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Abstract
The diversity and abundance of ciscoes has declined in the Great Lakes, with only Lake Superior retaining its original Cisco fauna; yet as a group, ciscoes remain poorly studied. We examined age and growth, sex ratios, and estimated survivorship and mortality of deepwater ciscoes (Bloater: Coregonus hoyi, Kiyi: C. kiyi, and Shortjaw Cisco: C. zenithicus) and Cisco C. artedi. All fish were captured in gill nets set >60 m in Canadian waters of Lake Superior from 2007–2009. Survivorship was higher than expected, with total annual survival rates ranging from 0.615 (Kiyi) to 0.785 (Shortjaw Cisco). This result was attributed to using otoliths to estimate ages rather than scales as done in previous investigations. Maximum ages of ciscoes exceeded 20 years with Cisco, the largest, longest-lived species, followed by Shortjaw Cisco, Bloater and Kiyi. Females dominated adult populations in all species; females were larger-at-age and had greater longevity, resulting in sex ratios skewed heavily towards females. With the exception of age and growth data, the life history characteristics that we observed were consistent with historic data from the early part of the 20th century.
Acknowledgements
Our work was funded by the Canada-Ontario Agreement Respecting the Great Lakes Basin Ecosystem (COA) and DFO Species at Risk Program (SARCEP). We thank Lisa O’Connor, Bill Gardner, John Deeg, Jon Chicoine, Dave Montgomery, Cheryl Widdifield, Grant Fortin, Janice McKee and Kim Caldwell for all their efforts in the field and in the laboratory. Owen Gorman and two anonymous reviewers provided helpful criticisms of an earlier draft of the article.