Effect of fishing regulation on the occurrence of repeat spawners and age distribution of Atlantic salmon in a northern Baltic river

• Published in: Fisheries management and ecology 2005-10, Vol.12 (5), p.341-347
• Main Authors: JOKIKOKKO, E., JUTILA, E.
• Format: Article
• Language: English
• Subjects: Brackish; fishing regulation; grilse; repeat spawning; Salmo salar
• ISSN: 0969-997X; 1365-2400
• DOI: 10.1111/j.1365-2400.2005.00457.x

Upstream migrating Atlantic salmon, Salmo salar L., were trapped annually between 1990 and 2003 at the mouth of the River Simojoki in the northern part of the Gulf of Bothnia, the Baltic Sea, to collect hatchery brood fish. They were also collected between 1996 and 1998 in the river to estimate the number of ascending salmon. These data on spawners were used to study the effect of changing fishing regulations in the Finnish coastal fishery in the mid‐1990s on the structure of the spawning stock. In total, 1.9% of 2290 multi‐sea‐winter adults had previously spawned. The average annual proportion of repeat spawners was 0.5% between 1990 and 1996, but significantly higher (2.8%) between 1997 and 2003. The age distribution also changed significantly, as 4SW and 5SW salmon appeared in the population in the latter years. These changes were most probably due to the application of stricter fishing regulations. The potential of salmon to spawn repeatedly was thus preserved, despite a severe decline in natural production in the 1980s and early 1990s.