The total ruffe catch (2,345), from Thunder Bay Harbour, Lake Superior, during the Ruffe Population Investigation, in the Fall of 2006. - FWS photo

This ruffe with sunfish morphology, was captured in Thunder Bay Harbour, Ontario, Lake Superior, in October 2006. - FWS photo

The Ashland Fishery Resources Office and the Upper Great Lakes Management Unit of the Ontario Ministry of Natural Resources (OMNR) completed a fall investigation of the invasive ruffe population in central and southern Thunder Bay Harbour, Lake Superior. 

This long term investigation is conducted annually to monitor relative abundance and distribution of ruffe and native fish in central and southern Thunder Bay Harbour. 

A total of 2,345 ruffe were captured for a catch-per-unit-effort (CPUE) of 1,655 ruffe per hour in trawls.  This catch is more than double the previous high catch, and the CPUE is triple the previous high CPUE set in 2003. 

In the southern half of the harbour, the largest ruffe colonies occur in the Kaministiquia and Mission Rivers which drain into the harbour.  Stickleback, smelt, and trout-perch have been the most abundant native fish in association with ruffe since this survey began in 1991.  

As ruffe increase in abundance, data from this investigation may reveal potential impact on native species in terms of abundance, and these investigations also aid in detecting ruffe vulnerabilities that may be exploited for population reductions. 

A potential ruffe vulnerability was detected in the Kaministiquia River, and the feasibility of an effective population reduction there is pending investigation.