Wednesday, March 30, 2011

Know the Enemy (Third in a Series)

Rusty Crayfish (Orconectes rusticus)

These little critters are virtually everywhere in Wisconsin, but are the most plentiful in Oneida and Vilas Counties.
It may take an expert to distinguish 'rusties' from native species, but the impact is almost surely noticeable.  Rusty crayfish are voracious plant eaters, so a lake may experience a reduction in plant life, reducing cover for fish, spawning grounds and food.  Rusty crayfish have also been known to eat fish eggs.  Fish that normally eat native crayfish, don't like the 'feisty' rusty crayfish.

They are aggressive and displace native crayfish. Rusty crayfish are prolific; females lay from 80-575 eggs!

These little invasives prefer to live in areas with cobble, rocks, logs, or other debris.  For cover, bottom types may be clay, silt, sand, gravel, or rock.

Rusties are so aggressive they may alter the ecosystem of a lake.

This species is so prolific that it has been deemed impossible to eradicate.  Introduction of one female to a body of water in the right conditions may cause an infestation.

How are they best controlled?  Read Fish Predation and Trapping for Rusty Crayfish Control on Plum and Star Lakes: A Commentary by Frank G. Splitt of Vilas County. 

For further information click here.

Tuesday, March 1, 2011

Know the Enemy (Second in a Series)

Eurasian water milfoil is a submersed aquatic plant native to Europe, Asia, and northern Africa. It is the only non-native milfoil in Wisconsin. Like the native milfoils, the Eurasian variety has slender stems whorled by submersed feathery leaves and tiny flowers produced above the water surface. The flowers are located in the axis of the floral bracts, and are either four-petaled or without petals. The leaves are threadlike, typically uniform in diameter, and aggregated into a submersed terminal spike. The stem thickens below the inflorescence and doubles its width further down, often curving to lie parallel with the water surface. The fruits are four-jointed nut-like bodies. Without flowers or fruits, Eurasian water milfoil is nearly impossible to distinguish from Northern water milfoil. Eurasian water milfoil has 9-21 pairs of leaflets per leaf, while Northern milfoil typically has 7-11 pairs of leaflets. Coontail is often mistaken for the milfoils, but does not have individual leaflets.

NOTE:  This invasive's existence was confirmed in the upper Wisconsin River, near the Rainbow Flowage in 2005.

Source:  Wisconsin Department of Natural Resources (click here for further information)