Crawdads colonize the West's waterways

 

Down South, they call them 'Cajun popcorn.' In the West, they're a menace.




MESQUITE WASH, Ariz. - On a spring-like Sunday afternoon, Mike Demlong, a biologist with the Arizona Game and Fish Department, and his 9-year-old son, Andrew, pick their way up a desert wash northeast of Phoenix, Ariz. Despite the dry winter, a stream trickles through Mesquite Wash, between its scrubby namesake trees and a few stouter cottonwoods.


From time to time, father and son crouch and peer at the bottom of a clear pool. Most are studded with black snails, but Demlong isn't looking for snails. He's in search of an armored predator that is wreaking havoc on Arizona's streams. In New Orleans, they call these crustaceans "Cajun popcorn." Demlong calls them crayfish; they're also known as crawdads or spiny lobsters.


Arizona has no native crayfish. But for decades, government agencies have released them into the state's waters to control weeds and to feed bass and other game fish.


Fishermen, who use crayfish for bait, have also helped the creatures spread. Once established, crayfish don't just feed the fish - they feed on fish, and on just about anything else they can get their pincers around.


"This gives a little idea what they can do," says Demlong, pointing to a six-foot-wide pool where the gravel bottom is bare of snails. Several other types of creek life, from algae to insects, are also noticeably sparser than in other pools.


Mesquite Wash has gotten off relatively easily. In other Arizona streams, researchers have documented declines in turtles, frogs and fish after non-native crayfish show up. "They're devastating aquatic ecosystems throughout the state," says Demlong.


This spring, Demlong is preparing a proposal to ban selling or transporting live crayfish in the state. Around the West, fish and game departments are waking up to the dangers of spreading these non-natives, though for many streams it could be too late.


A ravenous newcomer

Few understand the dangers of non-native crayfish better than biologist Philip Fernandez of Grand Canyon University, a private college in Phoenix. "I used to like eating them," he says, "but now I think of them as aquatic cockroaches."


He has watched a four-inch-long crayfish drown and completely consume a 10-inch garter snake. "You know those machines used for chipping branches?" he says. "That's what their mouths are like."


Fernandez has been studying wildlife in one small, unnamed stream in eastern Arizona's White Mountains for 13 years. He first found crayfish here seven years ago, apparently after some angler's well-meaning release of live bait. The changes he has witnessed since then are startling.


"They have transformed a clear, biologically diverse stream into a muddy stream that just has thousands of crayfish in it," says Fernandez. "First they eat the vegetation. There's not a scrap of vegetation left. They eat the pond snails, the mayfly larvae, caddisfly larvae, other insects. Then they go after the vertebrates. They eat tadpoles, fish, turtles, garter snakes."


Even the stream's brown trout have disappeared. Trout can eat small crayfish, but not larger ones, which devour the fishes' food supplies. The local population of Chiricahua leopard frogs may be doomed, too. The frogs have survived only in one pool, which the crayfish hadn't reached. But in the past year, crayfish have appeared here, too.


Fernandez and 10 helpers pulled more than 2,000 crayfish out of a short stretch of the stream one morning last summer, but missed others that had burrowed out of reach.


Scrambling for solutions

The problem is neither new nor limited to Arizona. Every other Western state has at least one native crayfish. It is the non-native crayfish that are causing problems.


In Nevada, the non-native Louisiana red swamp crayfish has nearly wiped out one of the three remaining populations of the endangered Pahrump poolfish. The poolfish go dormant in winter, making them easy prey, says Jon Sjoberg, a biologist with the Nevada Division of Wildlife. Sjoberg is also concerned about how the recent spread of crayfish to the Beatty area will affect the Amargosa toad, unique to that area.


In Northern California, the non-native signal crayfish is displacing the native Shasta crayfish, an endangered species. "We've been trying to remove the signals, but it's difficult to get all of them," says biologist Rebecca Miller with the California Department of Fish and Game.


Both Nevada and Utah forbid moving live crayfish from one water to another within the state. Other states, including California and Montana, may soon follow suit.


Montana biologists worry that imported crayfish could spread disease to the state's three native crayfish species. The state is already struggling to cope with the effects of the non-native parasite that's causing whirling disease in trout (HCN, 9/18/95: Tje West's fisheries spin out of control).


Montana allows residents to import live crayfish only for keeping as aquarium pets. Now, state fisheries officials are drafting a proposal to close that loophole, to be presented to the Montana Fish, Wildlife and Parks Commission later this year.


Montana biologist Jim Peterson says, "We're learning from experience that we need to be careful about introducing any exotic species, whether it's crayfish or anything else."


The author writes for the East Valley Tribune in Mesa, Arizona.




YOU CAN CONTACT...


  • Mike Demlong, Non-game Division, Arizona Game and Fish Department, 2221 W. Greenway Road, Phoenix, AZ 85023 (602/789- 3504); mdemlong@gf.state.az.us;


  • Philip Fernandez, Biology Department, Grand Canyon University, 3300 W. Camelback Road, Phoenix, AZ 85017 (602/789-3504);


  • Jim Peterson, Fisheries Division, Montana Fish, Wildlife and Parks, 4801 Giant Springs Road, Great Falls, MT 59405 (406/452-6181).

Copyright © 2000 HCN and Guy Webster