American Intruder Lurks In Scottish Streams, Clawed And Hungry

American Intruder Lurks In Scottish Streams, Clawed And Hungry

1:14pm Oct 12, 2014
In the northwestern United States, this crayfish would be just a friendly bit of local fauna. But in Scotland, it's an invasive species wreaking havoc on trout streams.
In the northwestern United States, this crayfish would be just a friendly bit of local fauna. But in Scotland, it's an invasive species wreaking havoc on trout streams.
Ari Shapiro / NPR
  • In the northwestern United States, this crayfish would be just a friendly bit of local fauna. But in Scotland, it's an invasive species wreaking havoc on trout streams.

    In the northwestern United States, this crayfish would be just a friendly bit of local fauna. But in Scotland, it's an invasive species wreaking havoc on trout streams.

    Ari Shapiro / NPR

  • North American signal crayfish were introduced into England and have made their way north to Scotland.

    North American signal crayfish were introduced into England and have made their way north to Scotland.

    Ari Shapiro / NPR

Forget Nessie: there's another insidious creature living in the waters of Scotland.

The story starts in the streams and lakes of the northwestern United States, where North American signal crayfish are a familiar sight. Turn over a rock and you may well encounter one.

But in Scottish streams and lochs, these creatures are intruders.

In the United States, we often hear about invasive Asian carp, zebra mussels or snakehead fish from China that take over American waterways. It's a two-way street: American species are causing chaos in other parts of the world, too.

And in Scottish waters, home to prize-winning trout, American crayfish may be destroying the catch.

'Hundreds And Hundreds And Hundreds Of Them'

Allen Pleus, with the Department of Fish and Wildlife in Washington State, says that the signal crayfish is an important species in his region. It's the only native crayfish species, and the freshwater crustaceans are are just another part of the ecosystem.

"They play well with others," he says. "They've learned to be good neighbors with the other native species."

They eat aquatic insects and larvae; raccoons and herons, in turn, eat them. The system works.

But those same crayfish wreak havoc in Scottish waters like Clyde's Burn — a stream in Scotland where anglers from all over the world come to fish.

Matt Mitchell has been casting his line into these waters for about 40 years. "This area is probably, if not the best, certainly one of the best trout fisheries in the world," he says.

One day Mitchell got a call from an angler friend. The conversation changed Mitchell's life.

"He phoned me and said, 'I think we have a problem. You'd better come look at this,' " Mitchell says.

He jumped in the car and headed to the river.

"I could not believe the number of crayfish that were in this part of the river," he says. "You could literally walk across the river standing on crayfish. You couldn't walk without standing on a crayfish, they were so numerous!"

The North American signal crayfish, which had been introduced to English waters decades ago and spread steadily north, were taking over.

"What we did initially was just hand-catch them," Mitchell says, "hundreds and hundreds and hundreds of them."

There was some pinching involved. "I'll not repeat what the language was like," Mitchell says. "But they were big animals. I mean, some of these things were about 10, 12 inches long."

At that size, they don't even look like crayfish; they look like lobsters. Animals that big, Mitchell says, are more than a decade old; he guesses they've been in the river for 12 years.

No Trout Food, No Trout

The problem isn't just the size or quantity of the intruders; it's that the signal crayfish eat the same insects and larvae as the prize-winning trout that are native to these streams.

Mitchell's colleague Ian Miller is the man who first placed that concerned phone call from the Clyde Burn all those years ago; Mitchell calls him the best Clyde angler alive.

With the arrival of the crayfish, Miller says, "Stoneflies are gone — basically wiped off the face of the Earth."

That's a problem, because stoneflies are an important food for the fish. No trout food means no trout.

At the river, Miller pulls up a trap from the water to demonstrate. The plastic cage is alive with crawling, clacking crayfish — about a dozen of them, dark reddish-brown with giant claws, climbing all over each other inside the trap.

Crayfish like these can be a delicacy, but Scotland has decided that encouraging people to eat them would just create a market and make people spread them more widely.

As a result, anyone who pulls crayfish out of a Scottish river is legally required to kill them. The quickest way, Ian says, is to stomp them beneath a boot.

Fighting Invaders In Home Territory

Allen Pleus, the naturalist back in the Pacific Northwest, commiserates with the Scottish anglers.

Turns out, Washington State is struggling with a similar problem.

"Unfortunately, we now have our own invasive-species crayfish in this area — mostly red swamp crayfish from the southern United States," he says.

That's right. At the same time that the North American signal crayfish are taking over rivers and streams in Scotland, they're being crowded out of rivers and streams in their native habitat by other invasive crayfish — interlopers from Louisiana.

And those signal crayfish that are dominating streams in Scotland? In America, Pleus says, "They're considered wimpy in some cases — that they don't put up enough of a fight with these non-native species."

The serpent — or in this case, the crayfish — eats its tail.

Copyright 2015 NPR. To see more, visit http://www.npr.org/.

Transcript

ARI SHAPIRO, HOST:

Now we have a real-life fish tale about an insidious creature living in the waters of Scotland. And we're not talking about Nessie. This story actually begins in the United States.

Years ago, when I was a kid in Portland, Oregon, my brothers and I would go to nearby Fanno Creek. We'd turn over rocks or lower a piece of raw meat on a string into the water. And we'd pull out a crayfish - specifically a North American Signal Crayfish.

ALLEN PLEUS: They're important species in our streams and lakes. They are the only native crayfish that we have.

SHAPIRO: Allen Pleus is at the Department of Fish and Wildlife in nearby Washington state. He's very familiar with this species of freshwater crustacean.

PLEUS: They play well with others. They've learned to be good neighbors with the other native species.

SHAPIRO: So I would imagine that raccoons and herons eat them. They eat aquatic insects and larva and everyone lives happily ever after until they get eaten by someone else.

PLEUS: That's a good way to say it. Yeah, it's part of that system.

SHAPIRO: I never imagined that as an adult, I would find those same creatures wreaking havoc in Scottish waters.

MATT MITCHELL: This area is probably - if not the best - certainly one of the best trout fisheries in the world.

SHAPIRO: We're standing next to stream called Clyde's Burn. Anglers come from all over the world to fish here. Matt Mitchell has been casting his line into these waters for about 40 years. One day he got call from an angler friend that literally changed his life.

MITCHELL: He phoned me and said I think we have a problem. You better come up and look at this.

SHAPIRO: Mitchell jumped into the car and headed to the river.

MITCHELL: I couldn't believe it myself. I could not believe the number crayfish that were in this part of the river.

SHAPIRO: What did you see?

MITCHELL: I mean, you can literally walk across the river standing in crayfish. You couldn't walk without standing on a crayfish. They were so numerous.

SHAPIRO: These were not just any crayfish. The North American Signal Crayfish were taking over. They had been introduced to English waters decades ago and spread steadily north. And these guys were big.

MITCHELL: What we did initially was just hand catch them - hundreds and hundreds and hundreds of them.

SHAPIRO: Did you get pinched?

MITCHELL: Oh, initially, of course you did. (Laughter) I'm not going to repeat what the language was like. But they were big animals. I mean, some of these things were about 10 inches, 12 inches long.

SHAPIRO: That's a lobster. That's not a crayfish, that's a lobster.

MITCHELL: That's a big animal. That's an animal that's about, you know, 10, 12 years old. They've been in our rivers for about 12 years we reckon.

SHAPIRO: In the United States, we often hear about invasive asiatic carp, zebra mussels, or snakehead fish from China that take over American waterways. Turns out it's a two-way street. American species are causing chaos in other parts of the world too. In Scotland, the North American Signal Crayfish eat the same insects and larva as the prize-winning trout that are native to these streams.

MITCHELL: Here's a friend and colleagues of mine, Ian.

SHAPIRO: Hi, Ian. I'm Ari. Nice to meet you. Welcome.

IAN MILLER: Hi. Hi.

SHAPIRO: Ian Miller is the man who placed that you'd better get over here phone call from Clyde's Burn all those years ago.

MITCHELL: I would say Ian is the best Clyde angler living at the moment, by far.

SHAPIRO: And what kind of changes have you seen with the arrival of the crayfish?

MILLER: Stoneflies are gone - basically wiped off the face of the earth.

SHAPIRO: And that's an important food for the trout.

MILLER: That's an important food.

SHAPIRO: No trout food means no trout. The night before we met him, Ian Miller dropped a couple of traps in the water using a dead fish for bait. As we peered over the banks, he pulled the first plastic cage out of the stream. It was alive with crawling, clacking crayfish.

MITCHELL: A dozen or more crayfish in it.

SHAPIRO: Oh, my God. They're huge. Oh, there's - yeah, there's, like, a dozen of them climbing all over each other. They're beautiful. I mean, they've got these enormous claws. They're dark reddish brown with a hint of blue at the joint of the claw.

Crayfish can be a delicacy. But Scotland has decided that encouraging people to eat them would just create a market and make people spread them more widely. So anyone who pulls crayfish out of a Scottish River is legally required to eliminate them.

So these now have to be killed having been removed from the river. How will you do that?

MITCHELL: Under my boot.

SHAPIRO: Really?

MITCHELL: That's the quickest and convenient way.

SHAPIRO: All right, well, with apologies to any squeamish listeners, let's get the sound of this.

I described this scene to Allen Pleus, the naturalist back in the Pacific Northwest. He commiserated with the Scottish anglers. Turns out, Washington state is struggling with a similar problem.

PLEUS: Unfortunately, we now have our own invasive crayfish species in this area - mostly Red Swamp Crayfish from the southern United States.

SHAPIRO: Wait a minute. I'm doing a story about the North American Signal Crayfish taking over rivers and streams in Scotland. And you're telling me they are being crowded out of rivers and streams in their native habitat by other invasive crayfish that have been brought in from Louisiana?

PLEUS: Yes. The native Signal Crayfish - they're considered wimpy in some cases - that they don't put up enough of a fight with these non-native species.

SHAPIRO: The serpent eats its tail - or in this case, the crayfish. This is WEEKEND EDITION from NPR News. Rachel Martin is back next week. I'm Ari Shapiro. Transcript provided by NPR, Copyright NPR.

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