The Wyoming Game and Fish Department is asking the public to be on the lookout for the rusty crayfish, an aquatic invasive species that’s turned up in the Laramie River watershed.
Anyone who finds one should report the sighting and location to the department, preferably with a photo. It’s against the law to transport or possess aquatic invasive species.
“Tell us where they’re at, and don’t move them,” said Laramie Region fisheries supervisor Bobby Compton.
The rusty crayfish is native to the Ohio River Basin but has been moving steadily west, transported by humans, and has invaded several surrounding states in addition to Wyoming. In 2006, the rusty crayfish was discovered in Wagonhound Creek, a tributary of the North Platte River, after been illegally introduced into a nearby private pond and then escaping.
Compton said Game and Fish has been working to rid that creek of the invasive species and making progress. It turned up in the Laramie River when biologists were doing sampling last fall.
An investigation is underway about how the crayfish was introduced into the Laramie River, but Compton said it was likely through a hatchery stocking a private pond years ago with fish as well as forage — the forage being the rusty crayfish. The department doesn’t sample private waters, so fisheries biologists don’t know where they are in the state until they show up in public waters.
“We don’t have a good handle on where they may or may not be,” he said.
The rusty crayfish has made Wyoming’s list of most-wanted aquatic invasive species, reserved for the offenders deemed the biggest threat to local habitats. That list includes zebra and quagga mussels, New Zealand mudsnails, Asian carp and several aquatic plants.
Rusty crayfish are 3-5 inches long with a grayish-green body and distinct reddish spots on each side the carapace. The spots are fingerprint-sized and located right where one might pinch a crayfish to pick it up.
“They’re really obvious,” Compton said of the spots.
When introduced in non-native environments, rusty crayfish are aggressive and prolific. They displace native crayfish species, reduce the amount and types of aquatic plants and invertebrates, and may reduce fish populations. Their diet includes the mayflies and stoneflies important for fish species.
They may also reduce the quality and quantity of habitat available for the hornyhead chub, a rare species found only in the Laramie River drainage.
Rusty crayfish prefer areas with rocks, logs and other debris as cover. They can live in lakes or rivers and prefer cool water. Even a single female can establish a new population because she stores sperm from a male until her eggs are ready to fertilize.
“They’re opportunistic,” Compton said.
Compton said biologists can tell where in the Laramie River the crayfish was introduced and observe how it has spread downstream.
“As they take hold, you see how the population shifts,” he said.
Anyone who finds a rusty crayfish should take a picture if possible and report the location by email to email@example.com or by calling the Laramie Ranger District at 307-745-4046. Reporting is mandatory within 48 hours of discovering an invasive species. A fine of up to $10,000 is possible for knowingly possessing one.
The department would prefer that the crayfish be killed, though that isn’t mandatory. The easiest way to kill one is to break it in half by separating the tail from the carapace.
The key to preventing the spread of such invasive species is to avoid moving them to new waters, which includes not bringing them home and not using them as bait.
“Either leave them there or kill them,” Compton said.
Landowners who are considering developing fishing ponds should be aware of the risk of introducing invasive species. Contractors should have a permit to deal in the species they supply. Wyoming Game and Fish Commission regulations prohibit importing rusty crayfish into the state.