Freshwater early life growth influences partial migration in populations of Dolly Varden (Salvelinus malma malma)

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.

Life history differences between 2 anadromous populations of the northern form of the Dolly Varden (Salvelinus malma malma) in Bristol Bay in southwestern Alaska

“…These length and age values are comparable to those for conspecifics at similar latitudes (Maekawa and Nakano, 2002), although older individuals occur in Arctic populations (Stolarski and Sutton, 2013;Gallagher et al, 2016). Morrison et al (2021) reported that rapid growth in fresh water was associated with early age at first migration in Dolly Varden and that growth rate in fresh water is typically inversely related to smolt age in salmonids (McCormick et al, 1998;. In contrast to the modest differences in size and age between the populations on opposite sides of Bristol Bay, a clear difference in age at migration was observed.…”

“…Similarly, a population of the southern subspecies of Dolly Varden along the southern Alaska Peninsula also migrated to sea at a younger age, although at a smaller body size at that age of migration . Dolly Varden at the northern end of their range also smolt at a younger age than the fish sampled from the Nushagak District ( Morrison et al, 2021).…”

“…The Dolly Varden (S. malma) is an iteroparous char species of the North Pacific Rim with 3 subspecies (Taylor and May-McNally, 2015), and there are fluvial (Denton et al, 2010;Ayer et al, 2018), adfluvial (Markevich et al, 2018), and anadromous or partially anadromous populations of this species (Bond and Quinn, 2013;Morrison et al, 2021). Anadromy is known for the 2 North American subspecies or forms in Alaska.…”

Monsoonal wet season influences the migration tendency of a catadromous fish (barramundi Lates calcarifer)

“…For example, numerous studies have demonstrated the importance of juvenile growth rate on migration propensity (e.g. Kraus & Secor, 2004; Morrison et al., 2021), or how migration can itself lead to increased juvenile growth (Barrow et al., 2021). In some scenarios, growth rate and/or larger body size is positively correlated with migration probability, which is generally assumed to reflect a threshold size which must be attained by individuals to meet energetic demands necessary for migration (Chapman et al., 2012).…”