Claws for Alarm

Many Missouri stream and lake enthusiasts may be unaware of an invasion that threatens the aquatic resources that we love.

While most of us understand the danger posed to our aquatic environments by foreign invaders such as zebra mussels and Asian carp, it is harder to wrap our minds around the idea that crayfish, a key component of Missouri’s stream and lake fisheries, are also invading and threatening our waterways. But it’s happening, it’s a serious problem, and anglers and other aquatic enthusiasts should be concerned about this threat.

Upstanding Residents

Invasive species are now the second most important problem facing biologists who manage aquatic ecosystems in the United States (U.S.), right after habitat loss. Aquatic invaders are the threat that keeps fisheries managers awake at night.

Crayfish (also known as crawfish and crawdads) are among the most important prey for many Missouri sport fish. Research shows what many anglers already know — crayfish provide fuel for catfishes, trout, and walleye, and they compose most of the diets of popular species such as smallmouth bass, goggle-eye, and adult largemouth bass.

However, few people understand that crayfish play other critical ecological roles in our streams, lakes, and wetlands. Crayfish feed more than 200 wildlife species that live in and around our waterways. Their omnivorous diets (they eat nearly everything) and intense predation allow them to partially control the kinds and abundance of plants and other animals (fish food such as insects and snails) in these ecosystems. Their constant work breaking down dead and decaying plants into food for other animals drives food chains and nutrient cycles. They can affect water clarity when over-abundant. In short, crayfish play an unusually important or keystone ecological role in many fisheries and aquatic environments due to their ability to alter food chains and their environment.

Out-of-towners

So how does an organism with so many beneficial traits become a problem? First, understand that while we mostly hear about a few crayfish species, such as the infamous and highly invasive rusty crayfish, there are actually more than 400 crayfish species in North America. Many have small native ranges where, over many thousands of years, they have established a balance with the plants and other animals in their environment. But when a crayfish species is moved out of its native range to unfamiliar streams and lakes, even if they are nearby, we can’t predict how it will interact with