DULUTH — The bad news is that there are still too many sea lamprey in Lake Superior to suit the Great Lakes Fishery Commission and protect trout and salmon populations. The good news, however, is that lamprey numbers are dropping some.

That was the report Tuesday, Nov. 12, from the commission that oversees fish populations and lamprey control efforts across the Great Lakes.

Despite decades of efforts to kill lamprey by poisoning their young in spawning streams, and by blocking the adult lamprey from swimming upstream, lamprey numbers had been growing in Lakes Superior in recent years and hit modern record numbers in 2017. That means more lamprey were killing more trout and salmon and reducing fish available for people and the $7 billion annual Great Lakes fishing industry. The Lake Superior fishery is valued at $154 million annually for Minnesota alone.

Lake Superior lamprey numbers hit an estimated 220,000 in 2017, well above the goal of 48,000 set by the commission to protect fish. The population now is estimated at 180,000, still high but far from the 780,000 before lamprey control started in 1958, said Marc Gaden, spokesman for the commission.

The commission’s lamprey targets are set at a level scientists believe can sustain fish populations in each lake. While still above that level, surveys show fewer lake trout are showing wounds or scars from lamprey attacks, the commission said in its report.

In response to the high population in 2017, commission officials ramped-up lamprey control efforts in 2019 in Lake Superior, and that should lead to far fewer of them by about 2021, Gaden said. In Lake Michigan and Lake Ontario, lamprey numbers remain near historic lows. They are stable in Lake Huron and also higher than goal in Lake Erie.

Sea lamprey swim in Lake Superior looking for fish to attach to with their suction-cup mouths. They can injure and even kill fish by sucking out their blood and body fluids. Contributed photo.
Sea lamprey swim in Lake Superior looking for fish to attach to with their suction-cup mouths. They can injure and even kill fish by sucking out their blood and body fluids. Contributed photo.

Lamprey are by far the most destructive of all invading species in the Great Lakes, nearly decimating fish populations by the 1950s before scientists figured out how to selectively target the parasite in streams where they spawn.

Sea lamprey are native to the Atlantic Ocean but have been an unwelcome nemesis in the Great Lakes since they invaded through new shipping canals in the early 1900s. They have no natural predators in the Great Lakes. Sea lampreys feed on the blood and body fluids of fish by attaching to them with a tooth-filled, suction cup mouth and file a hole through the fish’s scales and skin with a razor-sharp tongue. The average sea lamprey kills up to 40 pounds of fish during its adult, parasitic stage. Sea lampreys prefer trout, salmon, whitefish and sturgeon, but they also attack smaller fish such as walleye and perch.

Sea lampreys successfully reproduce in more than 500 Great Lakes tributaries and thus, the battle to keep their populations in check requires an ongoing effort. Before control efforts began more than 60 years ago, sea lampreys killed an estimated 103 million pounds of fish per year across the Great Lakes. Today, because of ongoing control, sea lampreys kill less than 10 million pounds annually.

The Great Lakes Fishery Commission was established by the governments of Canada and the United States in 1955 as a response to the catastrophic damage wrought by the sea lamprey invasion. In addition to poisoning lamprey larvae each year, the commission also uses traps and barriers to keep them from spawning.

“Keeping sea lamprey populations in check is absolutely critical if we want a fishery in the Great Lakes,” said Jim McKane, chair of the Great Lakes Fishery Commission, in a statement. “Each year, we must wage the battle anew. … Sea lamprey are here to stay. Fortunately, we can control their populations such that the damage they inflict on the fishery is a fraction of what it once was.”