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Those nasty sea lamprey are making a comeback in Lake Superior

They kill off native fish and their numbers are going up.

An invader that was once a threat to wipe out the Great Lakes fishing industry is making a comeback in Lake Superior. 

A new report from the Great Lakes Fishery Commission says sea lamprey numbers have rebounded in Lakes Superior and Erie. Which is kind of weird because the population is "historically low" in the other three Great Lakes. 

One lamprey can kill up to 40 pounds of fish in its lifetime, so people involved in the $7 billion-a-year Great Lakes fishing industry don't want them around. 

Why are there more?

Scientists are not sure how to explain the lamprey rebound in Lake Superior. 

There are a few theories, though. They may be bouncing back after a couple especially harsh winters in the middle of this decade. 

Or maybe it's because the fish they prey on (trout, whitefish, salmon, sturgeon) are more abundant. Warmer water temperatures are another possibility. 

A spokesman for the Great Lakes Fishery Commission tells the Duluth News Tribune the goal is to keep lamprey numbers in Lake Superior down to 45,000. Right now there are about 100,000, Marc Gaden says. But he points out that back in the 1950s there were 800,000.

What are these things?

As the name suggests, sea lamprey live out in the ocean. But about a century ago they started swimming into ship canals and eventually made their way through all the Great Lakes. 

They have a mouth like a suction cup and they use it to attach themselves to the scales of a fish. They have lots of teeth and a razor sharp tongue and once they're locked onto a fish they drill right through its side and suck out its body fluids. 

The fish out in the ocean can live through this – so for them the lamprey is a parasite. But for our more tender Great Lakes fish a lamprey is usually fatal. 

How do we stop them?

When the sea lamprey's Great Lakes invasion was at its peak in the '50s they were killing more than 100 million pounds of fish per year. 

In 1955 Canada and the U.S. formed the Great Lakes Fishery Commission to do something to stop them. And they did

The main tool they use is a poison – a lampricide. But the commission also uses barriers and traps against them. 

David Ullrich, who chairs the commission, says without those control measures, lamprey would wipe out the Great Lakes fishing industry. He says the lamprey are here to stay, but these days they're only taking 10 million pounds of fish a year instead of 100 million. 

Biologists have identified a few places on Lake Superior that seem to be hotspots for lamprey and are targeting those places for extra treatment. 

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