Animal Invasive Species

Zebra and Quagga Mussels

Zebra and quagga mussels are a serious threat to Colorado waters. Invasive species such as the zebra mussel negatively influence the food chain for native fish. Zebra mussels remove major quantities of phytoplankton from the water. Phytoplankton is food for larval and juvenile fish. To learn more about the negative affects of aquatic nuisance species, visit 100th Meridian Initiative and Protect Your Waters.

To help prevent the spread of zebra and quagga mussels, boaters should remember to follow these steps: Clean, Drain, Dry.

Check your boat and trailer every time before you transport your boat. Overland transport of boats, motors, trailers and other watercraft poses the greatest risk for spreading zebra and quagga mussels. Adult mussels can attach or “hitchhike” to any surface and can live several days out of water (depending on the time of year) in moist, shaded areas. The microscopic mussel larvae (known as veligers) can be transferred in water contained in live wells, bilge, ballast tanks or “minnow” buckets. Check out these educational catchy tunes that offer listeners tips on preventing the spread of aquatic invasive species.

For more information on this topic, click here to connect to the Colorado Division of Wildlife website.

To help the Colorado Division of Wildlife quickly identify new populations of this unwanted species please report any sightings to Elizabeth Brown, Invasive Species Coordinator, 303.291.7362.

Rusty Crayfish (Orconectes rusticus)

This species, which is native to the Ohio River basin, can often be identified by two rust colored marks on its mid-back area, near the area where one would place a thumb and finger to pick the animal up. Adults reach a maximum length of four inches. Original spread was by anglers using rusty crayfish as bait, but the crayfish were also harvested for regional bait markets and for biological supply companies, activities which probably helped spread the species further.

Rusty crayfish inhabit lakes, ponds, and both pool and fast-water areas of streams, which makes many areas in Colorado potentially suitable habitat. They are opportunistic feeders and will eat a variety of aquatic plants, benthic invertebrates (like aquatic worms, snails, leeches, clams, and aquatic insects), decaying plants and animals, bacteria and fungi, fish eggs, and small fish. Rusty crayfish cause a variety of negative impacts when introduced to new waters, including displacing native animals and plants.

For more information on this topic, click here to connect to the Colorado Division of Wildlife website.

New Zealand mudsnail (Potamopyrgus antipodarum)

This small aquatic snail is native to freshwater lakes and streams of New Zealand. In the United States, this snail was first detected in the mid-1980s in the Snake River region of Idaho. Since then, it has spread to waters of Montana, Wyoming, Colorado, California, Arizona, Oregon, and Utah. Mature New Zealand mudsnails average 1⁄8 inch in length and have brown or black cone-shaped shells with five whorls. One way to identify this species is hold the point of the shell upward. Unlike snails native to Colorado, when the point of the shell is facing up, the shell’s opening is on the right.

The mudsnail attaches to fishing gear, boats, trailers, or even fish and bait, and then comes off in the next stream or river where these things are used or discarded. Mudsnails are able to close their openings to withstand dry conditions and a variety of temperatures. They can survive out of water for several days, so it's easy to see how they can move about and survive on recreational gear. Mudsnails consume aquatic vegetation, upsetting the balance of the aquatic environment. They reproduce asexually; it only takes one to start a whole new population! Eradicating established infestations is impossible.

For more information on this topic, click here to connect to the Colorado Division of Wildlife website.

Spiny Water Flea (Daphnia lumholtzii) & Fishhook Water Flea (Cercopagis pengoi)

Spiny and fishhook water fleas are small predacious crustaceans—a group of animals that includes crabs, shrimp, crayfish, and lobsters. Unlike these other crustaceans, the spiny and fishhook water fleas are very small creatures known as zooplankton. Both arrived in ship’s ballast water from Eurasia.

Water fleas threaten aquatic ecosystems and fishing by competing with native fish for food and fouling gear. Both water fleas eat smaller zooplankton that is important food for juvenile fish. With less zooplankton to feed on algae, algal populations can bloom, making lake water less clear. Even though these waterfleas can be eaten by fish, their spine deters most small fish, which experience great difficulty swallowing the water fleas.

Waterfleas collect in masses on fishing lines and downrigger cables. The buildup is so heavy that it becomes nearly impossible to fish with any degree of enjoyment. Water fleas can spread to inland waters when recreational gear is contaminated with egg-laden females. While females die out of water, under certain conditions they produce eggs that resist drying, remain viable, and can establish a new population. Eradicating established infestations is impossible.