Sustainability of the Lake Superior Fish Community: Interactions in a Food Web Context |
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Authors: | James F Kitchell Sean P Cox Chris J Harvey Timothy B Johnson Doran M Mason Kurt K Schoen Kerim Aydin Charles Bronte Mark Ebener Michael Hansen Michael Hoff Steve Schram Don Schreiner Carl J Walters |
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Institution: | (1) Center for Limnology, 680 N. Park Street, University of Wisconsin–Madison, Madison, Wisconsin, 53706 USA , US;(2) School of Fisheries, University of Washington, Seattle, Washington, USA, US;(3) United States Geological Survey, Great Lakes Science Center, Lake Superior Biological Station, Ashland, Wisconsin, USA, US;(4) Chippewa–Ottawa Treaty Fishery Management Authority, Sault Ste. Marie, Michigan, USA, US;(5) College of Natural Resources, University of Wisconsin–Stevens Point, Stevens Point, Wisconsin, USA, US;(6) Wisconsin Department of Natural Resources, Bayfield, Wisconsin, USA, US;(7) Minnesota Department of Natural Resources, Duluth, Minnesota, USA, US;(8) Fisheries Centre, University of British Columbia, Vancouver, British Columbia, Canada, CA |
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Abstract: | The restoration and rehabilitation of the native fish communities is a long-term goal for the Laurentian Great Lakes. In Lake
Superior, the ongoing restoration of the native lake trout populations is now regarded as one of the major success stories
in fisheries management. However, populations of the deepwater morphotype (siscowet lake trout) have increased much more substantially
than those of the nearshore morphotype (lean lake trout), and the ecosystem now contains an assemblage of exotic species such
as sea lamprey, rainbow smelt, and Pacific salmon (chinook, coho, and steelhead). Those species play an important role in
defining the constraints and opportunities for ecosystem management. We combined an equilibrium mass balance model (Ecopath)
with a dynamic food web model (Ecosim) to evaluate the ecological consequences of future alternative management strategies
and the interaction of two different sets of life history characteristics for fishes at the top of the food web. Relatively
rapid turnover rates occur among the exotic forage fish, rainbow smelt, and its primary predators, exotic Pacific salmonids.
Slower turnover rates occur among the native lake trout and burbot and their primary prey—lake herring, smelt, deepwater cisco,
and sculpins. The abundance of forage fish is a key constraint for all salmonids in Lake Superior. Smelt and Mysis play a prominent role in sustaining the current trophic structure. Competition between the native lake trout and the exotic
salmonids is asymmetric. Reductions in the salmon population yield only a modest benefit for the stocks of lake trout, whereas
increased fishing of lake trout produces substantial potential increases in the yields of Pacific salmon to recreational fisheries.
The deepwater or siscowet morphotype of lake trout has become very abundant. Although it plays a major role in the structure
of the food web it offers little potential for the restoration of a valuable commercial or recreational fishery. Even if a
combination of strong management actions is implemented, the populations of lean (nearshore) lake trout cannot be restored
to pre-fishery and pre-lamprey levels. Thus, management strategy must accept the ecological constraints due in part to the
presence of exotics and choose alternatives that sustain public interest in the resources while continuing the gradual progress
toward restoration.
Received 10 December 1999; accepted 13 June 2000. |
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Keywords: | : fishes fisheries ecosystem food web Lake Superior Great Lakes modeling Ecosim Ecopath trophic interactions |
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