I recently came across a pair of posters on a tree by the Potomac’s C&O Canal at Riley’s Lock. The upper poster shows the familiar largemouth bass and warns any fisherman catching one to release it immediately.

The lower poster, solidly fastened with anti-rust screws, depicts a creature with a small head, boldly patterned body, and fins that run along its top and bottom. It looks like a fish that could have swam with the plesiosaurs, certainly unlike anything ever seen in this part of the Potomac. It’s called the snakehead.

“Have you seen this fish?” the poster wants to know. It goes on to demand that if you do catch one, you must act immediately. “PLEASE DO NOT RELEASE,” the poster says. “Please KILL this fish by cutting/bleeding or freezing.”

Why does the Maryland Department of Natural resources want us to protect one fish and execute the second, no questions asked? The poster tell us. The snakehead comes from China. As a non-native, it will out-compete the Potomac’s natives and upset the river’s ecosystem. And the bass? This fish is the icon of the Potomac with a lineage that surely stretches back into the river’s misty past.

Except for one thing. Bass are not native to the Potomac either. Largemouth bass come from the southern US, and smallmouths from the Ohio Valley. What’s more, nearly all of the Potomac’s other fish that people know and love also came from somewhere else.

I took another look at the two posters. They’re not really about two fish, I concluded, one good, the other bad. The posters actually are about us.

Environmental heresy. Downstream from Riley’s Lock, not far from where the tidal Potomac runs past Washington, D.C., the American Association for the Advancement of Science was holding its annual meeting. Speaking at one session was Mark Davis, a biologist and expert on invasive species. Maybe he would clear up the paradox of the two posters.

Davis told the audience that in his view, much of the scientific-sounding debate over non-native, so-called invasive species, has little to do with science. Instead, it has a lot to do with personal belief and a kind of biological jingoism.

“Groups in society have different values,” he said, “and may come to different conclusions with respect to different species and the harm, change, or even benefits they cause.”

Yes, but what about snakeheads? Shouldn’t we be worried that such a fish could destroy our healthy Potomac River ecosystem?

This is how Davis put it:  “There’s no such thing as healthy ecosystem. When we refer to a healthy ecosystem, we’re talking about how we want the ecosystem to be.” Following this line of reasoning, invasives such as the snakehead admittedly do affect ecosystems. But the key point, according to Davis, is that some of the changes we like and others we don’t. It’s all about us.

You would think that evidence-based science would solve the matter of what’s good and what’s bad. But according to Davis, many scientists themselves are responsible for distorting the issue. “Scientists influence the decision-making environment by influencing the ‘valuescape,’” he said.  Take the statement, “genes from invasive species contaminate native gene pools.” This is what Davis could call hybrid language―seemingly scientific, but containing a hidden element of value judgment, in this case the loaded word “contaminate.”

“When we declare something as invasive and harmful,” he continued, “we oblige society to take action. ‘Get out chemicals, trample other plants, spray, spray, spray!’”

Borers and beetles. That said, Davis perfectly accepts the need to combat pest species—non-native or otherwise—when they threaten our health and safety or negatively impact ecosystem services on which we depend. “It comes down to change versus harm,” he said.

For example, the emerald ash borer is killing ash trees throughout North America. It originally comes from Asia. The mountain pine beetle is devastating pine trees across Western North America. But this second bug is a native. Which is worse?

In some cases the “valuescape” contains “facts” that seemingly come out of nowhere. For example, even respected authorities perpetuate the notion that invasive species are the world’s second greatest extinction threat (after habitat destruction). “This is cited thousands of times,” said Davis, adding that it is “sometimes not even cited, just repeated as fact.” He noted that this “fact” originated in a scientific article by a respected ecologist at Princeton. The article itself didn’t rank extinction threats, but instead merely reported on what people thought were threats. In fact, the article stated that its conclusions were based on little or no empirical data.

Attitude management. The reason the snakehead ended up on the wanted poster may be because our attitudes about invasive species were formed in previous generations, said Davis. The proponents of these attitudes today are typically people in their later years.

“Kids are now growing up in a completely globalizing world, surrounded by people and cultures from all over, he continued.” Davis advised that rather than trying to manage new species, we should be learning to manage our attitudes towards them.

In addition there are the high costs of insisting on our beliefs. “We simply don’t have the money to eradicate every species we don’t like,” Davis said, “even if we could.”

“And we certainly don’t have the luxury to use public money to fund personal preference,” he added. “We should reserve our resources to try to eliminate species that threaten human health or cause economic harm,” he said.

Given all of this, it seems ironic that public money is even now being spent on helping  non-native species get a finhold in the Potomac. Among them are the muskellunge, walleye, and rainbow trout. In the Potomac, many of our most beloved fish got here because people (and government agencies) believed that they provide better sport or better eating than the natives.

Maybe so. Certainly an introduced bass is more fun to catch than a native white sucker. But how about rolled in breadcrumbs and baked? From the culinary reports I’ve read, this honor must surely go to the snakehead.