Migration and Spawning of Radio-Tagged Zulega Prochilodus argenteus in a Dammed Brazilian River

—It is difficult for agencies to evaluate the impacts of the many planned dams on São Francisco River, Brazil, migratory fishes because fish migrations are poorly known. We conducted a study on zulega Prochilodus argenteus, an important commercial and recreational fish in the São Francisco River, to identify migrations and spawning areas and to determine linear home range. During two spawning seasons (2001– 2003), we radio-tagged fish in three main-stem reaches downstream of Três Marias Dam (TMD), located at river kilometer (rkm) 2,109. We tagged 10 fish at Três Marias (TM), which is 5 km downstream of TMD; 12 fish at Pontal, which is 28 km downstream of TMD and which includes the mouth of the Abaeté River; and 10 fish at Cilga, which is 45 km downstream of TMD. Late-stage (ripe) adults tagged in each area during the spawning season remained at or near the tagging site, except for four Cilga fish that went to Pontal and probably spawned. The Pontal area at the Abaeté River mouth was the most important spawning site we found. Prespawning fish moved back and forth between main-stem staging areas upstream of the Abaeté River mouth and Pontal for short visits. These multiple visits were probably needed as ripe fish waited for spawning cues from a flooding Abaeté River. Some fish homed to prespawning staging areas, spawning areas, and nonspawning areas. The migratory style of zulega was dualistic, with resident and migratory fish. Total linear home range was also dualistic, with small (,26-km) and large (53–127-km) ranges. The locations of spawning areas and home ranges suggest that the Pontal group (which includes Cilga fish) is one population that occupies about 110 km. The Pontal population overlaps a short distance with a population located downstream of Cilga. Movements of late-stage TM adults suggest that the TM group is a separate population, possibly with connections to populations upstream of TMD. Fishes of the genus Prochilodus forage on detritus and periphyton and inhabit many South American rivers, where they are an important fisheries resource (Castro and Vari 2003). Zulega Prochilodus argenteus is endemic to the São Francisco River, a large basin southeast of the Amazon River. Zulegas grow to a maximum body weight of 15 kg (Sato et al. 1996) and are one of the most important recreational and commercial fish in the basin (Franco de Camargo and Petrere 2001; Godinho et al. 2003). Despite the importance of zulegas, most aspects of their life history (especially migrations, home range, and spawning locations) are not known. This information is urgently needed to evaluate the environmental impacts of the many large dams and reservoirs planned for the main stem and tributaries. The only available conceptual model of adult Prochilodus spp. migration and total linear home range is from mark–recapture studies on P. lineatus (1⁄4P. scrofa and P. platensis) during the 1950s–1960s (Godoy 1959; Godoy 1962; Bonetto 1963; Bonetto and Pignalberi 1964; Bonetto et al. 1971; Godoy 1975). P. lineatus, which is found in a neighboring basin of the São Francisco River, migrates a maximum round trip distance of 1,300 km between feeding grounds in the main stem and spawning grounds in a tributary (Godoy 1975; Toledo et al. 1986). Spawning occurs during river flooding (Schubart 1954). In the São Francisco River, two mark–recapture studies on zulega provided some information on total linear home range. Fish, presumed to be adults, from different reaches had different total linear home ranges, i.e., 1,100 km maximum displacement for fish tagged in the lower region (Sato and Godinho 2003) and 250 km for fish tagged in the upper region (Paiva and Bastos 1982). Some information on spawning and early life history of zulega is available. During spawning, a female broadcasts hundreds of thousands of small, nonadhe* Corresponding author: [email protected] Received October 8, 2004; accepted January 3, 2006 Published online May 30, 2006 811 Transactions of the American Fisheries Society 135:811–824, 2006 Copyright by the American Fisheries Society 2006 DOI: 10.1577/T04-176.1 [Article]