Is there a threshold size regulating seaward migration of brown trout and Atlantic salmon?
Article first published online: 4 APR 2005
Journal of Fish Biology
Volume 42, Issue 4, pages 541–550, April 1993
How to Cite
ØKland, F., Jonsson, B., Jensen, A. J. and Hansen, L. P. (1993), Is there a threshold size regulating seaward migration of brown trout and Atlantic salmon?. Journal of Fish Biology, 42: 541–550. doi: 10.1111/j.1095-8649.1993.tb00358.x
- Issue published online: 4 APR 2005
- Article first published online: 4 APR 2005
- (Received 1 May 1992, Accepted 14 August 1992)
- Salmo salar;
- Salmo trutta;
- life history;
- intraspecific variation;
- ontogenetic habitat shift
We investigated the influence of variation in body size and growth rate on age of smolting in Atlantic salmon and brown trout in four different Norwegian rivers. In Atlantic salmon smolt ages varied between 2 and 6 years, and in brown trout between 2 and 7 years. Smolt age was negatively correlated with parr growth, and positively correlated with smolt size. Age at smolting was more variable in the two northern than the two southern rivers. Smolt sizes and ages were also more variable in brown trout than in Atlantic salmon. Based on the observed variation in smolt size and age, we reject the hypothesis that a threshold size alone regulates age at smolting. Within populations smolt age depends on growth rate so that fast-growing parr smolted younger and smaller than slow-growing parr. We hypothesize that smolt size and age is a trade-off between expected benefits and costs imposed by differences in individual growth rate.