The survival of semi‐wild, wild and hatchery‐reared Atlantic salmon smolts of the Simojoki River in the Baltic Sea

Abstract

The recapture rate and survival of hatchery-reared Atlantic salmon Salmo salar stocked as 1 year-old parr (semi-wild) with that of hatchery-reared Atlantic salmon stocked as 2 year-old smolts and wild smolts of Atlantic salmon in the northern Baltic Sea were compared. This was done through tagging experiments carried out in 1986-1988 and 1992. The recapture rate of the semi-wild groups varied from 1Á0 to 13Á1%, being similar in 3 tagging years and lower in 1 year than that of the wild groups (1Á7-17Á0%). The recapture rate of the semi-wild groups was similar (in 2 years) or higher (in 2 years) than that of the hatchery-reared groups stocked as smolts (1Á3-6Á3%). The survival of semi-wild smolts during the sea migration was as high as that of wild Atlantic salmon of an equal size and two to three times higher than hatchery-reared Atlantic salmon stocked as smolts. The survival rate was positively associated with smolt size. The suitability of hatchery-reared parr and smolts in the management of reduced Atlantic salmon stocks is compared.

Effect of hatchery rearing and environmental factors on the survival, growth and migration of Atlantic salmon in the Baltic Sea

“…One consequence of the less adaptive behaviour of the reared smolts is that they suffer high natural mortality in their first weeks at sea (Dieperink et al, 2002). The problems in marine survival of the reared salmon observed in this study are consistent with earlier observations (Finstad and Jonsson, 2001;Jonsson et al, 2003;Saloniemi et al, 2004;Jokikokko et al, 2006).…”

“…Effort has been put into avoiding intentional selection in hatcheries, and the ultimate goal of rearing has been to produce juveniles able to return and to reproduce without assistance. Short-term problems in physiological traits have been anticipated, as shown here and in many other Simojoki salmon studies (Jutila et al, 2003a;Saloniemi et al, 2004;Jokikokko et al, , 2006.…”

“…The descending wild and semi-wild smolts have been tagged at a trap near the river mouth in May and June during the natural smolt migration Jutila et al, 2005;Jokikokko et al, 2006). Wild smolts have not been tagged in all years due to the weak status of the salmon stock, while the tagging of semi-wild smolts was mainly carried out in 1999-2004.…”

Marine survival of reared Atlantic salmon in the Baltic Sea: The effect of smolt traits and annual factors

“…In hatchery-reared Atlantic salmon, marine survival is generally positively linked to smolt length (e.g., Vehanen et al, 1993;Saloniemi et al, 2004;Jokikokko et al, 2006). The survival advantage of large smolts over the smaller ones has been explained by their better ability to bear handling and tagging (Hansen, 1988), by their lower vulnerability to size-dependent predation (Hyvärinen and Vehanen, 2004) and, in the Bothnian Sea, also by their better ability to utilize food resources available in the area (Salminen et al, 2001).…”

“…This suggests that wild smolts have been better in coping with the changing environment compared to reared ones. Due to genetic, phenotypic and behavioural differences in life-history traits (Thorpe, 1991;Fleming et al, , 2002Fleming and Einum, 1997;Dieperink et al, 2002), wild salmon generally tend to have a higher lifetime success in nature (Fleming et al, 2000) and higher survival at sea than reared salmon (Jonsson et al, 2003;Saloniemi et al, 2004;Jokikokko et al, 2006;Jonsson and Jonsson, 2006). Recent findings suggest that the adaptation of salmonids to the rearing environment is very rapid, causing accelerated genetic differentiation of adaptive traits and a fast decline in the cumulative fitness of reared fish in the wild (Araki et al, 2007).…”