragastrically and surgically radiotagged and monitored by three experimental fixed radio-telemetry stations installed in the upper portion of the Canal. The surgical implantation of transmitters and the anesthesia using clove oil proved to be more efficient and allowed easier handling in comparison to intragastric implantation and electronarcosis immobilization. The use of fixed stations to obtain data was found to be very suitable for tracking movements of several different fish species in the Itaipu lateral channel. Three species (P. granulosus, S. borellii and C. kelberi) moved downstream after release. Two individuals of P. fasciatum and two of P. lineatus migrated upstream, leaving the channel 7 and 10 days and 2 and 24 days after release, respectively. Leporinus friderici was the only species that did not leave the release site until the end of the study period.Um estudo preliminar sobre a aplicação de técnicas de radiotelemetria para descrever os movimentos de peixes no canal de transposição da UHE Itaipu (Rio Paraná), conhecido como "Canal da Piracema", foi realizado entre janeiro e fevereiro de 2004. Seis espécies (Prochilodus lineatus, Leporinus friderici, Schizodon borellii, Pseudoplatystoma fasciatum, Pterodoras granulosus e Cichla kelberi) totalizando 14 indivíduos foram marcadas com radiotransmissores via cirúrgica e esofágica e rastreados através de três estações fixas experimentais de radiotelemetria instaladas na porção superior do Canal. A implantação de transmissores através de cirurgia e a anestesia por óleo de cravo mostraram-se mais eficientes e de fácil manejo do que a imobilização por eletronarcose e a implantação intragástrica. A utilização de estações fixas para obtenção dos dados mostrouse apropriada para rastrear os movimentos de diferentes espécies no canal de transposição de Itaipu. Três espécies (P. granulosus, S. borellii e C. kelberi) movimentaram-se para jusante após a soltura. Dois indivíduos de P. fasciatum e dois de P. lineatus migraram para montante, deixando o canal 7 e 10 dias e 2 e 24 dias após a soltura, respectivamente. Leporinus friderici foi a única espécie que não deixou o local de soltura até o final do estudo.
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