Selection experiments on Atlantic salmon ranching. II. Variation among release sites and strains for return rate, body weight and ratio of grilse to total return

Abstract

A Nordic project ‘Salmon Ranching—Possibilities of Selective Breeding’ started in Iceland in 1987. The aim of the project was to study the possibilities for breeding and selection in sea ranching of Atlantic salmon. Smolts from six salmon strains were released from four different release sites in three year-classes. Performance was estimated for return rate, body weight, ratio of grilse to total return and total biomass per 1000 smolts released, which gives a measure of total yield after 2 years at sea. In general, total return rate was low during the experiment, ranging from 3.04% to 0.96% between year-classes. The mean body weights of grilse and two-sea-winter salmon were 2.4 kg and 6.2 kg, respectively. Biomass per 1000 smolts released ranged from 35.6 kg to 87.5 kg between year-classes. Significant differences were observed among the salmon strains for all traits tested. In general, strains used for salmon ranching in Iceland gave the highest yield in total biomass compared with other strains tested; up to three-fold differences were observed. Return rates differed among release sites, with the highest return rates observed at the Kollafjör∂̵ur release site, where smolts were released from a riverine trap, compared with releases directly from concrete tanks at Vogavík or from net pens at Silfurlax ranching stations. For the 1991 year-class, 94.0 kg total biomass returning was observed at the Kollafjör∂̵ur release site compared with 52.7 kg at Vogavík and 75.3 kg at Silfurlax. Similar differences in return rates were observed between Kollafjör∂̵ur and the Lárós release site, where the smolts were released from netpens into a freshwater lake. Significant interactions between salmon strain and release site were detected for total return rate and the ratio of grilse to total return, but not for body weight of grilse. This resulted in a change in the order of ranking of the strains at different release sites, especially in year-class 1989. This interaction needs further examination.