The introduction of non-native species impacts our plant and animal communities, including local streams, lakes, and estuaries. There has been a lot of concern about the influence that nonnative crayfish are having on our waterways across Maryland.

Non-native crayfish
Credit: - Matt Sell

Introduced crayfish, such as the rusty crayfish and red swamp crayfish, have been transported into our region for use as fishing bait or as a food source in aquaculture. These crayfish are aggressive, eat a lot, grow quickly, have large claws, and tend to establish sizeable colonies.

Once large populations are established, these alien crayfish reduce biodiversity and affect the food web in our waterways. The rusty and red swamp crayfish are more aggressive than our native crayfish, often out-competing and decimating native crayfish populations.

Native crayfish have evolved within our local waterways and maintain a balance in the ecology and food web. The non-natives do not maintain this balance, and if large quantities of crayfish are present in a particular stream, it is most likely a non-native population. The voracious appetite of these alien crayfish also affects the aquatic clam, mussel, and insect communities which benefit water quality by filtering sediments and recycling nutrients through the course of their daily activities. As their populations are depleted, so are these important processes.

Stream surveys indicate that non-native crayfish reduce native mayfly and stonefly populations, as well, impacting local trout populations since these insects are a staple of trout diets. The fast growth of these non-natives also enables them to avoid being eaten by many fish that would normally feed on native crayfish, further creating an imbalance in the food web.

Large colonies of alien crayfish can also impact submerged aquatic vegetation — the plants that help aerate the water. Losing this vegetation reduces dissolved oxygen, which further degrades water quality. Some studies have also found that alien crayfish populations affect amphibian populations by consuming eggs and eating the young after they hatch.

The result of the overabundance of alien populations leads to a general degradation of water quality and overall stream health. A previous survey conducted in Maryland showed that populations of invasive crayfish are now established in the upper reaches of the Monocacy River and the Potomac River.

To avoid introducing alien crayfish, it is recommended that artificial crayfish baits be used for fishing and that crayfish are not moved from one waterway to another.

Article by FCFCDB

Nature Note for 3/12/2017