Juvenile migration in brown trout: a consequence of energetic state

Abstract

Summary 0[ We explored the mechanisms determining age and size at juvenile migration in brown trout Salmo trutta L[ A 022 Cs tracer methodology was used to estimate food consumption of juvenile brown trout in a Norwegian stream\ and the energy budgets of early migrants and stream residents were compared[ 1[ Fast!growing brown trout migrated to the lake earlier and at a smaller body size than slower!growing individuals[ The 1¦ migrants were signi_cantly larger than those that remained 0 or more years longer in the stream[ The 2¦ migrants were signi_cantly larger than the 1¦ migrants[ Some fast!growing males matured in the stream\ whereas all females left the stream before maturing sexually[ 2[ The food consumption and the energy budgets for 1¦ migrants were more than four times higher than those of the resident 1¦ _sh[ Total energy allocated to growth was also higher among migrants\ and the total metabolic costs were _ve times higher among migrants than among resident _sh[ 3[ The proportional energy allocation to growth among the 1¦ migrants was much lower "about half# than that of those remaining longer in the stream[ The reduction in the proportion of energy available for growth from age 0¦ to 1¦ was larger among migrants "77)# than among resident _sh "57)#[ Reduction in the proportion of energy available for growth is a probable explanation for why migrations are initiated at age 1[ 4[ Our study supports the hypothesis that fast!growing individuals shift their niche earlier and at a smaller body size than slower!growing individuals because they maintain higher metabolic rates and are energetically constrained at a younger age by limited food resources than slow growers[ Key!words] energy budget\ food consumption\ growth\ life history\ metabolic rate[ Journal of Animal Ecology "0888# 57\ 672Ð682

Adaptive phenotypic plasticity of eel diadromy

“…Third, glass eels that precociously settle in the estuary are lighter than river colonizers (Edeline et al 2004). These data strongly support the view that glass eels migration is conditional on the fact that individuals have sufficient energy stores with which to migrate, as also observed in juvenile salmonids (Forseth et al 1999, Thériault & Dodson 2003.…”

Marine migrations in anadromous brown trout (Salmo trutta). Fjord residency as a possible alternative in the continuum of migration to the open sea

“…The underlying causes of the present partial migrations are not elucidated by this experiment. However, in the context of a conditional strategy, it is possible that factors related to the energetic status (Forseth et al, 1999), growth and/or metabolic rate (Cucherousset et al, 2005), energy allocation (Jonsson and Jonsson 1998), and inherited components (Giger et al, 2006) might affect the individual's decision to 19/28 migrated. We suggest further studies on the initial marine behaviour of sea trout incorporating measurements on the above mentioned factors to potentially identify proximate causes for the observed behaviour.…”

“…Fulton's K;Fulton 1902) and the individual's energetic reserves may influence the individual's decision towards migration (Forseth et al, 1999, Jonsson and Gravem 1985, Wysujack et al, 2009. In addition, the ratio mortality to growth is believed to be a selective driver in this decision and ultimately be the cause of such migration (e.g.…”

The association between parental life history and offspring phenotype

“…One trait that has received a considerable amount of attention is metabolic rate (Forseth et al, 1999), partly because it is often correlated with dominance or growth (Metcalfe et al, 1995;Álvarez and Nicieza, 2005) and partly because it constitutes the fundamental energy budget of organisms. Standard metabolic rate (SMR, usually measured in terms of oxygen consumption) is the minimal maintenance metabolic rate of an ectotherm in a postabsorptive and inactive state (so is the equivalent of the basal metabolic rate of an endotherm), and is an integrated measure of the energy expenditure involved in tissue maintenance and organism homeostasis.…”

“…Individual differences in SMR within salmon and trout populations have been linked to variation in individual growth and life history strategies (e.g. timing of smolt migration; Metcalfe et al, 1995;Forseth et al, 1999;Finstad et al, 2007). In contrast, the role of AS remains relatively understudied compared with SMR, although it has been found to be correlated with swim performance, distance of migration (Eliason et al, 2011) and survival of individuals in challenging environments Killen et al, 2012).…”