COSEWIC Assessment and Update Status Report on the Bering Cisco in Canada
- Assessment Summary
- Executive Summary
- COSEWIC History, Mandate, Membership and Definitions
- Lists of Figures and Tables
- Species Information
- Population Sizes and Trends
- Limiting Factors and Threats
- Special Significance of the Species
- Existing Protection or Other Status
- Technical Summary
- Acknowledgements and Information Sources
- Biographical Summary of Report Writer and Authorities Contacted and Personal Communications
The Bering cisco is troutlike, having an elongate silvery body and terminal jaws. Adults may attain fork lengths of up to 48 cm; however, the average (fork) length of migrating fish in the Yukon River is about 37 cm. The species is distinguished from other cisco by the pale, almost colourless pelvic and pectoral fins and 18 to 25 gill rakers on the lower portion of the first gill arch. The Bering cisco is presumably anadromous, with extensive spawning migrations into the upper reaches of large rivers that flow into the Beaufort, Bering and Chukchi seas.
In North America, Bering cisco are more commonly encountered in coastal regions of Alaska in the Beaufort, Bering and Chukchi seas. Spawning migrations are almost exclusively limited to Alaska, although some migrants in the Yukon River reach Canadian waters with sporadic observations as far upstream as Dawson City, Yukon Territory. It is conceivable that the species may be found along the Yukon Territory portion of the Beaufort Sea coastline, but its presence there has not been confirmed.
The Bering cisco is typically found in nearshore coastal habitat of low salinity. It is thought to be less tolerant of the higher saline waters that occur offshore in marine environments. The species prefers river estuaries and brackish water lagoons along coastal Alaska, where they feed on a variety of benthic and planktonic foods. Large annual migrations are made to spawning locations in the mainstem portions of large rivers of Alaska.
The biology of the Bering cisco has received little study in Canada. In Alaska, the life history of Bering cisco is thought to be analogous to Arctic cisco of the Mackenzie River. Fish apparently winter in brackish water near river mouths. Anadromous populations of Bering cisco are thought to have migrations of over 2100 km in the Yukon River. Spawning occurs over loosely compacted gravel beds in swiftly flowing water. Eggs are typically broadcast and abandoned by their parents. After spawning, adults are believed to move downstream to the sea. It is unknown if adults are repeat spawners. The eggs presumably hatch in the spring and the young descend downstream to brackish estuarine habitat. Bering cisco are a schooling species that rear and feed in coastal waters before reaching sexual maturity. Sexual maturity is thought to be attained at 4 to 9 years of age. There is potential for some segment of the annual migration to possibly winter in freshwater.
Population Sizes and Trends
There has been very little research, assessment or management effort focused on the Bering cisco throughout their range. Correspondence with management biologists and a literature search revealed little information specific to population size, catch or abundance. The majority of information related to this species is simply reports of their occurrence in a particular region, usually through fisheries investigations on other salmonid species.
Limiting Factors and Threats
The migratory behaviour of Bering cisco makes the species susceptible to obstructions such as causeways and dams. The reduction of water flow or alteration in discharge or water quality, in those rivers where they are known to spawn, could be a limiting factor and threat in the future. Present subsistence harvests are thought to be relatively small and conservative throughout their range, but species-specific harvest data are not available. It is possible that commercial fisheries for other species could threaten the Bering cisco.
Special Significance of the Species
In Alaska, large spawning movements in the Yukon River suggest Bering cisco play a significant role in the ecology of the Bering Sea. The species is presumably an important food source to a number of predators in coastal environments. In Canada, their occurrence may represent a population(s) on the farthest edge of its migratory range. The species is utilized in subsistence fisheries throughout its coastal range, although harvests are thought to be conservative relative to salmon.
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