Aquatic Invasive Species

An experiment on biological and mechanical control across an entire lake showed that taken together, the two types of control can effectively reduce rusty crayfish populations.

Catherine Hein and her colleagues from the Department of Limnology at University of Wisconsin explored potential for rusty crayfish control by trapping adult crayfish and limiting fishing to increase bass populations in Sparkling Lake. They found that the combined control method significantly reduced the invasive crayfish population, removing an estimated 1,212,148 specimens in a three year period from 2001 to 2003.

From the results of the study, Hein et al. concluded that taken together, predation and trapping can effectively remove and control established populations of the invasive species Orconectes rusticus, and should continue to be considered as a method of management.

Can. J. Fish. Aquat. Sci. 63: 383–39, 2006.

Prized as one of the traditional culinary dishes of New Orleans, the red swamp crayfish (Procambarus clarkii) has a very different meaning in Italy. After being introduced in the 1970s, the red swamp crayfish has proven to be one of the most successful invasive species in Italian freshwater environments. Annalisa Paglianti and Francesca Gherardi from the University of Florence in a recent study compared the growth of both the native crayfish (Austrioitamobius pallipes) and the red swamp crayfish with respect to temperature and food diet. They found that the in increased temperatures, an increasingly more common characteristic in Europe, the red swamp crayfish grew at a significantly faster rate than the native species. They also found that identical diets produced faster and larger growth in the red swamp crayfish. These findings have led scientists to theorize that the success of the red swamp crayfish in Italy may be due to these characteristic. However, this theory represents only a small portion of the complex interaction of the red swamp crayfish in Italy.

Journal of Crustacean Biology. 2004. doi: 10.1651/c-2374

An evaluation of the effects of rusty crayfish on a stream ecosystem showed that the crayfish have not been found further downstream than they had been found in a previous study of crayfish distribution and expansion.

Bobeldyk and Lamberti of the Department of Biological Sciences at the University of Notre Dame conducted a longitudinal survey of the spread, density, and effects of an invasive crayfish species downstream of Bond Falls in the Middle Branch of the Ontonagon River and compared the results to a similar study completed in 1992. Using a 28 day leaf breakdown experiment, Bobeldyk and Lamberti sampled benthic substrates in three areas of different expected crayfish density. The study’s findings demonstrate that the crayfish have not expanded downriver and have in fact been found less far downriver than in 1992.

Bobeldyk and Lamberti concluded based on the leaf breakdown experiment that while the crayfish did not spread, they significantly reduced available stream resources wherever they were found.

J. Great Lakes Res. doi: 10.3394/0380-1330(2008)34[265:ADAIET]2.0.CO;2 (2008).

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?