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COSEWIC assessment and update status report on the Chiselmouth in Canada

Special Significance of the Species

Chiselmouth are endemic to western Canada and the Pacific Northwest United States, and are the only extant species in their genus. The species is not at risk globally. Chiselmouth are morphologically and ecologically unique in Canada because they are the only western species exclusively adapted to herbivory as adults. They are ecologically unique from eastern herbivorous cyprinids (e.g. Campostoma) because of their much larger size and unique chisel-like lower lip and foraging mode. Chiselmouth play a unique ecological role in the streams where they occur (i.e. benthic herbivore), although there are other fishes (e.g. largescale sucker, bridgelip sucker) that may perform similar roles, although this is somewhat speculative as well. It is unclear whether chiselmouth have a keystone effect on nutrient cycling or trophic interactions where they are present (e.g. reduction in benthic algal and invertebrate biomass).

Canadian populations of chiselmouth near the periphery of the species range (e.g. Fraser drainage) are likely to be somewhat ecologically and genetically distinct from populations in the southern (U.S.) part of their distribution. The disjunct distribution of chiselmouth (particularly the more isolated northern Fraser drainage populations) suggests that the smaller lower-density northern populations are likely to be both genetically and ecologically unique and more vulnerable to human impacts or stochastic natural disturbances.

The public are on the whole not familiar with chiselmouth, since it is not a game species subject to harvest, so that there is no strong support or opposition to protecting this species.

The closest species to chiselmouth in appearance are northern pikeminnow and peamouth chub. Since all three species are considered coarsefish and often disparaged or killed by unappreciative anglers, public education to appraise anglers of the unique and fascinating biology of this species would be useful.