(WJET/WFXP/YourErie.com) — The population of sea lampreys in the Great Lakes could increase significantly in the next year or two, and it’s currently unclear how quickly the population can be culled back.
“They latch on with an alien, grotesque, teeth-filled suction cup mouth…” That’s how Dr. Marc Gaden, the communications director and legislative liaison of the Great Lakes Fishery Commission describes the sea lampreys. There’s no love lost there. “You only have to look at a picture to know that I’ve undersold just how grotesque they really are,” he adds.
Ugly though they may be, they’re not a direct danger to humans. Nor are they a danger to dogs that swim in the Great Lakes. Sea lampreys feed on cold-blooded animals. If they attach to a human, they’re “just hitching a ride,” Gaden said, and they’ll detach within a moment (they’ll be attached maybe long enough for a photo that can be ominously posted to the Internet, for example). Long-distance swimmers who have crossed Lake Ontario have complained about having to pick sea lamprey off as they swim.
“Again, they’re just hitching a ride, and if you’re not swimming across Lake Ontario, you don’t need to worry about it,” Gaden said. “Otherwise, they’re terrified of you, and they wouldn’t feed on you because you’re warm-blooded.”
But sea lampreys are a nightmare for fish. They attach with their suction-cup mouths and then use a spiny tongue to drill into the side of the fish. They feed on the fish’s blood and body fluids.
“They’re vampires,” Gaden said.
Impact and lifecycle
Each sea lamprey can kill more than 40 pounds of fish during its lifetime. Before scientists developed chemicals and tactics to control the lamprey population, they were killing 110 million pounds of fish per year.
“That’s much larger than the commercial catch rate was at the time — sea lampreys were taking more fish than humans when the control efforts started,” Gaden said.
And, man, can they breed. A single female lamprey can lay up to 100,000 eggs. Add that to the fact that fish in the Great Lakes were sheltered from sea lampreys throughout their evolution and therefore never developed the ability to fight them off. It’s not difficult to understand why sea lamprey have had a dramatic impact on the native fish populations ever since they made their way into the Great Lakes in the late 1800s. By 1939, Gaden said, sea lamprey were all the way to Lake Superior, and by the 1940s everybody began to realize how dire the situation was. Fishermen and other stakeholders lobbied their respective governments in the United States and Canada, and mitigation efforts got underway.
Scientists sought a way to remove the population.
“It’s easy to kill fish with a common piscicide (fish poison), but we only use that as a last resort,” Gaden said. Dumping piscicide into a water system kills all the fish — sea lamprey, lake trout, walleye, etc. “Say you have a pond full of snakehead fish, you can do it, but you’ll essentially reset the pond. In the Great Lakes system, that cure would be worse than the disease.”
It wasn’t until 1957 that scientists used a “pickle jar” test to discover a lampricide (lamprey poison). Gaden said scientists would put a couple of trout and a couple of lamprey in the same “jar,” introduce a chemical and then come back to check the result in the morning. More often than not, both the fish and the lampreys had died. Occasionally, just the fish had died. Finally, after some 7,000 chemicals were tried, they found just the right chemical to kill the lamprey and only the lamprey (“the lamprey is a primitive fish and can’t metabolize the chemical in the lampricide like the other fish can,” Gaden explained).
Sea lampreys spawn in rivers. The eggs are laid upstream in rocky areas, and the hatched larvae then swim downstream where they embed themselves in silty, sandy river bottoms. They live there for about four years before maturing and undergoing metamorphosis, becoming the parasitic form that’s so devastating to the great lakes.
Pandemic slows mitigation
Because the sea lampreys spawn in rivers, a quick solution was to build dams. Some 400 or 500 streams in the Great Lakes system are suitable for sea lamprey spawning. About 70 dams have been purposely built to curb lamprey spawning. Other dams were built for other reasons but they’re still effective in preventing sea lamprey spawning, Gaden said. That still leaves a lot of streams for spawning. And that’s where the lampricide becomes key.
The lampricide is applied to the streams, killing the larvae hidden beneath the sand. It kills some 98% of the larvae. Since the larvae spend about four years in the streams (essentially harmless to the ecosystem at that stage of their lifecycle), the Great Lakes Fishery Commission treats 25% of the streams each year. In doing so, they’re killing “four-year classes at once,” Gaden explained. That works out to about 100 to 120 streams that are treated with lampricide each year.
Leading up to 2020, the commission had noticed an uptick in lamprey numbers throughout the
Great Lakes, so it had ramped up its treatments. But then came the pandemic.
Pandemic restrictions meant teams couldn’t venture into the field to treat the streams, and that had definite impacts on the treatment schedules. In 2020, the commission only was able to treat about 25% of the streams it had planned to treat by the time the pandemic restrictions went into effect. When the pandemic restrictions eased in 2021, the commission treated about 75% of the streams it had planned to treat in 2021. Now in 2022, Gaden said the commission plans to complete its full schedule of stream treatments.
Good news, bad news
That brief lapse in treatments is bad news for the Great Lakes. Those lampreys have had that much time to develop and swim into the lakes where fish can’t shake them off and they’ll eventually return to lay 100,000 eggs each.
“We’re not going to really know until probably late this year or next year… the (lamprey) coming back in 2022 were survivors of the 2020 field season. We have biologists out there monitoring the spawning rate,” Gaden said. “Lampreys are spawning into late June, so we will know later this year how 2020 shook out. It’s reasonable to see a spike after having to defer most of the treatments.”
The good news, Gaden added, is that teams already had ramped up treatments the year before the pandemic.
“We serendipitously have never been better placed to weather something like a severely displacing pandemic,” Gaden said. “It could be the difference between setting us back a couple of decades as opposed to maybe a blip where we can get aggressive over the next couple of years to drive that down. We’re cautiously optimistic that it’ll be a blip.”
Sea lampreys prefer cold water, Gaden said. But if it seems like climate change’s warming temperatures are good news in the fight against sea lampreys, think again.
“Sea lampreys do well in cool water, and they get by in warm water,” Gaden said. “In Lake Superior, in some of those cold streams in the middle of nowhere, they live as larvae for up to 17 years before going through a metamorphosis. In some lakes, like Lake Erie, they’re more frequent because of the warmer environment there.”
Already, the commission had been considering upping its treatment schedule by 30% due to warming temperatures. Staying at least a step ahead of the sea lampreys is imperative.
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“If they bounce back, they’ll wipe you out and it will take a very long time to get it back,” Gaden said. But Gaden was remaining cautiously optimistic.