(Salmo Trutta) During Rapid Flow Decreases Caused by Hydropeaking
REGULATED RIVERS: RESEARCH & MANAGEMENT Regul. Ri6ers: Res. Mgmt. 17: 609–622 (2001) DOI: 10.1002/rrr.652 FIELD EXPERIMENTS ON STRANDING IN JUVENILE ATLANTIC SALMON (SALMO SALAR) AND BROWN TROUT (SALMO TRUTTA) DURING RAPID FLOW DECREASES CAUSED BY HYDROPEAKING S.J. SALTVEITa,*, J.H. HALLERAKERb, J.V. ARNEKLEIVc AND A. HARBYb a Freshwater and Inland Fisheries Laboratory (LFI), Natural History Museums and Botanical Garden, Uni6ersity of Oslo, Box 1172, Blindern, 0318 Oslo, Norway b SINTEF Ci6il and En6ironmental Engineering, Department of Water Resources, 7465 Trondheim, Norway c Freshwater and Inland Fisheries Laboratory (LFI), Norwegian Uni6ersity of Science and Technology, 7491 Trondheim, Norway ABSTRACT Field experiments showed that sudden reductions in river flow may cause high mortality of juvenile salmonids through stranding. A 75-m2 enclosure in the drawdown zone of a regulated river was stocked with a known number of wild 0+ and/or 1+ wild Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). The number stranded was estimated by counting the surviving fish collected in a bag as they left the enclosure. In general, a far higher incidence of fish stranding was found during winter conditions (B4.5°C) compared with the higher temperatures during late summer and early autumn. This is probably mainly because of lower fish activity during the cold season and a substrate seeking behaviour especially during daytime. Stranding was lower at night, probably because of a predominant night active behaviour. Hatchery salmon behaved oppositely to wild fish, and studies based on cultivated fish may give wrong conclusions as to the consequences of hydropeaking. Searching for fish in the substrate underestimated the consequences of sudden flow reductions, as fish were difficult to find.
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