The smolt run and postsmolt survival of Atlantic salmon, Salmo salar L., in relation to early summer water temperatures in the northern Baltic Sea

Abstract

The smolt run and postsmolt survival of Atlantic salmon, Salmo salar L., in relation to early summer water temperatures in the northern Baltic Sea Un resumen en españ ol se incluye detrás del texto principal de este artículo.

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“…Timing of seaward migration is modulated by temperature and fl ow, and perhaps the lunar cycle (Wedemeyer et al 1980 ;McCormick et al 1998 ;Jutila et al 2005 ;Thorstad et al 2011 [Chapter 1 ]; Fig. 16.5 ).…”

“…Higher temperatures may advance the smolt run timing but photoperiod will presumably also restrict advancement. Jutila et al (2005) reported the main smolt run in a northern Baltic river to be abbreviated in years when migration was delayed by freshwater conditions, and they also showed that early summer SST which is either too low ( < 9 ° C) or too high ( > 12 ° C) at entry was detrimental to post -smolt survival. Because very early post -smolt mortality is typically high (Klemetsen et al 2003 ), the implications are that timing of seawater entry has consequences for metabolic costs, physiological stress, prey availability and the likelihood of predation ).…”

“…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. 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.…”

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“…Water temperature partly regulates fish migrations by determining the direction of migration or stimulating the initiation of migratory activity and combines with other stimuli, such as discharge and photoperiod (McFarland, 1971;Northcote, 1984Northcote, , 1998Crisp 1996). The main factor initiating downstream migration of smolt (Jutila et al, 2005) is a rise in water temperature to over 10°C. This did not happen in 2003 when the temperature ranged from 4.3-12.3°C, whereas in 2004 temperatures were higher (9.6-16.1°C).…”