Abstract
Data from a 25-year study of anadromous Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) in the River Halselva provided evidence that survival during winter was linked to marine growth during the previous summer. The study supported the “critical size and critical period” hypothesis, which postulates that regulation of the abundance of adult salmonids occurs in two major phases. The first phase is marine mortality that occurs shortly after smolts enter salt water, and the second is during the following winter, when individuals that have not attained a critical size are unable to meet minimum metabolic requirements and die. In the present study, growth during summer appeared to be more important to winter survival than body size. Size-selective mortality occurred both at sea during summer and in fresh water during winter and was more evident for first-time migrants than repeat migrants.
Highlights
It is generally accepted that animals need to gain mass and store enough energy during periods of the year with rich food supplies to survive periods of the year with lower food availability (Rogers and Smith 1993; Hutchings et al 1999; Farley et al 2007; Hurst 2007)
The present study provides evidence that survival of anadromous Arctic char and brown trout during winter is linked to growth during the previous summer at sea
High growth rates at sea during summer resulted in increased survival in fresh water during the following winter
Summary
It is generally accepted that animals need to gain mass and store enough energy during periods of the year with rich food supplies to survive periods of the year with lower food availability (Rogers and Smith 1993; Hutchings et al 1999; Farley et al 2007; Hurst 2007). For teleost fishes in temperate and alpine areas, winter is considered a survival bottleneck (Johnson and Evans 1991; Cunjak et al 1998; Cunjak and Therrien 1998), with energy deficiency being the primary cause of mortality (Finstad et al 2004; Hurst 2007). Reviewing size-selective mortality in the juvenile stage of teleost fishes, Sogard (1997) found overwhelming evidence from field and laboratory studies that size-selective mortality occurs during winter, and larger members of a cohort are better than smaller members and conspecifics at tolerating physical extremes and enduring longer periods without food. Size-selective mortality may depend on the predator field, but compared with large fish, smaller fish are typically susceptible to a broader spectrum of predators and experience higher mortality rates (Sogard 1997).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
