Lake Ontario and Great Lakes kiyi COSEWIC assessment and status report: chapter 7

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Population Sizes and Trends

Although the deepwater cisco fishery (commonly known as the “chub fishery”) was very important in the Great Lakes, the catches were rarely identified to species (Lawrie and Rahrer 1973). Too few collections of kiyi (recorded to species) have been documented over time in a standardized manner to evaluate population sizes and trends.

In Lake Ontario, kiyi made up 52.8% of all ciscoes (n=395) caught in experimental gill nets in 1927 (Pritchard 1931). This number fell to 0.01% (n=899) in 1942 (Stone 1947), and only a single individual (n=15) was captured in 1964, the last year that it was recorded in Lake Ontario (Wells 1969). Subsequent index sampling by OMNR, commercial cisco fishing, and sampling of historic sites in western Lake Ontario in 2002 (N.E. Mandrak, unpubl. data), failed to capture any specimens.

Although there is virtually no historic information on the population size of kiyi (identified to species) for Lake Superior (Lawrie and Rahrer 1973, Selgeby et al. 1994), there are good recent data for Lake Superior (Petzold 2002). Gillnet and trawling surveys of eastern Lake Superior in 2000-01 indicated that kiyi comprised anywhere between 1% and 15% of the chub catch, and there were an estimated 2,211 tonnes (271-4,452 tonnes; 90% CI) of chub in depths greater than 105m, the preferred depths of kiyi. Based on these estimates, there were between 22 and 330 tonnes of kiyi in the deepest parts of the Canadian waters of eastern Lake Superior in 2000-01 (Petzold 2002), which represents approximately 25% of the total Canadian habitat. Based on an average weight of 170 g. (Scott and Crossman 1998) this would equate to approximately 129,412 to 2,000,000 fish in the eastern (Canadian) waters of the lake or an overall range of 500,000 to 8,000,000 fish in the Canadian waters of the lake. Data from 2003 indicated that Kiyi were the second most abundant prey species in Lake Superior and outnumber bloater (Coregonus hoyi) in many locations (K. Cullis, pers. comm.).

No historic data, summarized by cisco species, exist for the Canadian waters of Lake Huron. An examination of 1,943 ciscoes, collected at 46 deepwater locations in Lake Huron in 2002 and 2003, failed to find any kiyi (N.E. Mandrak, unpubl. data).

Although it is possible that populations in lakes Huron and Michigan could be restablished due to a rescue effect from Lake Superior populations, there is no evidence that this has occurred in the 30 years since the kiyi was last recorded in these lakes however, larvae could be flushed through the St. Mary’s River.