May: good fish, fun fish, bad fish, sunfish

Pumpkin sunfish. Photo: Simon-Pierre Barrett, from Wikimedia

Editor’s note: Dave Strayer Monthly articles help readers see their familiar world in new ways. He is a freshwater ecologist at the Cary Institute for Ecosystem Studies in New York.

Written by Dave Strayer

It might be a good time to search for sunfish’s nests. Sunfish build saucer-shaped nests (see photo below) a foot or two apart in the shallow waters of lakes, ponds, and rivers. Anxious males hover over nests, guard eggs and young, and chase intruders. Since the nests are often in very shallow water (sometimes almost on the shore), it is easy to see and watch.

The sunfish family includes some of Michigan’s most popular sport fish: largemouth and smallmouth bass, bluegills, pumpkin seed, crappie, rock bass and others. They are easy, fun to fish, attractive, good to eat, and very popular—almost every lake and warm river in the state contains sunfish. In Michigan and throughout the eastern United States, sunfish are among the highly valued freshwater fish.

Three pumpkin seed sunfishes (marked with arrows) guard their nests. Photo: modified by Fernando Alonso Vendrell, via Wikipedia.

It is also among the worst invasive fish species in the world.

Since sunfish are so highly valued in eastern North America, they have been extensively and indiscriminately stocked around the world for recreational fishing and released from aquariums into the wild. Anyone familiar with sunfish knows that it is an intelligent, curious, aggressive and adaptable fish, and speculates that it may have powerful effects on the ecosystems in which it is introduced.

In fact, they did.

The introduction of a largemouth bass bass into Lake Atitlan in Guatemala led to the extinction of a flightless exotic species by eating its food and chicks. In California, native fish “paid a heavy price” for the introduction of largemouth bass, green sunfish and other sunfish, helping drive many Californian native fish species to extinction or endangerment. In Europe, the introduction of pumpkin seeds has displaced native fish and reduced numbers of native invertebrates. Sure, some groups of sunfish introduced for fishing or food are valued, but almost all sunfish introduced to Europe are considered pests, and largemouth bass is on the list of the world’s 100 worst invasive species.

Sunfish are among a very long list of invasive species that are valued in their native ranges but cause problems and are scorned when introduced. European rabbits are valued as food, pets, and things of affection (think Peter Rabbit) in Europe, but they have caused massive damage to local wildlife and grasslands in Australia. Black cherries are valued for timber and wildlife foods in North America, but are ranked as one of the worst invasive species in Europe. Asian carp are valued as a food fish in China, but are seen as an existential threat to fisheries in the Great Lakes region and elsewhere in North America.

We spend a lot of time and energy arguing about whether these species are good or bad. People who want to control species in conquered areas often describe them as evil, sometimes in frightening terms (for example, “Frankfish”, “Plant from Hell”, “Plant vampires”, “Killing wasps”). Opponents of control often counter by calling the species good, citing their value in their native land. The purpose of such images is to justify management actions: evil species must be destroyed, while good species must be protected or even propagated.

But as the sunfish example shows, it is not easy to categorize the species as good or bad. The sunfish is highly valued in the eastern United States and causes severe damage elsewhere. With a few exceptions (for example, mosquitoes that carry diseases dangerous to humans), it is simply difficult to classify the species into good and evil from a human point of view. Attempts at such a simple categorization are more likely to lead to heated and deadlocked discussions rather than provide a useful guide to management.

Additionally, focusing on whether a species is good or bad distracts us from the central problem of invasive species management, the indifferent movement of species around the world by people. Responsibility for problems with invasive species lies with the people moving the species around, not the “bad” species. It’s not that the sunfish is essentially a good or bad fish, but that people have moved sunfish everywhere without thinking about the consequences.

It turns out that the consequences of moving a species into a new ecosystem are difficult to predict, which can be large and long-term. In fact, invasion biologists do not yet know whether accurate predictions can be made. At the very least, they will need careful analysis by smart people.

Dave Strayer

But we know that the man who stored largemouth bass in Lake Atitlan wasn’t smart enough, nor was he the aquarist who shot pumpkin seeds in France. Thomas Austin, the man who brought rabbits to Australia, wrote “Introducing a few rabbits can do a little harm and may provide a touch of home,” was not smart enough. Etienne Leopold Trouvelt, who brought what were called “gypsy moths” to North America, wasn’t smart enough.

I’m not smart enough, and maybe I’m not. And people who want to introduce genetically modified counterparts to extinct animals like woolly mammoths and riding pigeons haven’t shown us that they are smart enough to predict the outcome of these introductions either.

So, by all means, go out and see the beautiful and fun sunfish in their nests this month. If you are so inclined, go sunfish and enjoy this delicious fish on your plate. But please, please, don’t move them or any of Michigan’s beautiful and interesting flora and fauna into a new ecosystem.

You are not smart enough.

Other articles in this series:

January: Ice Kingdom

February: the death of winter

March: stormy weather

April: hidden migrations

May: good fish, fun fish, bad fish, sunfish

June: The toughest month?

July: keep calm

August: Molasses on the water

September: Etisalat

October: Scents of Autumn

November: What’s Thanksgiving Dinner for?

December: Visit the Ice Museum

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