Thursday, June 28, 2007

Appreciating Illinois Crayfish

Appreciating Illinois Crayfish

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Crawdad. Mudbug. Crawfish. Crayfish. Whatever name you know them by, you probably don’t associate these lobster-like, freshwater crustaceans with the traits that give other wildlife their appeal. Crayfish are not warm and fuzzy, and they don’t sing or sport much color. (They do make great eating, but that’s another story.)

I checked in recently with Chris Taylor at the Illinois Natural History Survey to get the scoop on crayfish in our state. Taylor is a crayfish biologist and Curator of Crustaceans there, and he’s eager to help people understand the important role crayfish play in aquatic ecosystems. [Photo: Chris Taylor celebrates the unexpected discovery of a Rusty Gravedigger crayfish outside Mobile, Alabama. This species was formerly thought to be on the verge of extinction, but Taylor and others have found enough additional populations of it to ease that concern.]

Although to most people a crayfish is a crayfish, there are actually 360 species of them in the U.S., 24 of which occur in Illinois. Crayfish inhabit every aquatic environment in the state, from the smallest creeks and ponds to the largest rivers and lakes.

Crayfish that live in permanent water bodies typically spend the daylight hours concealed under rocks or woody debris. Other crayfish, known as burrowers, spend much of their time in tunnels and chambers they excavate in the ground. Some burrowers inhabit the margins of water bodies, but others live in habitats where there is no surface water for much of the year. You’ve likely seen the entrances to crayfish burrows even if you didn’t know what you were looking at. They are recognizable by the mud chimneys that rise several inches above them, which are formed from material that crayfish excavate with their claws.

All Illinois crayfish are most active from dusk to dawn, when they come out from under cover to forage for food and seek out mates. Depending on circumstances, crayfish may eat just about anything they can get their claws on, including plant material and carrion. But recent studies suggest they prefer live animal food--insects, snails, and even small fish. Crayfish in turn serve as a critical food source for sunfish and bass, but also show up on the menu for any number of wading birds, small mammals, reptiles, and amphibians.

Aside from biologists and environmental writers, I suppose few adults bother to ever catch crayfish. But if you get children into shallow, clear water, and show them how to find crayfish by turning over rocks, you may have trouble getting them to stop. Crayfish flee danger by a powerful flip of the tail that propels them backward. They are just fast enough to be difficult to catch, but not so fast as to be impossible.

There are two important things people can do to help promote the health of crayfish populations in Illinois. The first is to support efforts to conserve and restore aquatic environments. The second is to never release crayfish into a body of water they weren’t taken from. Many species of crayfish occur in very limited ranges, and so can be lost altogether when aggressive outsiders are introduced. One invader, the rusty crayfish, which was probably introduced by anglers dumping out unused live bait, has already displaced native crayfish from many waters in the northern half of Illinois.

Although the role of crayfish in aquatic ecosystems has been sometimes neglected in the past, scientists like Chris Taylor are working hard to further our understanding of them today. That understanding benefits all of us who love the outdoors and value the health of natural resources.

Article "The Rusty Crayfish in Illinois" from Illinois Natural History Survey Reports.

Sea-Grant fact sheet on Rusty Crayfish