Use of radiotelemetry to track threatened dorados Salminus brasiliensis in the upper Uruguay River, Brazil

摘要

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).