ECOLOGY OF THE COPORO, PROCHILODUS-MARIAE (CHARACIFORMES, PROCHILODONTIDAE), AND STATUS OF ANNUAL MIGRATIONS IN WESTERN VENEZUELA

Deforestation, overfishing, pollution, and construction of dams have s everely impacted migratory fishes of western Venezuela. The coporo, Pr ochilodus mariae (Prochilodontidae), has supported the largest commerc ial fishery among the species that have seasonal long-distance migrati ons between rivers of the Andean piedmont and the llanos floodplains. During the period July 1988 to November 1990, coporo ecology was studi ed in the Rio Bocono and the Bocono-Tucupido reservoir in estado Portu guesa. Coporo females mature at age 2 at 23 cm SL. Relatively few copo ros were captured from the reservoir and the R. Bocono upstream. No co poros were encountered in the river > 3 km upstream from the reservoir nor in hypoxic regions of the reservoir > 4 m deep. In the river segm ent immediately downstream (0-4 km) from the Bocono Dam, the stock was comprised of mostly juveniles (78% < 17 cm SL), and this size/age str ucture was relatively stable over time. In recent years, overfishing d ownstream from the dam has reduced the densities and sizes of coporos in the R. Bocono. The river segment 4-16 km below the dam was comprise d of 78% adults. Few coporos > 3 yr and > 30 cm SL were found in the r ivers, whereas none were < 4 yr and < 30 cm in the reservoir. Detritus was consumed more than algae by coporos in the reservoir and by adult s relative to juveniles among river-dwelling fish. In both reservoir a nd river fish, gonadal development was initiated during late November and peaked during May-June. We found no evidence of successful reprodu ction in the reservoir, and mature adults in the lower river segment d isappeared during June, presumably having migrated to the floodplains of the low llanos for spawning. From mid-November 1989 until March 199 0, coporo 'ribazons' (schools of ascending migrants) of diminishing de nsities were surveyed from the R. Apure upstream to the R. Bocono. 'Ri bazons' have been eliminated or greatly diminished in nearly 80% of th e principal rivers of the Andean piedmont in western Venezuela. Manage ment options to assist this economically and ecologically important sp ecies are discussed.