Temporal variation in abundance, return rate and life histories of previously spawned Atlantic salmon in a large subarctic river

The 30 year time series analyses revealed large temporal variation in the return rates and a recent increase in abundance of previous spawning Atlantic salmon Salmo salar in the River Teno, northern Scandinavia. The mean proportion of repeat spawners was 7 and 4% in the total Atlantic salmon catch and 9 and 22% in multi-sea-winter (MSW) catch component for females and males, respectively. Previous spawners constituted on the average 7% of the catch in mass but up to 20%(31 t) and 30%(19 t) in 2003 and in 2004, respectively. In 1975-2000, the proportion of previous spawners varied between 1 and 6%(3-12% of MSW Atlantic salmon), whereas in 2001-2004, they accounted for 8-21%(16-35% of MSW Atlantic salmon) of the total Atlantic salmon catch. The number of previous spawners in the catch correlated significantly with the preceding numbers of respective 1-3 sea-winter (SW) maiden Atlantic salmon 2 years earlier. The recent increase in the numbers of 1S1 and 2S1 (1 or 2 years at sea followed by first spawning and 1 year reconditioning period at sea) alternate spawning Atlantic salmon was a consequence of higher numbers of maiden 1SW and 2SW Atlantic salmon in the catches and increased sea temperatures. Similarly, the return rate of 1SW Atlantic salmon to second spawning has improved in recent years. Most previous spawners ascended and were captured early in the fishing season. The smolt and sea-age combinations of repeat spawners comprised 68 age groups contributing with the annual mean of 15 age groups to the great diversity of the River Teno Atlantic salmon population complex.