Restoring migratory salmonid populations in regulated rivers in the northernmost Baltic Sea area, Northern Finland - biological, technical and social challenges

Abstract

SummaryThis paper summarizes the objectives, activities initiated and approaches used in developing Atlantic salmon stock rebuilding programmes in three large river systems in northern Finland in order to identify the priorities for research and management for further restoration and rehabilitation steps. Until recently, these historically renowned major salmon rivers have been harnessed for hydropower for 40-60 years without provisions for fish passage. Hydropower companies are obliged to compensate for the losses caused by dam construction by annual fish releases, including juveniles of Atlantic salmon and migratory brown trout. Returning fish are harvested in the designated Ôterminal fishery areasÕ at river mouths. Recently, activities aimed at restoring salmonid stocks have started in all these rivers. First fishways at the dams closest to the river mouths were constructed on two rivers, and preliminary projects were completed to review the preconditions for restoration, options for bypassing the dams, and to study the performance of these fishways. New projects incorporating further detailed fishway planning are underway. The various projects have proved successful in bringing together authorities, hydropower companies, local organizations, and expertise from various institutions for a joint effort to tackle these multifaceted and multidisciplinary problems.

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“…Karppinen et al 2002, Erkinaro et al 2011, Marttila et al 2014 led to intensive construction of dams on large river systems so that today there are only 2 undammed large river channels (Simojoki and Tornionjoki) within the Finnish part of the Baltic Sea drainage. Because equipping the hydropower plants with fishways has been very rare (Karppinen et al 2002, Erkinaro et al 2011, Marttila et al 2014, the hydro-electricity production has caused the occurrence of anadromous salmonids to collapse as the dams have prevented their natural spawning migration to these rivers. The lack of salmonids in dammed rivers has been compensated by annual stocking of farmed brown trout above the dams, the fish originating from both local (sympatric with FPM) and non-local (allopatric with FPM) strains (Luhta andMoilanen 2006, Hiltunen 2010).…”

“…in the River Iijoki area to support the traditional activity, salmonid fishing (Luhta andMoilanen 2006, Hiltunen 2010). However, Atlantic salmon have been stocked only to estuaries near the sea, and thus below the dams (Erkinaro et al 2011, Marttila et al 2014, where they cannot migrate to the rivers. Above the dams, attempts have been made to maintain salmon populations via sporadic egg stocking and translocating adult salmon to upstream (see e.g.…”

“…Above the dams, attempts have been made to maintain salmon populations via sporadic egg stocking and translocating adult salmon to upstream (see e.g. Erkinaro et al 2011). However, the salmonid species in the former spawning grounds of Atlantic salmon has in practice changed from salmon to brown trout due to the dam construction and the subsequent stockings.…”

“…Conspicuously, no single variable was higher in brown trout than in salmon in any experiment or comparison (Table 5). The adaptation of FPM to salmon in the large channels Luttojoki and Livojoki, the catchments of both of which were dammed over 50 years ago (Karppinen et al 2002, Erkinaro et al 2011, together with the general salmonid stocking practices favouring brown trout as the compensatory species, provides an additional explanation for the collapse of FPM populations, as well as for the lack of successful recruitment of FPM, in large Finnish salmon rivers (Valovirta 1990, Oulasvirta 2011. As there are hardly any functioning fishways in the dams in Finland, the appropriate host, Atlantic salmon, has had no chance to naturally migrate to its original spawning grounds after the dam construction.…”

“…The lack of the anadromous salmonids, including salmon, has been ordered by the courts to be compensated via annual release of farmed salmonids (e.g. Erkinaro et al 2011), but there have been no strict requirements for the salmonid species used in these stockings. Thus, the former spawning habitats of Atlantic salmon for example in the Iijoki area are now dominated by brown trout, while salmon juveniles have been released only to estuaries near the sea, i.e.…”