The role of body size versus growth on the decision to migrate: a case study with Salmo trutta |
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Authors: | Acolas M L Labonne J Baglinière J L Roussel J M |
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Institution: | (1) INRA, UMR INRA-Agrocampus-Ouest Ecologie et Sant? des Ecosyst?mes, 65 rue de Saint-Brieuc, 35042 Rennes, France;(2) INRA, UMR ECOBIOP, 64310 St-P?e Sur Nivelle, France |
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Abstract: | In a population exhibiting partial migration (i.e. migration and residency tactics occur in the same population), the mechanisms
underlying the tactical choice are still unclear. Empirical studies have highlighted a variety of factors that could influence
the coexistence of resident and migratory individuals, with growth and body size considered to be key factors in the decision
to migrate. Most studies suffer from at least one of the two following caveats: (1) survival and capture probabilities are
not taken into account in the data analysis, and (2) body size is often used as a proxy for individual growth. We performed
a capture–mark–recapture experiment to study partial migration among juvenile brown trout Salmo trutta at the end of their first year, when a portion of the population emigrate from the natal stream while others choose residency
tactic. Bayesian multistate capture–recapture models accounting for survival and recaptures probabilities were used to investigate
the relative role of body size and individual growth on survival and migration probabilities. Our results show that, despite
an apparent effect of both size and growth on migration, growth is the better integrative parameter and acts directly on migration
probability whereas body size acts more strongly on survival. Consequently, we recommend caution if size is used as a proxy
for growth when studying the factors that drive partial migration in juvenile salmonid species. |
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