Association between environmental factors, smolt size and the survival of wild and reared Atlantic salmon from the Simojoki River in the Baltic Sea

Abstract

The survival of Atlantic salmon Salmo salar in the Baltic Sea was examined in relation to smolt traits (length and origin) and annual environmental factors [sea surface temperature (SST) and seasonal North Atlantic Oscillation (NAO) index], and prey fish abundance (herring Clupea harengus and sprat Sprattus sprattus) in the main basin and the southern Gulf of Bothnia. The study was based on recapture data for Carlin-tagged hatchery-reared and wild smolts from the Simojoki, a river flowing into the northern Gulf of Bothnia. The survival of the wild and reared groups was analysed using an ANOVA model and a stepwise regression model, with the arcsintransformed proportion of recaptured fish as the response variable. The results demonstrated a combined influence of smolt traits and environmental factors on survival. For the reared Atlantic salmon released in 1986-1998 (28 groups), the increasing annual mean SST in July in the southern Gulf of Bothnia and increasing mean smolt size improved survival. If the SST in July was excluded from the model, the NAO index in May to July also had a positive effect on survival (P < 0Á10). The log 10 -transformed abundance of 0þ year herring in the southern Gulf of Bothnia entered the model (P < 0Á15) if the SST and NAO index were excluded. For the wild Atlantic salmon released in 1972-1993 (21 groups), only the increasing SST in July showed a significant association with improved survival (P ¼ 0Á004). Prey fish abundance in the main basin of the Baltic Sea had no influence on the survival of reared or wild smolt groups. The interaction between smolt size and the SST in July was not significant. The origin was a better, but not a significant, predictor of marine survival compared to the smolt size or the SST in July. The mean recapture rate of the wild groups was twice that of the reared groups in the whole data. The results suggest that cold summers in the Gulf of Bothnia reduce the survival of young Atlantic salmon in both wild and reared groups. The larger smolt size of the reared groups compared with the wild groups to some extent compensated for their lower ability to live in the wild. # 2004 The Fisheries Society of the British Isles

Getting into Hot Water? Atlantic Salmon Responses to Climate Change in Freshwater and Marine Environments

“…But signifi cant correlations with the NAO have not always been the outcome. For example, for hatchery -reared and wild Baltic post -smolts, Kallio -Nyberg et al (2004) found no correlation between the NAO and survivorship of wild smolts, but did note a positive correlation between year -class survivorship and July SST -immediately after smolt entry to sea water -perhaps indicating a detrimental effect of cold summers. Similarly, Niemel ä et al (2004) found no correlation between the NAO and salmon catches in the rivers Teno and Naatamojoki (northern Finland), the stocks of which migrate to the Barents Sea and show large natural fl uctuations.…”

“…Direct physiological effects of temperature have often been inferred, especially for smolts fi rst entering sea water (e.g. Narayanan et al 1995 ;Kallio -Nyberg et al 2004 ;Jutila et al 2005 ; Section 16.6 ), and the importance of indirect effects -perhaps manifest as ' bottom -up ' impacts through alterations in prey availability -has long been suspected or observed (e.g. Todd et al 2008 ).…”

“…Kallio -Nyberg et al 2004 ;Lacroix & Knox 2005 ), but its infl uence for wild smolts has been poorly studied and remains unclear. In the Baltic Sea, Jutila et al (2005) and Kallio -Nyberg et al (2004) found that the typically larger size of hatchery individuals may, to some extent, compensate for their origin in comparison to wild smolts.…”

“…Kallio -Nyberg et al 2004 ;Lacroix & Knox 2005 ), but its infl uence for wild smolts has been poorly studied and remains unclear. In the Baltic Sea, Jutila et al (2005) and Kallio -Nyberg et al (2004) found that the typically larger size of hatchery individuals may, to some extent, compensate for their origin in comparison to wild smolts. Friedland et al (2009) report on data for two wild stocks monitored over a period of highly contrasting survival rates: for the River North Esk (Scotland), smolt size clearly had no infl uence on resultant survival rate, whereas for the River Figgjo (Norway), survival rate was correlated with size at sea entry.…”

Effects of smolt size and timing of migration on recovery rate of wild masu salmon Oncorhynchus masou

“…Knowledge of the ecology of wild salmon is important to improve enhancement and management techniques because wild salmon populations have evolved to adapt to the environmental conditions of the local area. These same factors affecting the marine survival of wild salmon have also been investigated [10][11][12][13][14][15][16]. The timing of smolt migration varies with species, age, latitude, and the specific estuarine-coastal area [17,18], which is thought to be population specific [19], and the timing of seaward migration and ocean entry also strongly affect the survival of smolts.…”