Abstract
Populations of northern Dolly Varden (Salvelinus malma malma) exhibit partial seaward migration, yet little is known about this phenomenon in Dolly Varden populations. Our study analyzed data from three different Dolly Varden populations in the western Canadian Arctic in order to determine if: (1) differences in size-at-first seaward migration exist between fish that migrate at early and late ages among populations inhabiting different river systems, and (2) annual growth influences anadromous or resident life history choice. Otolith strontium analysis and back-calculation were used to determine age- and size-at-first seaward migration, respectively. Differences in age- and size-at-first seaward migration were determined across river system and migration age. Back-calculated fish lengths were compared using a mixed effect model to determine how early growth influences migratory tactics (early or late aged smolt, or resident). Our results indicate that fish exhibiting faster early growth migrated in earlier years and at smaller sizes than slower growing fish, however size- and age-at first seaward migration varied by river system. Faster growing Dolly Varden tended to become either residents or early smolts, while slower growth was associated with smolting later in life. This is contrary to life history theory where the fastest growing fish in a population should mature as a resident. Our results indicate factors other than growth may be influencing life history ‘decisions’ in Dolly Varden. Future work on growth efficiencies and metabolic rates is needed to assess how they affect migratory behaviours.
Highlights
Migration in salmonids is a well-studied phenomenon with the type and extent of migration varying among species and populations
Our study demonstrated that growth in early life influenced migration tactics of Dolly Varden
Results showed that there was a difference in size-at-first seaward migration between Dolly Varden that migrated as early smolts and those that migrated as late smolts, with early smolts migrating at smaller sizes compared to late smolts
Summary
Migration in salmonids is a well-studied phenomenon with the type and extent of migration varying among species and populations. Partial migration (or partial anadromy) occurs when a proportion of the population migrates to more. Howland, and are both considered last authors for this publication. Polar Biology (2021) 44:1353–1364 the size, condition, and behavior of other males with whom they must compete (Hendry et al 2004). While larger males are able to maintain a dominant position close to gravid females, and fight off competing males (Fleming and Gross 1994), precocious males that adopt a “sneak spawn” strategy can fertilize a substantial portion of eggs (Theriault et al 2007) making migration potentially less beneficial to male salmonids. Anadromous individuals often delay maturity, but benefit from an increased rate of growth, larger size at maturity, and increased reproductive output (Gross 1987; Hendry et al 2004). Disadvantages to anadromous behaviour include energy expenditure for migration and osmoregulation, and increased risk of predation during migration and in marine environments
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