Research Document - 2013/106
Variation in morphology, life history and ecology of cisco in Great Bear Lake, Northwest Territories, Canada
By K. Howland, C. Gallagher, D. Boguski, L. Chavarie, J. Reist, B. Rosenburg, and S. Wiley
Abstract
Historical reports indicate that more than one form of cisco may occur in Great Bear Lake ̶ Coregonus artedi and possibly C. sardinella. More recent depth-stratified sampling of cisco concurs with earlier studies and includes what may be two or more forms or species. Based on preliminary results, cisco captured in deeper waters of Great Bear Lake showed characteristics that are consistent with those described for Shortjaw Cisco (C. zenithicus) including shorter, fewer and more widely spaced gillrakers, lighter paired fins and a diet consisting mainly of Mysis diluviana. Other characteristics such as longer paired fins and greater body depth were not consistent with C. zenithicus, but are often associated with adaptations to vertically migrating in deeper water and have been noted in other deepwater coregonids such as Coregonus kiyi. Cisco from shallow habitats had characteristics typical of C. artedi including a more streamlined body, moderately pigmented paired fins, longer more numerous gillrakers and a diet dominated by smaller zooplankton. Deep- and shallow-water cisco were also found to differ in their life history traits, with the deep-water cisco being smaller, later maturing and slower growing than their shallow-water counterparts. In addition to variation by depth, we also observed consistent variation among geographically separated populations within deep- and shallow-water types that may, in part, be due to phenotypic plasticity of morphological traits in response to other habitat differences among lake areas. With the exception of Great Bear Lake, C. zenithicus or a C. zenthicus-like form of cisco has been reported from most of the remnant proglacial Great Lakes in North America running from the Laurentian Great Lakes northwest to Great Slave Lake. Thus our findings may represent a northern range extension for this particular form or species and certainly represents the first comprehensive account of distinct cisco ecotypes within Great Bear Lake.
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