The shortjaw cisco. (Photo credit- Mike Hoff)

Chuck Bronte, fishery biologist at the Green Bay Fish and Wildlife Conservation Office, attended the 10th International symposium on Coregonid Fishes (whitefishes and ciscoes) in Winnipeg, Manitoba, Canada during August 24-28, 2008.  He presented a paper on a new hypothesis for the decline of the shortjaw cisco in Lake Superior. Recent reviews have further documented the decline of shortjaw cisco in Lake Superior.  This fish was the most abundant deepwater cisco in Lake Superior in the early substantial but presently makes up less than 10 percent of all deepwater ciscoes captured in biological surveys.  Directed overfishing of deepwater ciscoes during the substantial and again during the mid-1960s and substantial has been suggested as cause of the demise of the short jaw cisco.  In this paper Bronte, along with USGS and Michigan DNR biologists, re-examined the overfishing hypothesis by using historical and recent survey data to partition out the portion of the historical commercial fishery landings that were shortjaw cisco.  They developed time series of harvest and relative abundance for all statistical districts in Michigan waters of Lake Superior from 1929-1996 , where catch and effort data were available but not previously examined, and looked at the spatial distribution of the fishery and relation of catch to effort for evidence of overfishing. Their analysis suggested that directed overfishing on shortjaw cisco was likely not the cause for the decline of this fish, which appeared to be declining in all statistical districts regardless of the intensity of the fishery.  They propose an alternative hypothesis based on the decline of the keystone predator, the lake trout that released predation pressure on the principal prey, the cisco, which led to their population expansion.  Competitive interactions among cisco and their next nearest bathymetric neighbor, the shortjaw cisco, may be a more likely explanation for their demise.  This led to a loss in the diversity and stability of deepwater ciscoes and further demonstrates the need to maintain top predators and their function in the fish community.  Shortjaw cisco are being considered for listing under the Endangered Species Act.  The paper will be part of the Coregonid Symposium 2008 proceedings, which Bronte will serve as guest editor.