By Bert Bowers
The parasitic sea lamprey, one of the earliest exotic species accidentally introduced into the Great Lakes via man-made canal systems, created a problem that was recognized early on by people in the fisheries business. Beginning in the lower lakes in the 1930s and ’40s and reaching Lake Superior by the 1940s and ’50s, the lamprey problem turned into a disaster as one commercial fishery after another crashed.
In those early days, states and provinces were economically and technically unable to cope with the problem. For this reason, the United States Fish and Wildlife Service (USFWS) and its Canadian counterpart, the Department of Oceans and Fishes, were asked to look into the problem. It was decided by research biologists to concentrate control efforts on Lake Superior, since there was still a viable native lake trout fishery to be saved. Lake trout had been virtually wiped out in the lower Great Lakes by this time.
In the late 1940s, the various agencies concerned declared war on the sea lamprey. After nearly 50 years and many battles, the war still rages. It is fought quietly, for the most part, in many of the backwater areas of the Great Lakes - places like Michigan’s Two-Hearted River, Wisconsin’s Bad River, Ontario’s Batchawana River and other optimum sea lamprey-producing tributaries.
An early attempt to bring the lamprey population under control on Lake Superior tributaries was initiated on streams where sea lamprey were known to spawn, using electro-mechanical barriers called weirs. (I joined the USFWS in September, 1953, as a lad of 19 years and worked in this effort until retirement in 1988.) By 1956, all the known sea lamprey-producing streams in the United States and Canada on Lake Superior were blocked with the electrical barriers.
Preliminary studies showed that the adult parasitic sea lamprey spends 12 to 18 months in the Great Lakes, then migrates up a desirable stream to spawn and die.
The female lamprey produces about 65,000 eggs. The eggs hatch in the stream and the young larval lampreys, called ammocetes, burrow into the stream bed, where they spend three to seven years or more. During this phase of their life cycle, they are not parasitic to fish, feeding only on microorganisms.
After this phase, the animal transforms into a parasitic adult, leaves the stream bed and migrates to the lake to feed on fish for the next several months. Research has shown that a lamprey will consume about 40 pounds of fish to reach the breeding stage. Its favorite prey in Great Lakes waters appears to be lake trout. The following spring, adults swim back upstream to spawn, completing the life cycle.
In the beginning, the electrical weir was the only method of control available, but it could prevent spawning of only one generation of lampreys at a time and only if it worked 100 percent of the time, which was rare. If a barrier failed just during one night at the peak of a spawning run, a whole year’s class of lamprey was introduced into that particular stream. Since the weirs were electro-mechanical devices, there was plenty of room for failure.
At the same time control was being attempted by weirs, a more desirable tool was being researched. It was envisioned to be a chemical to kill lampreys, yet be harmless to non-target species in the streams. If such a chemical could be found and methods of using it in flowing waters could be developed, it would wipe out several generations of the parasite in one treatment. To this end, the USFWS set up a bio-assay laboratory in the late 1940s at an abandoned Coast Guard station in Hammond Bay, Michigan, and began testing chemical compounds.
Around 1958, after testing more than 5,000 compounds, the chemical Tri-Flouro-Methyl-Phenol (TFM) was found to fit all the requirements. It worked well in the lab and, after being field tested in small streams, it looked even better. TFM is an organic compound that is water soluble and, in a relatively short period, breaks down to harmless residuals. The chemical is registered with the Environmental Protection Agency.
The use of TFM brought the lamprey’s population under control in the early 1960s on Lake Superior and control swiftly followed on lakes Michigan and Huron. Numbers of spawning lampreys at the weirs were reduced by 90 percent by 1960.
Efforts in those early days were aimed at saving the commercial fisheries, an enterprise that supplied around 2,000 metric tons of lake trout annually from Lake Superior alone through the 1930s and ’40s. These fish harvests were reduced to a trickle through the late 1940s to ’60s and commercial fishing was almost completely eliminated by the various agencies involved.
Because of the management controls that were tried, native trout stocks in Lake Superior survived these lean years. A self-sustaining population is thriving in many areas of the lake today. According to an April 1996 news release from the Great Lakes Fisheries Commission, in some areas of Lake Superior populations are back to 80 percent of those that occurred before invasion of the sea lamprey.
Another positive result of lamprey control and fisheries management is the booming sport fishery in all of the Great Lakes. This activity brings about $2 billion annually into the state of Michigan alone.
Dr. Gary Klar is Field Supervisory Biologist at the USFWS Biological Station in Marquette, Michigan, and oversees sea lamprey control operations throughout the Great Lakes.