Abstract:
Research conducted on humpback whitefish Coregonus pidschian in the Copper River Delta, Alaska has revealed a complex life history involving seasonal migrations and the occupation of a variety of freshwater and marine habitats including lacustrine, riverine, estuarine, and marine. Forty-five whitefish were tagged with radio transmitters in 2006 and 2007, and another 29 whitefish were tagged with acoustic tags in 2008. In addition, otolith chemistry was used to evaluate marine habitat use of humpback whitefish sampled from McKinley Lake in the Copper River Delta, Alaska. Movements and migration of tagged fish were tracked using biotelemetry techniques from boats, airplanes, and fixed receiver stations throughout the spring, summer, and fall. Sagittal otoliths were extracted from 20 humpback whitefish and a chemical analysis was performed to evaluate levels of Sr:Ca.
Biotelemetry and sampling results revealed seasonal migrations where humpback whitefish migrated into McKinley Lake in mid to late spring and left the lake by late summer and early fall. Fish migrated to the Copper River in the fall by traveling down Alaganik Slough and then to the Copper River by traveling through Pete Dahl Cutoff Slough or the Gulf of Alaska. Fish travel up the Copper River presumably to their spawning grounds. Nine tagged fish returned to McKinley Lake in 2007 and four tagged fish in 2008, indicating some fidelity to the summer feeding site. Otolith chemistry detected marine migrations in 45% of the samples. Three migratory behaviors were observed, while some individuals inhabited only freshwater environments, some individuals made single migrations to marine habitats, and other individuals made multiple migrations to marine habitats. Age of whitefish ranged from 2 to 9 years.
Analysis of small-scale movement of humpback whitefish in McKinley Lake found movement rates to be significantly higher at dusk compared to night in one sampling period. However, diel movement activity in all other diel periods did not significantly differ, suggesting arrhythmic diel movement. A large portion of the lake was occupied at any given time, but not all areas were used equally. Activity levels, measured by change in zones, were variable between dates and indicated that fish often moved between detection zones. An increase in activity was observed in individuals 48 h prior to migration from the lake.
This study provides the first documentation of migration, movement, and habitat use of humpback whitefish in the Copper River Delta, Alaska. Results of this study will help inform management of humpback whitefish in order to sustain populations into the future. This information should be considered in land use and species management planning in the Copper River basin including fish passage and harvest regulations.
