To Kill, or Not to Kill

One camp argued that we had no business playing God and deciding which fished lived, and which died. I was in the other camp

By Rob Breeding

Biologists routinely make decisions regarding the fate of the animals they study. I got a taste of this in the Bitterroot/Selway Wilderness 20 years ago while on a summer job with the Forest Service doing fisheries work.

While snorkeling to count fish, we’d stumbled upon what seemed to be a swarm of juvenile rainbow trout.

We dutifully recorded the rainbows in our log books, but the whole thing didn’t sit right with our crew leader, Mike. For weeks he brooded over those fish. We hadn’t found rainbow fry elsewhere in the headwater streams during our sample work; just that swarm on the main river. And while rainbow like, the fry seemed different. We hadn’t noticed parr marks and the fish had a forked tails.

Mike was convinced the fish were actually chinook salmon and was determined to capture one so we could verify its species back in the lab. Near the end of our summer assignment, he fashioned a net out of a plastic bag and a forked pine branch, put on his dry suit and spent an hour in the Little Clearwater River trying to net one of the baby fish.

Eventually he did.

Mike was grinning as he came back to camp, salmonid fry swimming in the plastic baggy like a goldfish he’d just won at the fair. That’s when a fierce debate about the ethics of killing fish broke out. I’ve never participated in a more passionate argument that didn’t involve me taking out the trash.

One camp argued that we had no business playing God and deciding which fished lived, and which died. Besides, the fish we killed might have been the only one of the brood to run the gauntlet and make it back from the Pacific to spawn. Finally, this camp argued, the protocols for our assignment mandated counting, not collecting, fish.

I was in the other camp, arguing that the value of verifying a scientifically important remnant run of native salmon outweighed the cost of killing one fish. But Mike was swayed by the other guys, and released his catch.

When we got back to Hamilton and related the story to our project supervisor, he laughed. Hearing our description he agreed it was probably a chinook, but explained that there had been decades of salmon introductions into the watershed and it was highly unlikely the fry was of wild origin.

I watched similar debates unfold on the other side of the divide as crews sampled for invasive brook trout in the Bitterroot River headwaters. Brookies are bad news in bull trout habitat. They can out compete the native fish, as well as spawn with them. Fortunately, the hybrids from such blasphemy are infertile, but you still lose a year class of bull trout.

When crews found brook trout where they weren’t supposed to be they faced the question: Toss the invader in the knapweed or put it back in the creek?

As the focus on native fish grows, biologists are increasingly facing dilemmas such as this. Chris Clancy, a long-time FWP biologist in the Bitterroot, said recently that he doesn’t have a problem killing invasive trout, when that’s the point of a project. But tossing the incidental fish on the bank isn’t going to stop an invasive species. Where there’s one there are certainly many more.

In the case of rainbow/cutthroat hybridization, Clancy said determining which fish is which can be tough, even for pros. In a test, photos of 60 rainbow/cutthroat hybrids were sent to fisheries biologists, and there was significant variation in what some called cutthroats, and others didn’t. The only way to know for sure is genetic testing.

I doubt cable channel AMC has a “Swimming Dead” program in development. Regardless, the zombie swarms of cutthroat/rainbow hybrid trout are different from fictional zombies in an important way: they are sexually fertile. That’s what makes them especially difficult for fisheries managers.

Pure strain fish will segregate during spawning. But once a male cutthroat succumbs to the temptations of a sexy rainbow and makes a bunch of hybrid babies, telling the good fish from the bad becomes next to impossible, unless you get a DNA sample back to the lab.

This is the second in an ongoing series on native fish

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