Repeatable individual variation in migration timing in two anadromous salmonids and ecological consequences

Area of Science:

• Behavioral Ecology
• Animal Migration
• Population Dynamics

Background:

• Individual differences in behavior are common in animals.
• Few studies examine the long-term consequences of consistent behaviors in wild populations.

Purpose of the Study:

• To investigate the consistency of migration timing in Arctic char and brown trout.
• To determine the ecological and fitness consequences of consistent individual variation in migration timing.

Main Methods:

• Utilized 25 years of data from over 27,000 Carlin-tagged anadromous fish (Arctic char and brown trout).
• Analyzed migration timing to and from the sea over multiple years (up to 13 successive years).
• Assessed impacts on growth, specific growth rate, longevity, maturity timing, and lifetime fecundity.

Main Results:

• Consistent individual differences in migration timing (seaward and freshwater ascent) were observed across multiple years.
• Early migrants showed greater mass increase and higher specific growth rates compared to late migrants.
• Early migration correlated with earlier maturity in both species, and increased longevity in Arctic char and lifetime fecundity in brown trout.

Conclusions:

• Repeatable individual variation in migration timing is a significant factor in the wild.
• Migration timing consistency has profound ecological and fitness consequences, influencing growth, longevity, maturity, and reproductive success.
• These findings highlight the importance of individual behavioral consistency in shaping population dynamics and evolution.