Invasive sea lamprey reduced on Great Lakes after COVID-era surge

One of many prime invasive species threats to the Nice Lakes sportfish, the ocean lamprey, is on the decline after surging through the COVID-19 pandemic, when efforts to manage the invaders slowed or halted.

Grownup invasive sea lamprey numbers within the Nice Lakes have returned to pre-pandemic ranges when remedies had been restricted in 2020 and 2021, the Nice Lakes Fisheries Fee stated in its 2025 sea lamprey management report.

Some 37,800 grownup sea lampreys had been caught in 2025, just under the pre-COVID-19 three-year common of 38,167 lampreys between 2017 and 2019.

“If we fail to manage sea lamprey populations, our native fish populations would undergo tremendously,” stated Earl Provost, vice chairman of the fee.

“As we noticed in 2022 and 2023, sea lamprey populations might simply skyrocket if management efforts let up. We’re solely now getting again to a semblance of what issues had been like earlier than the COVID-19 pandemic, and there’s nonetheless a variety of work to be carried out.”

Wanting like one thing out of a science fiction/horror story, sea lampreys are parasitic fish – not eels – native to the Atlantic Ocean. As canals higher linked the Nice Lakes to the Atlantic Ocean, lampreys started arriving within the mid-1800s and early 1900s.

Sea lampreys are parasites, which feed by attaching themselves to fish with their sucking mouth, utilizing their tongue to rasp a gap by way of the fish’s pores and skin and consuming the blood and juices that stream from it. Every sea lamprey can eat as much as 40 kilos of fish throughout its parasitic part. One feminine sea lamprey can lay 100,000 eggs, of which about 10% survive, which quantities to 10,000 new sea lampreys.

Their invasion of the Nice Lakes prompted vital injury to native fish reminiscent of lake trout, whitefish, ciscos and walleye. When Nice Lakes populations peaked at about 2.5 million within the mid-Twentieth century, they killed 100 million kilos of Nice Lakes fish yearly.

Recognizing that the ocean lamprey downside was too large for states, Canadian provinces, and even particular person nationwide governments to deal with, the U.S. and Canada entered right into a treaty in 1954 that the next yr created the Nice Lakes Fishery Fee, a binational effort to manage the ocean lamprey and conduct scientific analysis on the issue.

The efforts embrace common remedies with lampricides, chemical compounds that successfully kill sea lamprey larvae with out inflicting vital hurt to different vegetation and animals, in additional than 200 Nice Lakes tributaries. The fee has additionally constructed about 50 boundaries on tributaries to stop grownup sea lampreys from accessing spawning habitats.

All informed, science-based management efforts have diminished Nice Lakes sea lamprey populations to 10% of their historic highs.

In 2020 and 2021, amid COVID-19, management actions reminiscent of lampricide purposes stopped altogether or had been scaled again to various levels on all 5 Nice Lakes as a result of restrictions imposed within the US and Canada through the pandemic. It prompted sea lamprey populations to extend dramatically.

Extra: Sea lamprey management efforts have slowed throughout COVID-19. It allowed the Nice Lakes invaders to flourish

In Lake Ontario — the one Nice Lake the place sea lamprey management efforts fully halted in 2020 and recovered solely 50% the next yr — the ocean lamprey inhabitants has elevated tenfold, in accordance with a US Geological Survey research. The variety of lamprey wounds on fish elevated considerably in Lake Ontario; for chinook and coho salmon additionally elevated greater than tenfold.

Though the abundance of grownup sea lampreys has declined in all 5 Nice Lakes by 2025, solely on Lake Erie are the numbers beneath fisheries managers’ goal.

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“This $5.1 billion trade might collapse if sea lamprey populations spiral uncontrolled once more,” stated Ethan Baker, chairman of the Nice Lakes Fishery Fee. “Nobody desires a repeat of the early days, when it was troublesome to discover a fish with out a sea lamprey wound. So we are going to proceed to work laborious – working with federal, state and tribal companions – to make sure lampricide remedies can proceed with out pause.”

Contact Keith Matheny: kmatheny@freepress.com.