Survival of sea‐water‐adapted trout,Salmo trutta L. ranched in a Danish fjord |
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| Authors: | S S Pedersen G H Rasmussen |
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| Abstract: | The effect of seawater adaptation on the survival of coastally released post‐smolt trout, Salmo trutta L., was investigated by release: (1) directly (with no adaptation); (2) after retention in net pens in the sea for 29–131 days (delayed release); (3) after feeding with a high‐salt diet (12–13.5% NaCl) for 4 weeks; and (4) after a combination of (2) and (3). In total, 17 640 trout (age = 1+, 1.5 and 2+ years; mean fork lengths = 18.2–25.6 cm) were released in 14 batches in the summer or autumn months of 1986–1989. All fish were of domesticated origin and Carlin tagged. Survival and instantaneous mortality rates (total and fishing mortality) were estimated from reported recaptures. Mortality rates were estimated for: (1) the post‐smolt period; (2) the period until the legal size of capture (40 cm) was attained; and (3) for larger sea‐trout. Release with a delay of 4 weeks gave an increased survival rate. A longer adaptation period did not increase survival. On average, survival was increased by 36%. Survival was not increased by high‐salt diets. Until attainment of the legal size for capture, survival was 9.6% higher on average, with extremes as low as 1.7% and as high as 38% in individual batches. |
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| Keywords: | Carlin tagging post‐smolt sea‐ranching sea‐trout sea water adaptation survival |
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