Just the other day, I killed a fish. Not because it was going to be anybody's dinner or because it was an inevitable consequence of something else I needed or wanted. In fact, keeping it for dinner would have violated the permit I was operating under. I killed it because it was a human mistake that led to the fish existing in the first place. I killed it as one small act in an larger effort to keep the Bonneville Cutthroat Trout from going extinct.
It's an uncomfortable act killing just because it is scientifically desirable. People who go into environmental careers do it because at some level, they love wildlife and the outdoors. They want to see nature abound with life. If we considered the fish as an individual with rights, killing an animal to save another just seems by itself like a hollow moral calculus, because western societies have generally decided that the rights of individuals are more fundamental than the rights of the culture you belong to. However, in the pursuit of the preservation of species diversity, scientists value the species over the individual. Killing for conservation is actually quite common. In New Zealand entire islands have all their rats exterminated to allow the reintroduction of native birds and reptiles. In Alaska entire islands have all of their non native foxes exterminated to preserve birds. In South America, entire islands have all of their goats exterminated to halt erosion and favor native plants. If the United States could find a way, it would exterminate all the Brown Tree Snakes in Guam, even if it meant parachuting in poisoned mice by the thousands.
Knowing all about it doesn't make it feel any more cozy. I had been excited, it was my first day catching three fish in the trap at the top of the fish ladder instead of just one or even none. I had been taking pictures to show my kids all the fun fish I was working with. The first one I pulled out of my bucket had a reddish stripe on its midline. It was a rainbow-cuthroat hybrid, descended from the short sighted government policy of stocking fertile rainbow trout in areas where they weren't native. Generations and generations of forcing fertile contact between two species which don't interbreed in nature often forces one of them to extinction, its genetic identity swamped out of existence. So, I told the fish that despite the heroic journey swimming upstream to the top of my fish ladder, its journey was at an end. I walked with it to the opening of the fish ladder, squeezed it to death, smashed its head against a metal railing in case it was only stunned, and threw it back in the river. Watching the silvery arc it made against the sky, I wished I didn't have to. It was a mistake the fish ever existed in the first place.
6 months ago