The distribution and abundance of deepwater ciscoes in Canadian waters of Lake Superior
Pratt, Thomas C.
Deepwater ciscoes have declined precipitously in the Laurentian Great Lakes, and only Lake Superior contains a fauna resembling that of the early 20th century. The discovery of areas of high abundance and the identification of habitat preferences in Lake Superior would provide important information for the basin-wide recovery of these species. This research completed the most comprehensive deepwater cisco survey in the nearshore Canadian waters of Lake Superior to (1) determine and compare the current distribution and relative abundance of ciscoes, (2) compare coregonid abundance and community structure at specific sites to historic data, and (3) assess habitat preferences of Lake Superior ciscoes. Deepwater ciscoes remain the dominant prey fishes in Lake Superior, and all four species—Coregonus artedi, C. hoyi, C. kiyi and C. zenithicus—remain widely distributed. In general, embayment areas contain the highest densities of all species except C. kiyi, which are found offshore, and there are lower densities in the eastern part of the lake. There have been tremendous changes in the cisco community since the historic surveys, with the formerly dominant C. zenithicus being replaced by C. artedi and C. hoyi. Spatial segregation primarily occurred with depth; C. kiyi is most abundant in deep water (>130 m), C. hoyi and C. zenithicus are most abundant at mid-depths (80–110 m), while C. artedi is most abundant at depths of <60 m.