Jim Johnson

In my last column we talked about how, ever since the last ice age, lake trout and walleye were the keystone predators of Lake Huron. As keystones, they groomed numbers of other species assuring they did not overpopulate, facilitating a balance between predator fish (the hunters) and their prey (the hunted). But overfishing and invasive sea lampreys virtually wiped out the lake trout and walleye of lakes Huron and Michigan and, by the 1960s, the lakes were overrun by invasive alewives, a prey fish from the Atlantic. To restore balance, Pacific salmon were introduced to the Great Lakes, and they quickly restored balance and became the foundation for a multibillion-dollar recreational fishery. Salmon, rather than our native predator fish, were turned to at first because salmon eggs were offered to Michigan from West Coast states and there were not enough eggs available to stock our native lake trout in the numbers needed. Plus, it costs much less to raise salmon than lake trout.

By the late 1970s, the salmon had fulfilled their mission, and a kind of balance had been restored. Fishery agencies could now turn their attention to restoring our native predators.

Between 1998 and 2004, three major developments enabled the recovery of lake trout in northern Lake Huron:

· Nearly complete disappearance of alewives from Lake Huron

· Effective control of sea lampreys originating from the huge St. Marys River – the last remaining stronghold for sea lampreys in the Great Lakes.

· Reduction in gill-net fishing by Native American fishers, as established by the 2000 Consent Decree.

Let’s have a look at each of these three factors.

Alewives: Alewives, although consumed eagerly by lake trout, contribute to thiamine (vitamin B) deficiency (see sidebar column – The Alewives Revenge). This deficiency impairs the survival of lake trout embryos and fry, preventing successful reproduction. In addition, alewives prey on trout fry, further hampering the population’s ability to sustain itself. Therefore, for lake trout reproduction to resume, alewife numbers had to be reduced so that lake trout would be forced into eating more healthy foods and fewer lake trout fry would be consumed by alewives.

Sea Lampreys: After about 1980, sea lamprey populations soared in the St. Marys River. The St. Marys is the outlet of Lake Superior and Lake Huron’s largest tributary. By the 1990s it was producing as many lampreys as all other Great Lakes tributaries combined. Thanks to increased funding by Canada and the U.S., as well as a one-time contribution of $4.5 million by the State of Michigan, the St. Marys was first successfully treated in 1998.

Stocking lake trout that show resistance to sea lamprey attacks is one way of enhancing the benefits of sea lamprey control. Sea lampreys have been in Seneca Lake, New York for at least 150 years. Lake trout reproduction persisted in Seneca Lake despite these lampreys. This suggested that Seneca lake trout might be a useful tool in lake trout recovery in the Great Lakes and, sure enough, lake trout of Seneca Lake origin stocked in Lake Huron proved to survive to

maturity and reproduced much more successfully than any other strain. Most stocked lake trout and almost all wild lake trout in Lake Huron today are of this Seneca Strain.

Reduction in gill-net effort: Although Michigan had converted its gill-net effort to trap nets, gill-net fishing prevailed in Treaty of 1836 waters of the upper Great Lakes. A Consent Decree of 2000 called for the conversion of half the Treaty Waters gill-net effort to the less lethal trap nets. This measure sharply reduced the kill of lake trout by commercial fishers pursuing lake whitefish. Unfortunately, the number of gill nets deployed by the Ontario commercial fishery remains an impediment to recovery, especially in southern Lake Huron.

The result: restored Lake Trout reproduction and the beginning of a gradual recovery.

All three elements – reduction in alewives, control of sea lampreys, and reduction in gill net bycatch – came together for northern Lake Huron between 1998 and 2004. Since about 2000, the number of wild lake trout has steadily risen. Most importantly, the abundance of mature, spawning-age lake trout has also climbed. Almost all the wild lake trout are of Seneca Lake strain. The recovery has been gradual and especially slow in southern Lake Huron, where spawning habitat is less abundant and proximity to Ontario commercial gill nets (gill nets are still the chief fishing gear there) means fewer lake trout survive to spawning age.

An especially gratifying outcome has been the increase in numbers of older, mature lake trout in northern Lake Huron. The DNR Alpena Fisheries Station determines lake trout ages by examining cross-sections of jawbone under a microscope. Just as foresters age trees by counting tree rings, fishery biologists count annual growth rings on the bone cross sections. Just 30 years ago it was rare to see lake trout older than about 10 years old; now lake trout are as old as 30 years. A 30-year-old lake trout female has many times more eggs than a 10-year-old. These older lake trout hold the promise of steady recovery of lake trout in Lake Huron’s future.

Jim Johnson worked as a research biologist at the DNR’s Alpena Fishery Station. He and the DNR’s research vessel, the RV Chinook, as well as Boat Captain Clarence “Tuffy” Cross retired to the Besser Museum