Browsing Proceedings & Conference papers by Author "Willis, S. E."
Spring salmon enhancement on the Delphi Fishery, IrelandMcDermott, T. J.; Willis, S. E.; Mantle, P. (Atlantic Salmon Trust, 1996)This paper summarises the results of an Atlantic salmon (Salmo salar) enhancement programme on the Delphi Fishery in the west of Ireland between 1991 and 1995. The aim of the programme was to increase salmon rod catches in the wake of a sea trout stock collapse. Smolts from two other Irish rivers, Burrishoole and Corrib, were released alongside Delphi fish and differentially tagged. Record angling catches were subsequently recorded. Catch rates varied from 0.6 to 12.7 per 1,000 smolts released. The comparative performance of the different stocks is assessed, with significant differences emerging between the stocks and between year classes In terms of survival/exploitation rates, run limes, sex ratios and homing patterns. The Delphi fish produced consistently lower overall returns than the Burrishoole groups, but consistently much higher numbers of early-running multi-sea-winter (MSW) salmon. These MSW salmon were predominantly female, while Delphi grilse were predominantly male. The Corrib fish performed relatively poorly. The smaller MSW salmon component of the non-indigenous groups ran later in the season than their Delphi counterparts. Important size differences in adult returns were noted and related to stock, sex, husbandry and selection by interceptory fisheries. It is suggested that the MSW salmon component of Delphi stocks is attributable to genetic factors, possibly linked to low freshwater temperature regimes. The programme has contributed to an increase in estuarine droll netting. Exploitation of grilse by all forms of coastal net ranged from 56% to 87%. Exploitation of MSW salmon by nets was lower, ranging from 0% to 54%, the lowest rates being achieved by the early-running Delphi MSW salmon. The programme is expensive and cannot be justified in terms of direct angling revenue. But when related accommodation income is taken into account, the financial results and the sustainment of the fishery's capital value broadly justify the programme to date.