Invasive Watchlist | Chinese Mitten Crab

The Chinese mitten crab may pose serious threats to the future of fishing in Michigan if precautions aren’t taken; though the species technically hasn’t been detected in Michigan yet there have been few reports of it making its way into the Detroit River as well as one caught in Lake Erie, back in 2007.  

The mitten crab is a catadromous species, which means it is born in a marine environment, and migrates to freshwater to live, then migrates back to a marine ecosystem to breed.  With sightings in the Mississippi River, local concerns have developed in Michigan as the mitten crabs continue to migrate closer and closer to the Great Lakes Region.  Within freshwater systems, mitten crabs can be found in rivers, streams, estuaries, or bays that are abundant in aquatic vegetation, according to MDNR. 

Within those freshwater systems, the mitten crab has a wide and aggressive diet, consuming detritus, aquatic plants, algae, benthic invertebrates, and even salmon, trout, and sturgeon eggs.  This appetite can completely alter a food web, and may allow the mitten crab to outcompete native crabs, crayfish, and mussels for resources, according to Midwest Invasive Species Information Network (MISIN).  The mitten crabs burrowing behavior can also have a significant impact on stream bank stability, and can increase erosion.  Not to mention the mitten crab can consume fishing bait, damage or consume fisherman’s catch, as well as damage fishing nets, clog pumps, screens, and water intake structures, making them a fisherman’s nightmare.  They could have significant impacts on the fishing industry as well general recreation out on the waterways if they were to make their way into the Great Mitten State.

Identifying a Chinese mitten crab is fairly easy; they tend to be a brownish-orange to greenish-brown in color, their claws are covered in hairs and the tips are white, giving it the mitten look.  They have a convex and uneven shell that reaches the size of an adult palm, and they also have a notch between their eyes and 4 spines on each side of the carapace (the hard upper shell).

The distribution and introduction from their native regions of Korea and the pacific coast of China is most likely due to ballast water and possibly through intentional release, which may due to its traditional food source in China, where it supports a large aquaculture industry.  Being introduced into a new environment is dangerous since they tolerate a wide range of conditions and can spread wide and fast. 

The Chinese mitten crab is currently the only crab found in fresh waters in North America, so let’s keep it that way and help prevent the spread of these aquatic nuisances from reaching further territories and altering our fresh water ecosystems which are an integral part of Michigan culture and history.  With fresh water on the mind, remember to always clean your boats, gear, trailers and so forth before switching water bodies, keeping the Great Lakes clear of aquatic nuisances is becoming more and more essential as we fight to protect our native species and outdoor heritage!

This article is part of the ongoing series on invasive species funded in part with funds from the Michigan Invasive Species Grant Program through the Departments of Natural Resources, Environmental Quality, and Agriculture and Rural Development

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