The Lamprey: Putting a bad guy into perspective

Vampire, blood-sucker, parasite – take your pick. The terms have all been used to describe the sea lamprey, which invaded all the Great Lakes by the 1940s and kills native fish by sucking up their bodily fluids.

It’s a behavior ruining more than the invader’s reputation.

Most people don’t know that native lamprey species co-exist peacefully in the lakes, said Philip Cochran, a professor of biology at Saint Mary’s University of Minnesota.

“Native lamprey have definitely suffered from what people know about sea lamprey,” he said.

Two native species are parasitic like the sea lamprey — the chestnut and silver lampreys. They feed on smaller fish than those that sea lamprey feast on and rarely kill them.

There are also two non-parasitic native species: the American brook and northern brook lampreys. These lampreys start their lives like all lampreys do as filter-feeding larvae living in stream beds. But once it comes time to mature they don’t become parasitic and instead live off their body stores until they spawn and die.

Both use the same habitats and eat the same stuff, said Mike Jones, chair of the department of fisheries and wildlife at Michigan State University.  “It’s only when they transform to the adult …then they diverge.”

These and other native lamprey species like the Ohio lamprey and southern brook lamprey live in inland waterways of Great lakes states.

At first glance, lampreys may all look alike. And in many ways they are.

They all have similar life cycles and habitats. And lamprey are attracted to similar pheromones — chemicals one individual releases to affect the behavior of another. Scientists speculate that sea lampreys detected these chemicals emitted by their native cousins when they first entered the lakes and followed them to find suitable spawning grounds.

But “native lamprey don’t get nearly as big,” Jones said.

Sea lamprey measure up to two feet. Native parasitic lampreys measure from four to thirteen inches. Their non-parasitic counterparts measure between four and seven inches.

Lampricides and other hazards

The U.S. and Canada spend about $15 million a year controlling the sea lamprey, Jones said. Methods include poisons that kill lampreys — including native species.

The saving grace is that is the native lampreys’ habitat is often distinct of sea lampreys, Jones said.

Native habitat can be blocked from sea lampreys by obstacles like dams, making lampricides unnecessary.

In some areas native populations repopulate fairly quickly after they are poisoned, Jones said.

But that’s not always the case.

Cochran says that northern brook lamprey used to be found in Wisconsin’s Brule River.

“That’s a system that has been treated for sea lampreys and we haven’t been able to find northern brook lamprey there in recent years,” Cochran said. “So that’s an example of a place where [a native lamprey] may have been lost.”

Other human activities, like pollution and the construction of dams, also kill the natives.

The parasitic Ohio lamprey is one such victim.

“They are a very migratory species with a complex life history and seem to have declined about the same time the dams were constructed on the Ohio River which fragmented their habitat significantly,” John Navarro, a program administrator of the Ohio Department of Natural Resources, wrote in an e-mail.

But counting  a secretive creature like the lamprey isn’t easy.

“They are an extremely difficult species to capture so they may be more abundant than what we actually realize,” Navarro wrote.

Paired Species

Native lampreys are considered “paired species” meaning that scientists think that non-parasitic ones evolved from their parasitic pair. Some studies suggest that some pairs are genetically identical.

“The belief is that that every species of non-parasitic lamprey evolved from a parasitic lamprey and gave up the parasitic stage,” Cochran said.

The American brook lamprey evolved from the chestnut lamprey. And the Southern brook lamprey, found in Minnesota and Wisconsin, evolved from the silver lamprey. The sea lamprey is not known to have a non-parasitic match.

But Cochran says that non-parasitic species might still have the genetic coding to become parasitic, even though they gave up that stage long ago.

Normally American brook lamprey are 4 to 6 inches long, Cochran said. “But every once in awhile we find a giant.”

The giants are about the size of the sea lamprey.

Cochran found in the giants’ stomachs the parasites that sea lamprey carry and that non-parasitic species usually don’t.  Their presence of  implies that this non-parasitic lamprey fed in a parasitic manner.

The fact that we find these gigantic non-parasitic lampreys with these parasites in their guts may mean they have the genetic code to become parasitic, Cochran said.

“That’s just a theory,” he said.

Mistaken identity

Whether native lamprey populations need protection is unclear.

“At a global level I don’t think we have to worry so much…however, within some states or within some provinces, some of these native lampreys may be very rare so I think that it would be possible to eliminate them from states and provinces if we’re not careful,” Cochran said.

In the Pacific Northwest, the parasitic Pacific lamprey is culturally significant to some Native American tribes and is a traditional food and medicine source. Tribes have called for its conservation.

But in the Great Lakes lamprey don’t seem to be revered.

Jones has never heard of a lamprey being killed because it’s a lamprey. But he said it may happen from time to time.

And it does.

“I used to work on a creek in Wisconsin where there were American brook lamprey — they’re non-parasitic,” Cochran said.

“I talked to the land owner and they said they would kill them every time they saw them…because they assumed they were harmful.”