Behavioural study of downstream migrating eels by radiotelemetry at a small hydroelectric power plant
Biology, Management, and Protection of Catadromous Eels
American Fisheries Society
Eels, because of their size and life cycle, are among the most vulnerable species regarding the presence of obstacles on waterways. During a study of the efficiency of two types of fish passes, the behaviour of migrating European eels (Anguilla anguilla) was investigated using telemetry and trapping at a small hydroelectric power plant (southwest of France). Radiotracking was conducted manually and by stationary receivers in the turbine area and downstream and upstream from the power plant. Sixteen eels were tagged by surgical implantation of transmitters and released upstream of the power station. Results provide insight on eel behaviour during the downstream run (swimming rates and delayed migration) as well as behaviour in front of both exits to the trap. Almost all tagged individuals moved upstream after the release. Most of these eels migrated downstream after a heavy rainfall, avoiding the power station by crossing the overflowing dam. They were tracked down to the estuary (16 km) over several days during which time several periods of non-movement occurred. Descending non-tagged eels transiting through either of the two tested forebay bypasses were trapped. Daily catches corresponded to movements of radio-tagged individuals. Environmental parameters were recorded and compared to the downstream run. Results clearly showed that silver eel migration was closely linked to certain environmental parameters (flow rate, turbidity, and luminosity) and that downstream migration is inhibited if favourable environmental conditions are not met, such as during daytime when turbidity is low. Direct comparison of daily catches through the bottom and surface bypasses as well as observations of radio-tagged eels in the forebay both suggest that a bottom bypass may be appropriate for safely transiting downstream migrating eels.