Contents of volume 43

Abstract

Windermere, the largest natural lake in England, is divided by shallows and islands into North and South Basins. The lake supports an important sports fishery for Arctic charr, Salvelinus alpinus (L.), with some of the catches sold locally. The chief objectives of this comparative study were: (i) to examine the relationships between data obtained by three sampling methods (gill-nets, angling, hydroacoustic surveys), (ii) to discover if the simpler methods of gill-netting or anglers’ catches provided an adequate method for assessing the charr stock compared with the more extensive echo-sounding (hydroacoustic methods). There was a significant correlation (r=0.59, P<0.01) between the annual catch per unit effort (CPUE) for two anglers. The annual CPUE for angler A, but not for angler B, for the whole lake correlated significantly (r=0.41, P<0.05) with the gill-net CPUE for one site in the North Basin, but the relationship for both the anglers was not significant (P>0.05) when only the catches for the North Basin were used in the comparisons. Gill-net CPUE for one site in the North Basin correlated significantly (r=0.85, P<0.01) with the annual mean density of large (length>20cm) pelagic fish in both the North Basin and the whole lake, both densities being estimated by hydroacoustic methods. Anglers’ catches (annual CPUE for angler A and B) for the whole lake and for the North Basin, but not the South Basin correlated significantly (r=0.80–0.90, P<0.01) with the annual mean density of large pelagic fish in the upper water layers (depth<20m) during the day. It was concluded that both gill-net and anglers’ CPUE could be used as an approximate annual index of abundance for the charr stocks for the whole lake; and for the North, but not the South Basin of the lake, they were not as reliable as the more extensive hydroacoustic methods.