Fish Use of a Borland-Type Fish Lock in an Iberian River

Abstract

Fish locks were fitted at dams to improve fish migration in Europe, but also in America and Australia. In Iberia, several dams were equipped with locks in the 1970s and 1980s, and in this study the fish use of the Borland fish lock installed in the most downstream dam in the Douro River was investigated by visualizing fish during each cycle. Moreover, a creel survey was conducted encompassing the same period to characterize the fish caught downstream. During the study, 770 lock cycles were completed, with 58,982 fish being observed in 234 cycles, mostly moving upstream. Eels (Anguilla anguilla) were the most numerous, being followed by the mugilids (Chelon ramada and Mugil cephalus). The number of fish using the lock was low from November to April, increasing from May to July, and was related to tide height, discharge at the powerplant tailrace, moon phase and time of day. Sea lamprey (Petromyzon marinus) and shads (Alosa spp.) were caught downstream of the dam but were never found using the lock. While more research is needed to assess the fate of the eels moving upstream, management of the anadromous taxa in the Douro River must rely on the last 20 km of the river.