Sympathy for the Lamprey

"Lampreys don't charm most people," begins a pamphlet from the Minnesota Sea Grant.

Truer words, my environmental research friends, truer words.


Yes, it's hard out there for a lamprey. Already cursed with a face not even their mothers (who die shortly after spawning) could love, these fish were further saddled with 50 years of bad PR brought on when one invasive species, the sea lamprey, moved into the Great Lakes and wreaked a trail of parasitic havoc from New York to Minnesota. Lost in the shuffle were several native lamprey species, some of which aren't even parasitic. Despite living in the Great Lakes for 1000s of years in co-evolved cooperation with other fish, non-invasive lamprey have paid the price for their cousin's misdeeds.

The problem stems from the (really fascinating) lamprey life cycle. Instead of having a short childhood and many years of maturity, lamprey basically spend most of their lives as larvae, buried in the mud at the bottom of stream beds*. They survive this way, feeding on microorganisms filtered out of the water, for anywhere from three to seven years, depending on the species. (Insert your own joke about college students here.) The adult stage of life, in contrast, can be as short as a single breeding season. In fact, some non-parasitic species don't even eat after becoming adults. Their digestive tracts just wither away and they use stored fat for energy during the short time they have left on Earth.

Lamprey's bottom-feeding phase basically creates a captive audience, in so much as "captive audience" means "conveniently having lots of lamprey in one place so you can poison them."

Now, before you call PETA, there's a good reason for the lampreycide. Sea lamprey are an invasive species that first entered the Great Lakes probably around the 1930s, when canals were opened allowing the lamprey to swim around Niagara Falls. Sea lamprey are big, and hungry, feasting on the blood of fish. And, for all but the largest fish, the embrace of the sea lamprey usually means death. (Native parasitic lamprey, by contrast, are much smaller and usually don't kill fish.) The Departments of Natural Resources in several states have been poisoning the streams favored by invasive sea lamprey larvae in order to save native fish since the 1950s.

The good news: The poison used is pretty lamprey specific and (again, because of that long larval cycle) DNR officials usually only need to poison a given stream once every four years or so.

The bad news: The poison will also kill native lamprey (which often live in the mud alongside the sea lamprey). The natives haven't been driven to the point of species endangerment by lamprey poisonings, says Phil Cochran, lamprey expert and chair of biology at Saint Mary's University of Minnesota. But geographic populations of these friendly, neighborhood lamprey have been threatened, and even wiped out.

So, over the last several decades, the DNR has been working to improve their aim, using both new control methods and a better understanding of native lamprey habitats. For instance, Cochran says, today we know that native lamprey often live further upstream than sea lamprey, so control crews can apply the poison at a point in the stream where it won't affect most of the native larvae.

And new, poison-free, methods of control are under research. One idea is to catch male sea lamprey and chemically sterilize them. "You release those males into wild populations and they dilute the breeding effort," says Cochran. "It will take a while to see whether this works with sea lamprey, but it's been used successfully on insects before."

Pheromones are also a possibility. Adult lamprey are attracted to chemicals released by larval lamprey. In fact, Cochran says these chemical signals might be the thing that helps lamprey make their way from lakes to the breeding grounds in streams. Scientists don't yet know whether these chemicals are specific to species but, if they are, they could be used to lure sea lamprey into a trap. (Insert Admiral Akbar joke here.)

*I, for one, will be thinking twice about squishing my toes through the mud at the bottom of stream beds from now on.

Image courtesy Flickr user edans, via CC.