Publications

History, Conservation and Management of Adfluvial Brown Trout Stocks in Finland

Syrjänen, J., Vainikka, A., Louhi, P., Huusko, A., Orell, P. & Vehanen T. 2017.

Adfluvial brown trout, Salmo trutta m. lacustris (L.), was common in all Finnish watercourses with large lakes at the beginning of the 20th century. Nowadays, the stocks are severely declined in central and southern Finland due to damming and dredging of riverine reproduction areas, organic pollution from the paper and pulp industry, and increasing river fishing. However, adfluvial brown trout is an iconic species in recreational fisheries, and is captured mainly by rod and line in rivers, and by gillnets and trolling in all large lakes. The importance of the species to commercial fishing in Finland is generally negligible. Unregulated lake fishing, mainly with gillnets, however, led to a severe collapse of the southern stocks from the 1960s to the 1990s. To compensate for the decline of wild stocks, stocking streams with eggs and fry was started at the beginning of the 20th century. From the 1970s onwards, this largely changed to extensive direct stocking into lakes of parr and smolts. Yet, the southern adfluvial brown trout stocks have not recovered, and catches of adfluvial brown trout in lakes are almost entirely based on stocking directly into lakes of 2-3 -year-old smolts derived from hatchery brood stocks. Lake Inari is now the only large lake with a significant (12-38 %) contribution of wild fish to the catch. Today, water quality in most large watercourses is suitable for brown trout, reproduction areas are being restored, and prey fish stocks in lakes are adequate. Mainly voluntary protection of wild individuals in river fishing began to spread from 2005, and wild adfluvial brown trout were finally protected by law in 2016 in southern Finland. However, along with the protection of the wild fish, the minimum size limit of 600?mm, imposed in 2014, was again decreased to 500?mm effectively preventing the recovery of wild stocks subject to intensive gillnet fishing. Based on a population model built for two important Finnish adfluvial brown trout stocks, the current fishing mortality rates need to be decreased substantially in order to rebuild the severely depleted stocks. The bycatch mortality of juvenile fish should be minimized and the minimum size limit kept at 600?mm or more. Bag limits and obligatory catch-and-release provide management measures to further decrease fishing mortality.Adfluvial brown trout, Salmo trutta m. lacustris (L.), was common in all Finnish watercourses with large lakes at the beginning of the 20th century. Nowadays, the stocks are severely declined in central and southern Finland due to damming and dredging of riverine reproduction areas, organic pollution from the paper and pulp industry, and increasing river fishing. However, adfluvial brown trout is an iconic species in recreational fisheries, and is captured mainly by rod and line in rivers, and by gillnets and trolling in all large lakes. The importance of the species to commercial fishing in Finland is generally negligible. Unregulated lake fishing, mainly with gillnets, however, led to a severe collapse of the southern stocks from the 1960s to the 1990s. To compensate for the decline of wild stocks, stocking streams with eggs and fry was started at the beginning of the 20th century. From the 1970s onwards, this largely changed to extensive direct stocking into lakes of parr and smolts. Yet, the southern adfluvial brown trout stocks have not recovered, and catches of adfluvial brown trout in lakes are almost entirely based on stocking directly into lakes of 2-3 -year-old smolts derived from hatchery brood stocks. Lake Inari is now the only large lake with a significant (12-38 %) contribution of wild fish to the catch. Today, water quality in most large watercourses is suitable for brown trout, reproduction areas are being restored, and prey fish stocks in lakes are adequate. Mainly voluntary protection of wild individuals in river fishing began to spread from 2005, and wild adfluvial brown trout were finally protected by law in 2016 in southern Finland. However, along with the protection of the wild fish, the minimum size limit of 600?mm, imposed in 2014, was again decreased to 500?mm effectively preventing the recovery of wild stocks subject to intensive gillnet fishing. Based on a population model built for two important Finnish adfluvial brown trout stocks, the current fishing mortality rates need to be decreased substantially in order to rebuild the severely depleted stocks. The bycatch mortality of juvenile fish should be minimized and the minimum size limit kept at 600?mm or more. Bag limits and obligatory catch-and-release provide management measures to further decrease fishing mortality.

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