Aquatic Invasive Species

Native to the Ohio River Valley, the rusty crayfish (Orconectes rusticus ) is an aquatic invasive species that has spread outside its native habitat into other freshwater sources ranging from Minnesota to Maine.  Detrimental to invaded ecosystems, rusty crayfish out-compete native crayfish and tend to replace the native crayfish population rather than just displace them. This out competition is mainly a result of the rusty crayfish’s larger body mass and greater reproductive abilities (Klocker and Strayer 2004). As rusty crayfish becomes more dominant with in an invaded environment, they can significantly reduce the amount of benthic invertebrates in an ecosystem resulting in the removal of much of the available nutrient resources in the water (Bobeldyk and Lamberti 2008). In addition the fish and bivalve population suffer under the invasion as rusty crayfish preys on small fish and the eggs of many species (Klocker and Strayer 2004).

Bait buckets are the main transport vector for rusty crayfish across state lines.  As the aquatic invasive species becomes a greater problem, programs have been developed to educate fishermen about the dangers of bait bucket transfer. However, this is not enough and the gravity of this problem has led Michael Potts of Duke University to investigate widespread control methods for rusty crayfish. A native of Pennsylvania, Potts became interested in rusty crayfish after discovering “a research article on the effect of the aquatic invasive species in [his] home state.”  As a result of this discovery, Potts proposes to study the effect of trapping and predation on rusty crayfish populations. Potts’ methodology draws upon a previous study conducted by Hein et al.(2006) in Wisconsin’s Sparkling Lake, however while both his and Hein et al.’s methodology are similar, Potts decided to focus his research on rusty crayfish population within dynamic water bodies, mainly rivers and streams, versus closed water bodies such as lakes. According to Potts, he took this focus “because not a lot of work has been done in moving waters (rivers) as far as trying to control rusty crayfish.”For the predation aspect of his proposal, he will use small mouth bass, a predator of rusty crayfish, and set up a control mechanism to maintain the bass’s population. He will then implement wire minnow traps along the river section in distances approximately 15 meters apart and bait it with frozen smelt and the sex, weight and length of captured specimen will be recorded.

While Hein et al.’s study differs from Potts. He stated in his proposal that “due to the similarities in lake and river ecosystems… it is hypothesized that the experiment will result in a significant decrease in rusty crayfish population.” Furthermore when asked about his believe in the future implication of his project, Potts stated that “ [the] methods in the proposal and the Hein et al (2006) study are very sound and could be easily replicated across different types of water systems such as  rivers, lakes, and steams and would significantly decrease the population of rusty crayfish.”

Sources:  Bobeldyk AM and Lamberti GA, Journal of Great Lakes Research. 34:265-275;  Hein CL, Roth BM, Ives RA, Vander Zanden MJ. Can. J. Fish. Aquat. Sci. 63:383-389.

Although small and seemingly harmless, crayfish of a certain species have invaded the streams of Pennsylvania, disturbing natural ecosystems. The species, named the “rusty” crayfish, has been accidentally introduced into Pennsylvania waterways and was found in the Little Juniata River in 2005, according to the Pennsylvania Outdoor News. Thousands of these crayfish were discovered by Bill Anderson below a hydoelectric dam at Warrior Ridge. Not native to Pennsylvania, rusty crayfish populations and infestations are extremely detrimental to both plant and animal life in Pennsylvanian aquatic environments.

According to the article, the “rusties” were likely introduced accidentally by fisherman through the vector of bait. Fishermen buy them unknowingly because of their similar features to the native crayfish, and the rusties then make it from the bait bucket to the water. They are native only to Indiana, Ohio, and Kentucky, but have invaded thirteen states in New England and the Midwest. Because of their aggressive nature, the rusty crayfish displace the normal native species in Pennsylvania waterways, completely destroying native populations. Animal life suffers in the streams as a result because rusty crayfish are not a high quality food source for the fish compared to the native crayfish. According to a crayfish researcher, David Lieb, the rusties also reduce plant abundance.

Measures are being taken to reduce the spread of rusty crayfish. Some states have banned the sale and use of rusty crayfish as bait, including Pennsylvania. Lieb believes that an education program and ban of rusty crayfish bait sales would reduce introductions of the species by ninety percent.

This seems to be a good effort to curb the spread of a dangerous species for delicate waterway ecosystems. It also striking that a species so similar to what already lives natively in Pennsylvania can cause such a disturbance. The impact could be wide-reaching, because if the reduction in food supply affects common game or edible fish, a decrease in Pennsylvania populations of these economical fish would reduce revenue in the restaurant sphere of business. I wonder what interactions between native species and the invading species of crayfish would look like. How do rusty populations increase so quickly?