The behavioural response of river lamprey (Lampetra fluviatilis) to two types of experiment weir.

Kemp, P.S., Tsuzaki, T., Russon, I.J, Moser, M., Muller, G.U. and Lucas, M. (2007) The behavioural response of river lamprey (Lampetra fluviatilis) to two types of experiment weir. Sixth International Ecohydraulics Symposium, Christchurch, New Zealand. 18 - 23 Feb 2007.

Abstract

Several populations of river lamprey have declined across Europe over recent years and have been extirpated in some rivers. As a result, this species is protected under Annex II of the European Habitats and Species Directive. An inability of this relatively weak swimming anadromous fish to negotiate in-river impediments, such as weirs, during their spawning migration has been cited as an explanation for their decline. The ability of 100 upstream migrating lamprey to negotiate either an undershot or overshot weir was assessed using an experimental flume at night. Under infrared illumination, ten trials were conducted over 3 flows in which the approach and passage over or under the weir was recorded using overhead video cameras. Distinctly different fine-scale hydraulic conditions associated with the two weir configurations were mapped by hydraulic engineers. In an attempt to bridge the gap between fluid dynamics and fish behaviour, the response of the lamprey to the hydraulic conditions encountered was investigated. Passage efficiency was negatively related to discharge and velocity and more likely when an undershot weir was used, although fish were observed to pass over the crest of the weir against velocity of 1.5 m s-1. The lamprey were observed to follow routes of “least resistance” and to alter their behaviour in relation to weir type. The findings have important implications for the design of fish passage facilities for this species.

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Contributors

Author: P.S. Kemp

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