Migration and spawning of female surubim (Pseudoplatystoma corruscans, Pimelodidae) in the Sao Francisco river, Brazil

Surubim, Pseudoplatystoma corruscans, is the most valuable commercial and recreational fish in the Sao Francisco River, but little is known about adult migration and spawning. Movements of 24 females (9.5-29.0 kg), which were radio-tagged just downstream of Tres Marias Dam (TMD) at river kilometer 2,109 and at Pirapora Rapids (PR) 129 km downstream of TMD, suggest the following conceptual model of adult female migration and spawning. The tagged surubims used only 274 km of the main stem downstream of TMD and two tributaries, the Velhas and Abaete rivers. Migration style was dualistic with non-migratory (resident) and migratory fish. Pre-spawning females swam at ground speeds of up to 31 km day(-1) in late September-December to pre-spawning staging sites located 0-11 km from the spawning ground. In the spawning season (November-March), pre-spawning females migrated back and forth from nearby pre-spawning staging sites to PR for short visits to spawn, mostly during floods. Multiple visits to the spawning site suggest surubim is a multiple spawner. Most post-spawning surubims left the spawning ground to forage elsewhere, but some stayed at the spawning site until the next spawning season. Post-spawning migrants swam up or downstream at ground speeds up to 29 km day(-1) during January-March. Construction of proposed dams in the main stem and tributaries downstream of TMD will greatly reduce surubim abundance by blocking migrations and changing the river into reservoirs that eliminate riverine spawning and non-spawning habitats, and possibly, cause extirpation of populations.