History of the shortjaw cisco (Coregonus zenithicus) in Lake Superior, 1895-2003

摘要

The shortjaw cisco (Coregonus zenithicus) was once common in Lakes Huron, Michigan, and Superior, but in the 20"' century populations were extirpated in Lakes Huron and Michigan and greatly reduced in Lake Superior largely as a result of overharvest. Using available data, we reconstructed the history of the distribution and abundance of shortjaw cisco in Lake Superior from 1895 through 2003. During the first period (1X95-1908), shortjaw ciscoes were subjected to intense harvest (576 metric tons/yr). Stocks recovered in the second period (1909-1925) under light harvest (55 tons/yr). During this period, a lake-wide survey showed shortjaw cisco to be the dominant chub species, representing >90% of the catch in every region. The third period (1926-1954) started with the resumption of the chub fishery. Harvest declined in the following decades, resulting in an intermediate harvest for the period (221 tons/yr). A 1953 survey of Lake Superior showed shortjaw cisco to be the predominant chub species, but with reduced abundance, and the bloater (Coregonus hoyi) was now dominant or co-dominant in some areas. The fourth period (1955-1987) was marked by high levels of prolonged harvest (617 tons/yr). Assessments during this period showed a sharp decline in abundance of shortjaw cisco, which reached near-zero levels by the mid-1960s to late-1970s. By 1988 the commercial chub harvest declined to low levels and has since remained <50 tons annually, Assessments conducted during L999-2004 showed low densities of shortjaw cisco in eastern Lake Superior and only a few specimens from the western half of the lake. Information gaps in understanding life history attributes, ecology, recruitment dynamics, mortality, and stock structure remain as obstacles to formulating recovery actions.