Editor’s note: by Dave Strayer monthly essays help readers see their familiar world from a new perspective. He is a freshwater ecologist at the Cary Institute of Ecosystem Studies in New York.

By Dave Strayer

May is a good time to look for sunfish nests. Sunfish build saucer-shaped nests (see photo below) a foot or two in diameter in the shallow waters of lakes, ponds, and rivers. Anxious males hover over nests, guarding eggs and hatchlings, chasing intruders. Because the nests are often in very shallow water (sometimes almost on the shore), they are easy to see and observe.

The sunfish family includes some of Michigan’s most popular sport fish: large and smallmouth bass, bluegill, pumpkinseed, crappie, bass and others. They’re easy and fun to catch, attractive, good to eat, and very common – nearly every warm lake and river in the state has sunfish. In Michigan and throughout the eastern United States, sunfish are among the most popular freshwater fish.

Three pumpkinseeds (marked with arrows) guarding their nests. Image: Modified from Fernando Alonso Vendrell, via Wikipedia.

They are also among the worst invasive fish species in the world.

Because sunfish are highly valued in eastern North America, they have been widely and indiscriminately stocked all over the world for recreational fishing and released from aquariums into the wild. Anyone familiar with sunfish knows that they are intelligent, curious, aggressive and adaptable fish, and would predict that they could have strong impacts on the ecosystems into which they are introduced.

Indeed they have.

Largemouth bass introduced to Lake Atitlan, Guatemala, drove a species of flightless grebe to extinction by eating its food and chicks. In California, “native fish have paid dearly” for the introduction of largemouth bass, green bass and other sunfish, contributing to the extinction or endangerment of several fish species natives of California. In Europe, introduced pumpkin seeds have displaced native fish and reduced native invertebrate populations. Granted, some introduced populations of sunfish are prized for angling or food, but nearly all introduced sunfish in Europe are considered pests, and largemouth bass is on the list of the 100 worst invasive species in the world. world.

Sunfish are one of the very long list of invasive species that are loved in their native ranges, but cause problems and are reviled where they have been introduced. European rabbits are valued as food, pets and objects of affection (think Peter Rabbit) in Europe, but have caused immense damage to native wildlife and rangelands in Australia. The black cherry is valued for timber and wildlife food in North America, but is ranked as one of the worst invasive species in Europe. Asian carp are considered a food fish in China, but considered an existential threat to fisheries in the Great Lakes and elsewhere in North America.

We spend a lot of time and energy discussing whether these species are good or bad. People who want to control species in invaded regions often describe them as evil, sometimes in grim terms (e.g., “sharp fish”, “hell plant”, “vegetable vampires”, “murder hornets”). Opponents of control often counter by describing the species as good, emphasizing their value in their native land. The intention of such representations is to justify management actions: bad species should be destroyed, while good species should be protected or even propagated.

But as the example of the sunfish shows, it is not straightforward to categorize species as good or bad. Bluegills are popular in the eastern United States and cause serious damage elsewhere. With a few exceptions (eg, mosquitoes carrying serious human diseases), it is difficult to simply rank species between good and bad from a human perspective. Attempts at such a simple classification are more likely to lead to heated and dead-end debates than to provide a useful guide to management.

Additionally, focusing on whether a species is good or bad diverts our attention from the central problem of invasive species management, which is the reckless movement of species around the world by humans. The blame for invasive species problems rests with the people who moved a species, not the “bad” species. It’s not that sunfish are inherently good or bad fish, but that people have moved sunfish all over the place with barely a thought of the consequences.

It is difficult to predict the consequences of moving a species into a new ecosystem, which may be large and long-lasting. In fact, invasion biologists don’t yet know if accurate predictions can be made. At least they will require careful analysis by smart people.

Dave Strayer

But we know the guy who stocked largemouth bass in Lake Atitlan wasn’t smart enough, nor was the aquarist who introduced pumpkin seeds to France. Thomas Austin, the man who brought rabbits to Australia and wrote “The introduction of a few rabbits might do little harm and might give a touch of home”, was not smart enough. Étienne Léopold Trouvelot, who brought what used to be called “spongy moths” to North America, was not smart enough.

I’m not smart enough, and you probably aren’t either. And people who want to introduce genetically engineered analogues of extinct animals like woolly mammoths and passenger pigeons haven’t shown us that they’re smart enough to predict the outcomes of those introductions either.

So, by all means, get out and watch our beautiful and interesting sunfish on their nests this month. If you feel like it, go panfish fishing and enjoy these delicious fish on your plate. But please, please don’t move them, or any of Michigan’s beautiful and interesting plants and animals, into a new ecosystem.

You are not smart enough.

Other essays in this series:

January: The Ice Kingdom

February: The Heart of Winter

March: Stormy weather

April: hidden migrations

May: Good Fish, Fun Fish, Bad Fish, Sunfish

June: The cruellest month?

July: stay cool

August: Dibs on the water

September: Connections

October: The smells of autumn

November: What’s for Thanksgiving Dinner?

December: A visit to the Ice Museum