Disentangling individual- and population-scale processes within a latitudinal size-gradient in Sockeye Salmon

Date

2015

Authors

Freshwater, Cameron
Trudel, Marc
Beacham, Terry
Godbout, Lyse
Neville, Chrys-Ellen
Tucker, Strahan
Juanes, Francis

Journal Title

Journal ISSN

Volume Title

Publisher

Canadian Journal of Fisheries and Aquatic Sciences

Abstract

We examined how individual processes contribute to a latitudinal gradient in body size within populations of migrating juvenile Sockeye Salmon (Oncorhynchus nerka) while simultaneously testing for size-selective mortality, a potentially confounding population scale process. Using otolith microstructure techniques and structural equation modeling, we determined that ocean entry size and phenology had strong, direct effects on size at capture. Population identity and freshwater age also had strong indirect effects, moderated by size at entry. Conversely, marine growth rates immediately after entry or before capture were relatively weak predictors of size during migration. We next tested for shifts in size distribution indicative of selective mortality, but detected no evidence of smaller individuals experiencing lower survival during early marine migrations. These results indicate that the migratory distributions of juvenile Sockeye Salmon are influenced by body size and that this variation is predominantly driven by traits present prior to freshwater outmigration, rather than marine growth or differential survival. We suggest integrating individual variation in migratory characteristics with the effects of environmental conditions experienced en route to provide an improved understanding of migratory species.

Description

Keywords

body size, migration, structural equation modelling

Citation

Freshwater, C., Trudel, M., Beacham, T., Godbout, L., Neville, C.-E., Tucker, S., & Juanes, F. (2015). Disentangling individual- and population-scale processes within a latitudinal size-gradient in Sockeye Salmon. Canadian Journal of Fisheries and Aquatic Sciences, 73. https://doi.org/10.1139/cjfas-2015-0344