Shortnose cisco (Coregonus reighardi) COSEWIC assessment and status report: chapter 3

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Species Information

Name and classification

The shortnose cisco (Coregonus reighardi Koelz) was originally described from lakes Huron, Michigan, Nipigon, Ontario and Superior (Koelz 1929). However, a form of this species, C. reighardi dymondi, described from lakes Nipigon and Superior by Koelz (1929) was more recently found to be a synonym of the shortjaw cisco (C. zenthicus) (Todd and Smith 1980). The shortnose cisco was one of 10 cisco species found in Canada (Scott and Crossman 1998), one of seven cisco species found in the Great Lakes (Cudmore-Vokey and Crossman 2000), and one of six cisco species identified as an incipient species flock ‘endemic’ to the Great Lakes by Koelz (1929). These counts exclude the longjaw cisco (C. alpenae), described by Koelz (1929) and included in Scott and Crossman (1998), as a synonym of the shortjaw cisco (C. zenithicus) by Todd et al. (1981). Two (C. nigripinnis, C. zenithicus) of the six valid species, originally identified as “endemic” to the Great Lakes by Koelz (1929), may occur outside of the Great Lakes basin (Lee et al. 1980, Mandrak and Crossman 1992).

Webb and Todd (1995) raised the possibility that the shortnose cisco populations in each of the Great Lakes may not share a recent, common ancestor, and that each population might be a separate evolutionary entity. However, they did not provide any evidence to support, or refute, this hypothesis.

Research on the shortjaw cisco (C. zenithicus), originally believed to be endemic to the Great Lakes, revealed that Great Lakes and inland populations of this species were genetically indistinguishable from the cisco (C. artedi); however, the shortjaw cisco is still considered to be a valid species (Todd et al. 1981, Turgeon et al. 1999, Turgeon and Bernatchez 2003). This may be an indication that some, or all, of the endemic cisco species may actually be ecomorphotypes of the cisco (C. artedi), rather than valid species. If, in future, this was shown to be true for the shortnose cisco, the shortnose cisco would still be considered an evolutionarily significant unit (ESU) or, at the very least, a unique morphotype. To date, a taxonomic revision of the endemic ciscoes has not been undertaken; therefore, the endemic species should be considered valid.

Description

The shortnose cisco was a member of the subfamily Coregoninae of the family Salmonidae (Nelson et al. 2004) (Figure 1). It is characterized by a short head (20-23% of total length), small eye (22.2-26.4% of head length), short snout (truncate in side view because of near vertical position of premaxillaries), small terminal mouth, lower jaw included in upper jaw, and gill raker count of 32-42 (Scott and Crossman 1998). Nuptial tubercles are present on mature males and, at least some, females (Scott and Crossman 1998). The shortnose cisco can be distinguished from the other cisco species found in the Great Lakes by the distinctive dark pigmentation of the snout (premaxillaries, maxillaries and lower jaw) (Scott and Crossman 1998).

Figure 1. Shortnose cisco, Coregonus reighardi.  From Koelz (1929).

Designatable units

All Canadian populations were found within the Great Lakes-Western St. Lawrence ecozone of the freshwater ecozone classification adopted by COSEWIC (COSEWIC 2003). As a result of its absence from Lake Erie, the Lake Ontario population was likely distinct from the population(s) in the upper Great Lakes. The population structure of shortnose cisco within lakes Huron and Michigan is unknown.