Growth of Baltic salmon Salmo salar in the sea

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Abstract
Aspects of the growth of Baltic salmon S. salar L. are discussed. Results are mainly based on about 210,000 reports of recaptured salmon out of 1.7 million tagged smolts released between 1953 and 1980 from Swedish hatcheries. Tagged and unmarked salmon seem to have equal survival and growth rates in the Baltic Sea, as do wild and hatchery stock compared in 1 river. Results should be representative for the main part of the Baltic salmon population of which 70% now are of hatchery-reared origin. During the period in question no clear trend in growth rate can be seen. Drifnet selectivity in the dominating offshore fishery for feeding fish, mainly working during the 2nd winter in the sea when salmon reach catchable size, strongly affects size at higher ages. Comparisons with older data are therefore difficult to make. It is clear that growth rates of southern stocks have increased and those of the more numerous northern river stocks have decreased during the last 50 yr. This may have been caused by changed environmental rather than genetic factors probably acting during early life in the sea. Individual variation in growth rate is large and distributions of size at a certain age overlap between 3 age classes. Monthly mean weights of feeding salmon in the sea give a fairly good picture of growth but are influenced by gear selectivity and by spawning migrants leaving in spring being larger than average for their age class.