Lake trout in the Upper Great Lakes

The loss of lake trout has had a lasting impact on the health of Lake Huron and, to a lesser extent, Lake Superior.  As a result, multinational and interjurisdictional efforts were launched in the 1950s to rehabilitate these lake ecosystems.

Sea lamprey control
The control and eradication of sea lamprey in the upper Great Lakes is one of the principle mandates of the Great Lakes Fishery Commission, a bi-national organization founded in 1955.  In Canada, the duties of the Great Lakes Fishery Commission are carried out by Fisheries and Oceans Canada, which operates the Sea Lamprey Control Centre in Sault Ste. Marie, Ontario.

Sea lamprey control measures consist primarily of chemical treatment of spawning rivers and the installation and maintenance of barriers to lamprey migration.  The chemical treatments began in 1958 in Lake Superior tributaries, and in 1960 for Lake Huron.  The control program has been successful in reducing sea lamprey numbers to a fraction of their pre-control levels, but the efforts are ongoing.  The Ontario Ministry of Natural Resources contributes to the sea lamprey control program by estimating sea lamprey population size through monitoring the percentage of wounded lake trout landed in the commercial fishery.

Commercial fishery
A number of approaches have been used to reduce the impact of commercial fisheries on rehabilitating lake trout populations. Some areas of Lake Huron have been designated as fish sanctuaries, which restrict both commercial and recreational harvest of lake trout.  Seasonal and gear restrictions have also been implemented to reduce lake trout bycatch (lake trout that are caught in nets intended to catch other species).  With recent increases in lake trout abundance in some parts of Lake Huron, commercial quotas for lake trout have been developed.  These quotas strive to strike a balance between maintaining commercial fishing opportunities for species such as lake whitefish while at the same time limiting lake trout harvest to levels that will still allow lake trout population recovery.

Individual quotas have also been set for the commercial lake trout fishery in the deeper waters of Lake Superior.  Until full restoration is achieved, all quotas in the inshore zones are assigned as bycatch only.

Management Plans
A comprehensive approach to rehabilitating lake trout populations began with the development of lake-wide rehabilitation plans for Lake Huron in 1985 and for Lake Superior in 1986.  The plans promote interagency coordination for the rebuilding of self-sustaining lake trout populations in Canadian and U.S. waters.

Fish Community Objectives were established for Lake Huron (1995) and Lake Superior (2003), confirming the importance of lake trout as a dominant predator in the fish community and setting specific objectives and targets for its recovery.  A more detailed and focused plan specific to the Canadian waters of Lake Huron was completed in 1996.  The Lake Trout Rehabilitation Plan for Lake Huron (Canadian jurisdiction) focused on strategies that included stocking, rehabilitation zones, sea lamprey control, exploitation control, conservation of relic stocks, integrated assessment and research programs, and habitat management.

Stocking  
Efforts to restore lake trout in the Canadian waters of Lake Huron began in the 1950s with the stocking of lake trout (Figure 6).  Fish from these early stockings had poor survival due to repeated attacks by sea lamprey, and it became apparent that sea lamprey control was essential for lake trout rehabilitation. Vigorous efforts to control sea lamprey abundance began in the 1960s.

Research efforts on Lake Huron were also directed at other lake trout rehabilitation approaches.  The splake hybrid (a cross between a lake trout and a brook trout) was developed in the 1950s.  It was believed that an earlier maturing trout would have a greater chance of reproducing before it became large enough to be vulnerable to sea lamprey predation.  Lake Huron was stocked with splake and backcross hybrids (crosses between a splake and a lake trout) from the 1960s until the 1980s (Figure 6).  The lack of natural reproduction of these hybrids and the eventual suppression of sea lamprey to levels that provided improved chances of survival of lake trout resulted in the discontinuation of hybrid stocking.  Since 1996, only pure strain lake trout have been stocked into the Canadian waters of Lake Huron.  These include strains from Michipicoten and Slate Island on Lake Superior, Lake Manitou on Manitoulin Island and Parry Sound and Iroquois Bay, remnant strains from Lake Huron.

In Lake Superior, stocking of pure strain lake trout began in the early 1950s and peaked in the mid-1980s (Figure 7).  The recent recovery of lake trout populations in most of Lake Superior has reduced the need for stocking.  Stocking is now restricted to parts of eastern Lake Superior where lake trout population levels are still low.   

The ultimate goal of stocking programs is to re-establish self-sustaining adult populations that can reproduce, restore ecological function, and support fisheries without additional intervention.

Figures 6 and 7: Number of lake trout stocked in Ontario in the upper Great Lakes from 1950 to 2009.