The kids were intelligent, inquisitive, and way ahead of me on the issues of sustainability. When Hall-Dale teacher Bob Sinclair invited me to speak to his class of juniors and seniors studying sustainability, I was very pleased.

The hour went quickly, as we discussed a host of issues from forests to wildlife to commercial and recreational fisheries to exotic animals to invasive species to climate change to energy to — well, you get the idea. I began by asking them if managing all species sustainably was always a good thing. Thought I’d surprise them on this one. But they already knew the answer is no.

We’ve made many mistakes with our management of the nation’s natural resources, no more so than with fisheries. So I started there, with rainbow trout. Using Anders Halverson’s book, “An Entirely Synthetic Fish,” as my guide, I told the students that 100 million quarter-pound rainbows are stocked each year in the United States.

In state after state, the allure of rainbows drove anglers and fisheries managers to toss aside native species in favor of the fish that grows fast, jumps out of the water when hooked, and is easy to catch.

“In what I’d call Death on the Green River,” wrote Alverson, “in September of 1962, 450 tons of fish and aquatic invertebrates were poisoned. The Green River and its tributaries were virtually devoid of visible life, an ecological clean slate. The operation, in other words, was a complete success.”

The government poisoned all the fish in one of the biggest watersheds in the West, risking extinction for many of the river’s native species so it could stock rainbow trout. Four of the species killed in that operation ended up on the federal Endangered Species List. We have spent more than $100 million so far trying to save those four species from extinction.

Well, I told the students, we make these decisions daily, picking and choosing which native species to save, and which to let go in favor of newer “better” species. Most of the time we cannot anticipate the consequences of our actions.

We talked about what a small world we live in today. One of the consequences is the arrival in Maine of many invasive species, from the green crabs that are wiping out mussels and clams to the fungi that has killed 97 percent of the brown bats in the northeastern United States.

When I asked them if Maine has more or less trees than we had 100 years ago, they said less — the answer I would expect from most Mainers. But the answer is more. A lot more. So I was able to teach them something!

We considered the potential impacts of climate change, the ethics and consequences of fiddling with genetics, the threats posed by exotic species in our state, and the potential of energy independence for Maine. We all agreed that wind, water and wood could make that possible. I told them it would be up to their generation to make that happen.

My hour went by fast, but it was when I stayed for the second hour of the class that my eyes were really opened.

The subject was “a case study examining mercury bioaccumulation and biomagnification.” A narrative offered a story of a pregnant woman who, at lunch with a friend, was debating the possibility of eating tuna. The pregnant woman had been told she shouldn’t eat certain types of fish more than once or twice a week and thought tuna might be on that list.

This was something I knew a bit about, because there is a warning about mercury in fish in Maine’s fishing rule book. Bob Sinclair presented questions about mercury in the environment, then went around the room giving the students chances to answer. One young man drew a chart showing how the mercury goes from coal-fired electricity generating plants in the Midwest to Maine and into our fish.

Another told us which fish species were of most concern, and which “piscivorous” mammals are at risk. I appreciated it when Bob used “fish-eating” instead of that word I’d never heard before. And when the students reported that bass are of particular concern, my ears perked up. I thought the primary problem was in brook trout.

Well, to put it mildly, while I was there to teach the students, they ended up teaching me. As we closed out the two-hour class, I told them that, as individuals, and acting together, they will determine the sustainability of bats, brook trout — even the planet. I urged them to act wisely and with knowledge. And to be careful.

George Smith is a writer and TV talk show host. He can be reached at 34 Blake Hill Road, Mount Vernon 04352, or georgesmithmaine@gmail.com. Read more of Smith’s writings at www.georgesmithmaine.com.