Effects of emergence time and early social rearing environment on behaviour of Atlantic salmon: consequences for juvenile fitness and smolt migration.

Martin H Larsen,Jörgen I Johnsson,Jonathan D Midwood,Per-Ove Thörnqvist,Alexander D M Wilson,Erik Höglund,David Hammenstig,Kim Aarestrup,Svante Winberg,Hanping Wang

doi:10.1371/journal.pone.0119127

Abstract

Consistent individual differences in behaviour have been well documented in a variety of animal taxa, but surprisingly little is known about the fitness and life-history consequences of such individual variation. In wild salmonids, the timing of fry emergence from gravel spawning nests has been suggested to be coupled with individual behavioural traits. Here, we further investigate the link between timing of spawning nest emergence and behaviour of Atlantic salmon (Salmo salar), test effects of social rearing environment on behavioural traits in fish with different emergence times, and assess whether behavioural traits measured in the laboratory predict growth, survival, and migration status in the wild. Atlantic salmon fry were sorted with respect to emergence time from artificial spawning nest into three groups: early, intermediate, and late. These emergence groups were hatchery-reared separately or in co-culture for four months to test effects of social rearing environment on behavioural traits. Twenty fish from each of the six treatment groups were then subjected to three individual-based behavioural tests: basal locomotor activity, boldness, and escape response. Following behavioural characterization, the fish were released into a near-natural experimental stream. Results showed differences in escape behaviour between emergence groups in a net restraining test, but the social rearing environment did not affect individual behavioural expression. Emergence time and social environment had no significant effects on survival, growth, and migration status in the stream, although migration propensity was 1.4 to 1.9 times higher for early emerging individuals that were reared separately. In addition, despite individuals showing considerable variation in behaviour across treatment groups, this was not translated into differences in growth, survival, and migration status. Hence, our study adds to the view that fitness (i.e., growth and survival) and life-history predictions from laboratory measures of behaviour should be made with caution and ideally tested in nature.

Highlights

In recent years, it has become increasingly recognized that individuals within a population can differ consistently in suites of correlated behavioural traits across time and context
At 141 day degrees post fertilization (DDF), eyed eggs were placed into eight artificial spawning nests, which allowed fry to be sorted with respect to emergence time
principal component (PC) boldness reflects the degree of boldness displayed by an individual and it was dominated by three variables; number of entries and duration of visits to the novel object zone were positively associated with one another, but negatively associated with the latency to enter the zone (Table 3)

Summary

Introduction

It has become increasingly recognized that individuals within a population can differ consistently in suites of correlated behavioural traits across time and context. The time to emerge from the gravel may vary by several weeks among individuals in the same spawning nest [18,19] Those that emerge first from the nest are generally considered to have a competitive advantage over later conspecifics because of early access to profitable feeding territories [20,21,22,23]. This benefit may be offset by costs such as increased predator exposure [24]. These conflicting selective pressures are believed to play an important role in maintaining variability in larval developmental rate in the wild [22]

Methods

Results

Conclusion