Aquatic Invasive Species: It’s Complicated

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An Asian Carp jumping. Photo used with permission from Michigan Sea Grant.

Shedd Aquarium was my first job. As part of the "Teen Work Study" program, I learned about different types of marine animals such as turtles and stingrays. Additionally, I found out about the conservation and research teams that help animals in the wild. For example, there is a Great Lakes conservation team who study creatures in our local waterways. And part of my job was sharing these animals and information with visitors.

When speaking with aquarium guests, I found some people are often confused about the difference between an invasive species and a non-native species. Non-native species are animals from foreign places that have found their way into new ecosystems. Many animals migrate to new areas for survival purposes with no intention to harm native inhabitants. But if a non-native species damages the local ecosystem, then it is classified as an invasive species. It is the whole ‘all squares are rectangles, but not all rectangles are squares’ thing.

Invasive species are animals non-native to the ecosystem and cause environmental harm. It can be hard to define if an animal is helping or hurting its adopted ecosystem, though. In some cases, there are potential benefits of invasive species. Some non-native plants and animals consume species that we consider pests or provide new habitat for endangered birds. For instance, many native butterflies in California feed on and benefit from non-native plants. These plants may have damaging effects on other plants in the area, however. If the adverse effects outweigh the positive effects, the species is considered invasive.

This precarious balance can change over time, too. An invasive species can be helpful to its non-native habitat when they arrive, but later become overgrown or problematic. Let’s take Asian carp as an example. Asian carp are filter feeders; they eat plankton and algae. They grow about 4-5 feet long and eat 20% of their body weight daily. They also reproduce quickly.

Humans brought Asian carp to the United States for algae control in aquaculture and farm ponds in the 1970s. But a flood season in the 1980s helped the carp escape into the wild. They made their way to the Mississippi River with the aid of human-made canals and fishers. (Asian carp can jump high out of the water and be trapped or stowed away on fishing boats.) Consequently, carp have invaded many lakes and rivers across the country. (So far, researchers haven’t found any Asian carp DNA in the Great Lakes and electrical fences have been set up to block further expansion, but it is certainly not a perfect solution.)

Now out in the wild rivers and streams of America, these fish need so much plankton that there is little left for other indigenous fish. In many areas, it has become a competition for resources, which threatens the livelihood of local wildlife. 

So what can we do about this accidental fish invasion? An easy solution would be to eat them! People think carp tastes bad because they are bottom feeders and, in North America, people find them too bony to filet. But in some Asian countries, carp have been a source of food since ancient times. Bighead carp soup is considered a delicacy in countries like China. They are a rich source of Omega 3’s and tasty! Some people here in the Midwest are trying to make carp into human food while others have used them to create dog treats. Finding a way to make carp delicious and appealing here in America may help us reduce the growing invasive population.

Asian carp often get a bad rap, as though they are the villains in our waterways. But let’s remember they only behave according to their basic survival instincts, just like us. It is not their fault they ended up in our waterways. People brought them to America. Human-made canals helped them spread to so many places. These fish are just eating to survive, and they need a lot of food to do so. I am not defending the fact that they harm their new environments in the US. There is a lot we need to do to protect our waterways from risks like these. But these fish were never villains. From what I learned at Shedd Aquarium, each animal has its own story.

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