The sea lamprey, up close. (Photo courtesy of USFWS)
One of the Ten Threats to the Great Lakes is the decline of many of the native species. The lake trout has been in trouble from over-fishing and because of an invasive species called, the sea lamprey. Conservation agents use a pesticide to keep the lamprey down, but it’s expensive, and sometimes it kills other fish. Now, researchers have discovered a lamprey pheromone that could help the fight against the sea lamprey. Stephanie Hemphill has that story:
Transcript
In our next report in the series Ten Threats to the Great Lakes we hear about how a native
fish has been hurt by an invasive species that swam into the lakes through a canal. Lester
Graham is our guide through the series.
One of the Ten Threats to the Great Lakes is the decline of many of the native species.
The lake trout has been in trouble from over-fishing and because of an invasive species
called, the sea lamprey. Ever since it invaded the Great Lakes, scientists have been trying
to keep the invasive sea lamprey under control.
Conservation agents use a pesticide to keep the lamprey numbers down, but it’s expensive,
and sometimes it kills other fish. Now, researchers have discovered a lamprey
pheromone. They think the chemical attractant could be a big help in their fight against
one of the most destructive invasive species in the Great Lakes. Stephanie Hemphill
has that story:
The sea lamprey came into the Great Lakes through canals more than a hundred years
ago. The slimy parasites attach themselves to big fish and feed on them until they die.
Each lamprey can kill 40 pounds of fish in its lifetime.
Between sea lampreys and over-fishing, the big native fish, the Lake Trout, was wiped out
in the lower Great Lakes. Only a few survived in small pockets in Lake Huron. Lake
Superior is the only place Lake Trout survive in healthy numbers.
There’s an aggressive 15-million dollar a year program to keep sea lamprey numbers
down. Part of the effort is using a chemical called TFM that kills the lamprey.
Wildlife managers spread the lampricide in streams in the spring. It kills some of the
young lamprey as they swim down into the lake.
University of Minnesota biologist Peter Sorensen says he and other scientists noticed that
TFM kills not just the juveniles, but the larvae that live in the streambed too. They also
realized, after a stream is treated, very few adult lamprey come back to the stream to
spawn, or lay new eggs.
“And this led to an observation decades ago, which was key, that adult lamprey must be
selective in how they pick streams. They only pick a few, and if you remove the larvae
they don’t seem to go in there.”
Scientists suspected the larvae might play a role in the spawning migration of adults.
That might mean the larvae are putting out a pheromone that tells the adults it’s a good
place to spawn. Just one larva attracts a lot of adult lamprey, indicating the pheromone
is very potent.
It was up to Jared Fine to determine what the chemical is. Fine is a PhD student working
with Peter Sorensen. For two years he sifted through the water in tanks holding lamprey
larvae.
“Separating the different chemical compounds, testing them biologically, seeing which
ones have activity, coming back to the active ones, further separating them, and just
repeating this until you get down to the one or two or three compounds that have the
activity.”
Fine narrowed it down to three compounds. He purified them and gave them to a colleague in the chemistry department, Thomas Hoye. Hoye created a synthetic version of the most potent pheromone. He says it should be possible to produce it on a large scale, and that means it could be used to treat the
Great Lakes. The question is, how much would he need?
“You know, would it be a tank car load, would it be a football field, would it be a dump
truck? It’s none of those. Would it be a barrel? No. Is it a bucket-full? No. In
fact it’s only about 500 grams, that’s just one pound, would treat all that water for a
month.”
And that’s all it would take, because the lamprey only spawn for a month, but the
treatment would have to happen once a year. Peter Sorensen says when lamprey
approach a stream to spawn, their clock is ticking. They have a powerful urge to lay
eggs, and once they’ve done that, they die.
“They are driven animals. Frankly they’re kind of on autopilot and pheromones are
what’s driving that autopilot to a very large extent, and now that we’ve got it, I think we
can really powerfully use that to our advantage.”
Sorensen says fisheries managers could use the pheromone to attract more lampreys to
streams outfitted with traps.
“You know the key here is the fact that this pheromone is natural, safe, and should be
very inexpensive to add.”
Fisheries managers hope the pheromone will help reduce the cost of controlling the
lamprey and add a new weapon to their arsenal.
The news on lamprey couldn’t have come at a better time for wildlife managers
around Lake Superior. After years of relatively constant numbers, the lamprey
population jumped dramatically this year. Scientists say lamprey may be finding new
spawning grounds in the mouths of streams, where lampricide is less effective. They’re
hoping they can use the pheromone to draw the lamprey to traps further upstream.
For the GLRC, I’m Stephanie Hemphill.