Annual variability in survival of sea‐ranched Baltic salmon, Salmo salar L: significance of smolt size and marine conditions

Abstract

Carlin tagging data for 1980–1991 were used to examine the influence of smolt size and feeding conditions on the post‐smolt survival of ranched River Neva salmon, (Salmo salar L.), in the the Gulf of Finland, which is the native feeding area of the stock, and in the Bothnian Sea, where the stock has been introduced. Because of better feeding conditions, the survival rates were higher and less variable in the Gulf of Finland than in the Bothnian Sea. In the Bothnian Sea, the annual variability in survival decreased and the mean value increased with increasing smolt size from the smallest (14–16 cm) to the largest (28–30 cm) size classes. The survival was positively correlated with growth rates, food resources and sea‐surface temperatures. This suggests that in the Bothnian Sea the annual variability in survival is mainly because variable marine conditions affect growth rates, and, thus, the vulnerability of the post‐smolts to size‐dependent predation. In the Gulf of Finland, the survival advantage of large initial size and rapid growth was counteracted by size‐selective post‐smolt mortality from fishing. The increase in the survival rate with increasing smolt size levelled off at 22 cm, and the correlations between survival, growth and the indices of feeding conditions were mostly insignificant. For large smolts, some negative correlations were recorded, suggesting that the relative significance of mortality from fishing may even exceed that of size‐dependent natural mortality. The implications of the results for management are discussed.

Survival of reared Atlantic salmon and sea trout in relation to marine conditions of smolt year in the Baltic Sea

“…Warm surface waters increase, but cold waters decrease the survival of post-smolts of Atlantic salmon during the time of year when the smolts enter the sea (Friedland et al, 1993(Friedland et al, , 2000 or later in summer (Salminen et al, 1995;Kallio-Nyberg et al, 2004). During the period 1970-2001 followed in this study, there was a weak decline in the SST.…”

“…This may be explained by the positive covariation of these abundance levels. The association between the high survival of salmon and high 0+ herring recruitment in the Bothnian Sea has earlier been reported for Neva salmon released into the Bothnian Sea (Salminen et al, 1995) and for Simojoki salmon originating from the Bothnian Bay . The dependence of Atlantic salmon survival on the abundance of young herring was expected in the Gulf of Bothnia, where only herring dominate in the diet of the piscivorous Atlantic salmon (Salminen et al, 2001).…”

“…The best feeding areas for salmon in the Baltic Sea are situated in the Main Basin, over 500 km from the Bothnian Bay estuaries. The majority of the salmon originating from the Bothnian Bay migrate to the Main Basin, if the recruitment of young herring is weak in the Gulf of Bothnia (Salminen et al, 1995;Kallio-Nyberg et al, 1999). The salmon is thus able to change its feeding distance according to spatial distribution of its main prey items.…”

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

“…Since the late 1970s, hatchery-reared salmon smolts (Salmo salar) have regularly been released into the estuaries of the Gulf of Bothnia and the Bothnian Sea in the Baltic Sea (Salminen et al, 1995(Salminen et al, , 2004 to enhance local salmon fisheries. Stocking has been carried out with salmon of the Neva stock, because the original stocks of these Finnish coastal areas were driven to extinction in the early 2000s (Salminen et al, 2007).…”

Early maternal experience shapes offspring performance in the wild

“…For example, although SEG juveniles smolt later than faster growing females, they tend to do so at a larger body size (Økland et al 1993). In Atlantic salmon, smolt size within a cohort is related positively to ocean survival (Salminen et al 1995, Saloniemi et al 2004). Thus, a larger size at smolting (and higher survival probability at sea) might offset (to an extent) the cost of delayed seaward migration and likely greater instream mortality.…”