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

Abstract

AbstractAnadromous 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.