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.
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.
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