State of the Lake
Lake Superior as a whole is one Great Lake that continues to maintain much of its aquatic and terrestrial habitat intact. However, significant degradation has historically occurred in some locations across the basin. While significant progress on habitat improvement such as dam removals, culvert replacement, and riparian corridor restoration was achieved during this reporting period, significant impairments still exist, especially mining waste deposits around the Keweenaw Peninsula. Fish consumption advisories for legacy contaminants continue to be in place in most jurisdictions and new contaminant advisories (e.g. PFAs) are an emerging concern.
Lake Superior continues to maintain a diverse prey fish community comprised primarily of indigenous species. While prey fish abundance is low relative to previous reporting periods, prey species continue to be self-sustaining. Cisco recruitment was a concern during the reporting period, but cisco continued to support a viable commercial fishery in several jurisdictions and were reported in the diets of native fishes.
Lake trout declined to extremely low levels in Lake Superior due to commercial overfishing, accelerated by the invasion of sea lamprey. Rehabilitation began with sea lamprey control, allowing additional management efforts to be effective, such as strict harvest regulations and stocking. By 1996, the Lake Superior Committee (LSC) was able to substantially reduce stocking due to increased abundance of naturally reproducing lake trout populations. Currently, abundance of naturally reproduced lake trout is estimated to be at or above what are considered the best estimates of abundance prior to sea lamprey invasion. Because of this, the LSC believes the lake trout population is restored, and has achieved the 2003 Fish Community Objective of a “genetically diverse self-sustaining populations of lake trout that are similar to those found in the lake prior to 1940, with lean lake trout being the dominant form in nearshore waters, siscowet lake trout the dominant form in offshore waters, and humper lake trout a common form in eastern waters and around Isle Royale.”
Lake Superior continued to support production of lake whitefish at levels that support commercial harvest at or above the range of harvest values from 1990-1999 during the reporting period. During the reporting period, recruitment of lake whitefish increased and average recruitment levels were higher than the previous reporting period. Lake whitefish are expected to continue at these levels barring any significant change in regulatory or ecosystem processes.
While information on Lake Superior walleye is less robust, Lake Superior continues to support self-sustaining stocks of walleye at a number of locations across their historic range. Rehabilitation of some stocks (e.g. Black Bay, ON) is ongoing but positive progress is being made.
The number of self-sustaining populations of lake sturgeon in Lake Superior is increasing due to rehabilitation efforts and, in Wisconsin waters, provide for limited harvest opportunities. Full lake sturgeon rehabilitation may be challenging given that habitat limitations would require tradeoffs with current harbor uses (shipping and marinas) and with sea lamprey control (barrier dams).
Lake Superior brook trout continue to show mixed progress towards rehabilitation. Several stream populations of brook trout continue to persist in historic locations, with some doing relatively well, however, coaster brook trout continue to show limited signs of rehabilitation in Lake Superior proper in most locations. Coaster brook trout and stream resident brook trout are genetically similar, and it appears coaster brook trout are a life-history variant that moves into Lake Superior to feed and therefore grow larger. Currently, stream resident populations are being rehabilitated through in-stream habitat improvements. This coupled with conservative harvest regulations on Lake Superior, for brook trout that venture into the lake, is likely to improve the number of large brook trout captured in Lake Superior.
8.0 Pacific Salmon, Rainbow Trout, and Brown Trout
Lake Superior continues to support self-sustaining populations of Pacific salmon, rainbow trout, and brown trout. However, populations are augmented by stocking in some locations. These populations are meeting fishery objectives in that they appear to be compatible with restoration and management goals established for indigenous fish species. Stocking levels during the reporting period were the lowest on record.
Invasive sea lamprey populations must be controlled to prevent negative impacts on desirable fish stocks. Control efforts during the reporting period have not reduced sea lamprey abundance to target levels and fish community impacts continue to be seen. Estimates suggest that sea lamprey mortality continues to exceed harvest mortality in many locations in Lake Superior. Balancing sea lamprey control with habitat improvements, i.e. barrier removals, and resistance to lampricide treatments is important to maintaining fish populations at their current levels.
Lake Superior continues to see the introduction and spread of non-indigenous nuisance species through multiple vectors. Outside of targeted sea lamprey control, no programs are in place to reduce or eliminate non-indigenous nuisance species.
While data availability to assess Lake Superior species diversity is limited, Lake Superior continues to support four recognized lake trout forms (lean, siscowet, humper and redfin), and has retained its original cisco fauna, unlike the other Great Lakes. In addition, where assessments of other native prey species exist, populations appeared to be stable but lower in the past two reporting cycles as compared with the 1990s, which is likely the result of increased predator populations.