The main reasons for its extinction was a combination of competition from the invasive alewife, predation by the introduced sea lamprey, and commercial fishing on the Great Lakes.
Commercial fishing in 1930s
Part of the reason for the lack of information on this species could be attributed to the commercial fishing during the early 1930s, before deep water species were properly analysed. The deepwater cisco was abundant before the 1900s as, before large-scale commercial fishing commenced in Lake Michigan, the larger ciscoes had no natural predators.
It was not until the 1930s that the species was subject to commercial fishing exploitation. The deepwater cisco, also known as chubs in fishing terms, was prized for its larger-than-normal size. During this exploitation, the numbers of this species declined dramatically.
The last deepwater cisco specimens were recorded in Lake Michigan in 1951 and Lake Huron in 1952. The species was declared extinct shortly after. When a re-evaluation was conducted in several states bordering Lake Michigan in the 1960s, there were no identifiable specimens of the deepwater cisco in any of the samplings. This served to confirm its extinction, caused by a combination of commercial fishing and invasive predators such as the sea lamprey.
Additional field notes
Deepwater cisco are an extinct Great Lakes fish with a long, narrow snout.
Sources: Coregonus johannae species summary
Appearance of a lost species
FishBase describes a relatively long head on an elongated, moderately compressed body. The mouth is terminal, although the lower jaw can be shorter than, equal to, or longer than the upper one. Silvery coloration can show pink iridescence, with pale blue or green above and mostly translucent fins. These details concern the historical species, rather than a fish that can still be sought in its former lakes.
Sources: Coregonus johannae species summary
Article text: Wikipedia contributors, Deepwater cisco (source revision). Licensed under CC BY-SA 4.0. Retrieved 2026-10-11.
