Aquatic Invasive Species

Rusty Crayfish

First discovered in 1960 in a Minnesota lake, Rusty Crayfish have since spread to lakes in over seventeen states in the United States Midwest and parts of Canada. The fact that these Rusty Crayfish are not originally native to these Midwestern lakes creates quite an unsavory predicament for the native marine life, mostly due to the Rusty Crawfish’ aggressive invasion tendencies. Rusty Crayfish tend to displace other native crayfish species, but they also harm native fish populations by feeding on their unhatched eggs which lie at the bottom of the lakes. Finally, these pesky crustaceans also severely reduce the amount of aquatic vegetation in lakes.

Although not confirmed, the spread of Rusty Crayfish is believed to be linked with careless anglers who dump their bait buckets or do not pay attention to what live bait they are using. Even transferring only a few Rusty Crayfish can be detrimental to a lake’s ecosystem, since females can carry both fertilized eggs and male sperm. This means that feasibly all that is needed to start a new population of Rusty crawfish is a single female. There have been attempts however, to regulate this spread stemming from when the species was declared a regulated invasive species, simply meaning that the spread of Rusty Crayfish into the wild is illegal.

Although Rusty Crayfish are very harmful to native Midwestern lake ecosystems, many strides have been made in legislature to control the population. Starting with declaring Rusty Crayfish to be an official regulated invasive species, it is now illegal to spread Rusty Crayfish into the wild and even simply sell them as live bait. Of course, some penny-pinching fisherman will still inevitably opt to use live Rusty Crawfish as bait, which is why it would probably be a good idea to start cracking down on the bait industry to make sure all live bait is regulated and Rusty Crawfish-free. In terms of getting rid of the current infestation of Rusty Crawfish inhabiting lakes, a few options are available. Some suggest the use of chemicals to kill the invader, but nothing has yet been discovered that kills the Rusty Crayfish that doesn’t also kill native crawfish as well. Interestingly enough, it was once actually proposed to use the invasive Rusty Crawfish to regulate the population of the also invasive Eurasian Watermillfoil, but this idea was swiftly turned down. The best option, it seems, would be to ask fishermen to use Rusty Crawfish in lakes where they have already established a home in as bait whenever possible. While this method will definitely not eradicate the population, it will surely prove to be damage-control at the very least, most likely protecting many native aquatic plants and animals.

Sources

http://www.dnr.state.mn.us/invasives/aquaticanimals/rustycrayfish/index.html

http://www.seagrant.umn.edu/ais/rustycrayfish

http://www.seagrant.umn.edu/ais/rustycrayfish_invader

Reading the four articles, especially the Mute Swans article, got me thinking about the definition of invasive species. While the ecological definition of invasive species is relatively well defined (“non-native species of plants or animals that out-compete native species in a specific habitat” from http://www.floridasprings.org/glossary.html), I feel that that the qualities that label a species as “invasive” and offensive by the public are much more vague.

The Mute Swans, for example, are scientifically an invasive species. The species was first introduced to the East Coast from Europe and Asia in the early 1900’s, when they were imported as decorative birds for parks and estates. Wild Mute Swan populations increased drastically in the Chesapeake Bay in the 1980’s and 90’s, as they out-competed native species for food and habitat. Legislation was passed in 2000 to control the swan population. There has, however, been public opposition to killing the mute swans. The article from class mentioned the “deeply divided” state panel, and the opposition from animal rights groups.

Mute swans pose just as great a threat to native species as snakeheads or didymo, but the opposition to swan population control in the Chesapeake made me wonder why there were no similar movements for these species. I guess the fact that swans are more aesthetically pleasing (as opposed to http://www.mountainmurmur.com/wp-content/uploads/2008/11/didymo-mararoa_s1.jpg) does influence public opinion on how comparatively “invasive” species seem, since noone wants didymo in their water. I’m sure there are many other invasive species that drastically disrupt native ecosystems and completely drive away certain species, but we don’t make a big deal about them because we are okay with having the invasive species around. There are factors (economic or aesthetic) other than endangering native ecosystems that the public takes into account when we decide whether a species is “invasive” and should be eliminated, or if nature should be allowed to run its course.

http://news.nationalgeographic.com/news/2003/06/0605_030605_muteswan.html

http://www.chesapeakebay.net/muteswan.aspx?menuitem=16930

Eurasian Watermilfoil has been crowding out species native to the Americas for some time now; its estimated introduction to our continent is 1900. Its introduction may have been caused by its survival in a boats ballast water or the aquarium trade, and its spread is significant due to its reproduction through stem fragmentation. A colony of watermilfoil gets tangled on boat, and stems of the plant are consequently transported.

This invasive species out competes native flora, causing an imbalance in the natural lake ecosystems throughout America. Specifically, watermilfoil tends to dominate nutrient-rich lakes, having less of an impact on ones lower in nutrients. Watermilfoil threatens such ecosystems by dominating the lake surface and encroaching its shallows. This is certainly concern for the native flora, but as for us, the nuisance of thick, ugly vegetation is its only imposition. Therefore, the question is whether the removal or containment of eurasian watermilfoil is worth the money it costs, whether it is our duty to protect the native species.

http://www.invasivespeciesinfo.gov/aquatics/watermilfoil.shtml

http://www.great-lakes.net/envt/flora-fauna/invasive/milfoil.html