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
- Nutrition and Interspecific Interactions
The Bering cisco is known for extensive migrations related to spawning (Morrow 1980). The species is one of several anadromous coregonid fish to migrate upstream to spawn in large rivers during spring and summer (Figure 3). Bering cisco are thought to be anadromous with no freshwater non-migratory forms (Brown, pers. comm., 2003). Upon completion of spawning, spent fish migrate downstream to overwinter beneath the ice in coastal river deltas and estuaries. Feeding is thought to occur in coastal areas especially near river mouths and brackish lagoons (McPhail and Lindsey 1970). Rearing and sexual maturation of juveniles occurs within coastal waters. The species is widely dispersed over a large geographical range along the Alaskan coastline. The cyclic pattern of migrations between the river and ocean occurs annually. The extent of fidelity to specific spawning areas by the species is unknown.
Sexually mature Bering cisco sampled in fishwheels located in the Yukon River approximately 1200 river km from the sea in Alaska were between 31 and 45 cm in fork length and were 4 to 9 years in age (Brown, pers. comm., 2003). Alt (1973) reported that the species reaches maturity at 4 years of age and may live to 7 years or older. Male fish averaged slightly smaller in size than females and were of a younger age. Spawning is thought to occur over loosely compacted gravel beds in swiftly flowing water. A known spawning area on the Yukon River in Alaska is within a 120 km section of highly braided river (Figure 4). Eggs are typically broadcast and abandoned, after which spent adults presumably move downstream to the sea. The eggs hatch in the spring and the young descend downstream to brackish estuarine habitat to rear.
Very little is known about survival and mortality rates for this species. The Bering cisco is likely an important food source for predacious fish, especially along the coastal rearing and overwintering areas. The extent of utilization by avian and mammalian predators is unknown. Bering cisco are harvested along with other salmonids in subsistence fisheries throughout the range (R. Nagano, Lands and Resource Development, Dawson City, Yukon, personal communication 2004).
There is no information on established physiological preferences of Bering cisco. Research conducted on Arctic cisco, a closely related species with presumed similar physiology, shows avoidance of cold highly saline marine environments, with growth directly related to water temperatures (Griffiths et al. 1992; Fechhelm et al. 1993). The premise that both species utilize similar coastal habitat suggests a similar physiological preference for seasonally warmer, brackish nearshore waters. They can tolerate salinity of 27-31%, and some may overwinter in the Yukon River drainage (Alt 1973).
Spawning runs begin in late May to early June near river mouths. Catch data from Alaskan fishwheels situated in the Yukon River approximately 1200 river km from the sea indicate two distinct migratory peaks. The first, during late June, is followed by another in late August and into September. The later peak appears to coincide with more extensive migratory travel and is thought to contain a segment of the population that is bound for Canadian waters. In Alaskan fishwheels, up to 200 Bering cisco are enumerated each day during migratory peaks (Brown, pers. comm., 2003).
Migrating Bering cisco are also occasionally captured in Canadian fishwheels situated near the United States/Canada border, located 2100 river km from the sea. The run is more prevalent in some years than others (Milligan, pers. comm., 2003). Observations of less than 100 fish each year are reported as an incidental catch in two fish wheels used by Fisheries and Oceans Canada to capture and mark migrating fall chum salmon (Oncorhynchus keta).
This program has been conducted since 1982. Since the Bering cisco are captured in the fall of the year, September to mid-October, it has been assumed they are undertaking a spawning migration; however, spawning locations within Canadian sections of the Yukon River have not been identified (Milligan, pers. comm., 2003).
After spawning, adults are thought to move downstream to the sea. The eggs presumably hatch in the spring and the young descend downstream to brackish estuarine habitat where they are partially dispersed by prevailing currents and winds. Rearing and sexual maturation occur along coastal waters of Alaska over a large geographical region. The only drainages in Alaska known to contain spawning runs are the Kuskokwim and Yukon rivers (Brown, pers. com., 2003).
They are thought to feed on invertebrates (probably amphipods) and other small fish (McPhail and Lindsey 1970; Alt 1973). Feeding is thought to occur primarily in the productive and food-rich nearshore coastal waters containing a diversity of invertebrates and cottid fishes (Lee et al. 1980; Morrow 1980). Bering cisco are not known to feed during their spawning migrations up the Yukon River. There currently is no information on nutrition requirements or interspecific interactions for either freshwater or coastal environments.
Bering cisco are known for migrating great distances. Migrating fish require access to large swift-flowing rivers to reproduce. While migratory behaviour in freshwater streams and rivers can generally increase a species’ vulnerability to natural disturbances, the use of spawning habitat associated with the mainstem of large rivers is perhaps a strategy that minimizes these risks. Disturbances such as slumping permafrost, forest fires, extreme precipitation events or drought, temperature fluctuations and natural obstructions such as beaver dams or landslides have a more pronounced effect on smaller streams. The tolerance of Bering cisco to environmental degradation is unknown. The species has never been reared for use in aquaculture.
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