Fish impingement at estuarine power stations and its significance to commercial fishing

Abstract

The abstraction of cooling water at power stations sited on tidal waters inevitably leads to mortalities of some fish which are drawn in with the cooling water supply and become impinged on the intake screens. These fish are predominantly 0‐ or I‐group juveniles which, owing to their small size, are unable to resist intake currents.Commercial fishermen often object to the fact that juvenile fish are killed in this way. Their concern stems from the fact that, in order to protect stocks, commercial fishing is restricted to fish which are above a statutory minimum landing size, whereas the majority of fish killed by impingement are below this size.This paper considers the significance of impingement mortalities at estuarine sites in Britain for six commercially important species: cod, Gadus morhua, whiting, Merlangius merlangus, plaice, Pleuronectes platessa, dab, Limanda limanda, sole, Solea solea and herring, Clupea harengus. Life tables are used to establish expected survival trajectories for each species and to compute reproductive potential. Each fish killed on intake screens is then considered in terms of the fraction of the reproductive potential of a single adult at maturity, and is ascribed an ‘adult equivalent’ value. Total catches of mixed juveniles and adults are then presented as ‘adult equivalent’ values. The results are then compared with commercial landings data and it is shown that catches by power stations are trivial in comparison with commercial landings.