New Insights into the Biology of Anadromous Dolly Varden in the Canning River, Arctic National Wildlife Refuge, Alaska

Abstract

Anadromous Dolly Varden Salvelinus malma in northeastern Alaska migrate to sea during the summer to feed but must overwinter in rivers because the sea under ice becomes too cold for salmonids. Flow ceases in rivers during the winter except for a few perennial springs in which all fish congregate. The Canning River is one of the largest rivers in the area with numerous perennial springs that support Dolly Varden during the winter. It also marks the western boundary of the Arctic National Wildlife Refuge as it flows across the coastal plain to the Beaufort Sea. We sought to improve our understanding of habitat use, migration timing, survival, and interdrainage exchange of Dolly Varden in the Canning River to improve management efforts to minimize the environmental impacts of potential hydrocarbon resource development in the area. To achieve these objectives, we deployed 210 radio tags in mature Dolly Varden during 2014 and 2015 and then determined their seasonal locations with aerial surveys of the Canning River and other nearby rivers and with a radio receiver located in the lower Canning River. Dolly Varden spawned and overwintered in several areas of the main stem and in perennial springs in the upper reaches of the drainage. Nonspawning fish occupied similar main-stem habitats during the winter, but did not migrate into upstream reaches. Migration to sea occurred during a brief period in early to mid-June, while fish returned to the river in small numbers over the next 3 months. The estimated annual survival of nonspawners (0.62) was significantly greater than that for postspawners (0.34). Survival in freshwater during winter was significantly greater than that in marine environments during the summer for both demographic groups. The interdrainage exchange rate was estimated to be 0.37. These data enhance our understanding of annual cycles of Dolly Varden habitat use, migration, and population dynamics.

Migration tactics affect spawning frequency in an iteroparous salmonid (Salvelinus malma) from the Arctic

“…Spawning and overwintering habitat are inextricably linked and occur in alpine headwater reaches in areas associated with perennial ground water springs that maintain unfrozen stretches of river throughout the winter [26]. After rearing in natal streams for 2–5 years, individuals undertake migrations to feed in the sea each spring (usually late June and July) during ice breakup and typically return to freshwater habitats from mid-summer (middle of July) to late-fall (middle of September) to spawn and or overwinter [14,20].…”

“…Similarly, skipping migration for the purpose of spawning has also been documented in northern Dolly Varden ( S . malma malma ) but only in anadromous populations inhabiting river systems in Alaska [18–20]. Alternatively, the majority of Arctic charr from the Island of Spitsbergen (Norway) migrate annually after smoltification (first time to sea) [16].…”

“…It is unknown how the migration distance influences the migration and reproductive characteristics of the population. Unlike Dolly Varden in Arctic Alaska [18–20], little is known about annual seaward migrations in populations further east and almost nothing is known about how migration patterns affect spawning frequency in this species. If Dolly Varden from the Rat River exhibit variation in annual ocean migration patterns we predict differences in spawning frequencies and longevity.…”

Is Dolly Varden in Arctic Alaska Increasing in Length in a Warming Climate?

“…Anadromous Dolly Varden in the Arctic Alaska live in freshwater for 2-5 y before beginning annual migrations between marine waters in the summer to feed and rivers in the autumn through spring to overwinter (Armstrong and Morrow 1980;McCart 1980;DeCicco 1997). It is thought that, similar to anadromous Arctic char, the vast majority of growth of anadromous Dolly Varden occurs in the ocean during the short summer feeding season (McCart 1980;Courtney et al 2018;Brown et al 2019). Dolly Varden usually undertake three to five ocean migrations before reaching maturity (Armstrong and Morrow 1980).…”

“…Dolly Varden usually undertake three to five ocean migrations before reaching maturity (Armstrong and Morrow 1980). Once becoming sexually mature, spawning occurs in the autumn and it is thought that individuals usually spawn biennially (Furniss 1975;DeCicco 1989;Brown et al 2019). Currently, estimates of Dolly Varden catch and harvest on the North Slope suggest a sustainable level of harvest (Scanlon 2018).…”