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Hatcheries Fail to Breed Fish with Instincts

by Sophia Yin
San Francisco Chronicle, July 17, 2004

Coho salmon populations decline despite human efforts

I enjoy being human. It comes with many advantages, such as having a big brain.

But lately it becomes clearer to me that in order to reap the advantages of this somewhat excessive mass of gray matter, you have to actually use it. The more I look, the more I see us humans walking around with our big brains making enormous manipulations to our surroundings before we've exercised our cerebral neural circuitry and considered the consequences.

Take, for instance, the situation we've created with the Coho salmon. Salmon are hatched in creeks and rivers, where they live for one to two years before they go out to the ocean. Once in the ocean, they hunker down for six months to five years before they fight their way back to their natal creek to spawn, and then, somewhat romantically, die, hopefully leaving future generations to carry on their genes.

So what's the problem? Anyone who knows about fish knows that salmon are in rapid decline in California. You might think it's simply because of overfishing, but the problem runs deeper that that.

Jason Watters, a behavioral ecologist at UC Davis, points out that the state has a long history of manipulating land and water. "We put dams on major rivers, create diversions for agricultural and urban water use." It's not hard to figure this one out. "You take the water away from the fish and the fish have a hard time getting by," he said.

But as these changes were being made, we and our big brains figured that we could easily counter the negative effects by raising salmon in hatcheries in order to gain numbers to bolster the populations.

So for the past 100 years we've been doing just that, but despite introduction of huge numbers of hatchery fish, the salmon population continues to decline. "Annually, more hatchery fish are released into California rivers than were probably ever naturally produced, yet populations continue to decline," Watters said. For instance, in the Sacramento River the salmon populations have dwindled from a healthy 200,000 in the 1950s to less than 50, 000 today.

A cursory glance and this decline is a puzzle. After all, common sense says that if you produce more salmon or widgets or anything else for that matter, you should have more. But we're not dealing simply with scaly widgets that live in the water. We're dealing with animals that live in a complex environment. They need more than good health to survive and reproduce, they need street smarts, too, which is what hatchery salmon lack.

"Domestic hatchery salmon don't behave right," Watters said. They orient themselves toward the surface as juveniles instead of hiding safely at the bottom of the stream, they're oblivious to predators such as birds and large mammals overhead, they're always aggressive rather than being aggressive primarily when holding onto a territory like their wild counterparts, and they don't imprint on their home streams that well, so they often go astray.

One look through the eyes of a behavioral ecologist at how these fish are raised, and it's crystal clear. Unlike a creek with its complex flows and corresponding variance in food availability, hatchery creeks are straight pools of water housing 10,000 to 20,000 salmon in a space where you might find 200 to 300 salmon in the wild.

There's no learning to forage for food or to avoid overhead predators here. In fact, if you wanted to tame fish so that that they'd come up to you and be your friend, you'd do exactly what the hatcheries do, send a large mammal (human) walking by at least once a day to toss food in. These sardine- packed fish also lack the environment for developing good social behavior, which is one reason why they're always aggressive, and it also explains why most don't really know how to mate.

Because of their large numbers, high level of aggression and desire to mate, they can hinder wild salmon from mating. And even when they do mate, it can be a problem. Hatcheries over many generations have selected salmon best adapted to living in hatcheries and not as good at living in the wild. Thus interbreeding could be rapidly tainting the genetic pool and destroying diversity, the downfall of many now-extinct species. The homogenous hatchery creates a homogenous population where a diverse population is most likely to survive.

What's the solution? Right now, it's converting hatcheries to mitigation or conservation hatcheries to try to produce salmon that are both more genetically similar to wild salmon so they can interact and breed with wild ones. This requires fewer fish raised in a more diverse environment, and if these practices aren't perfected soon, we and our big brains will no longer know the sight of salmon in California.

Sophia Yin, DVM, is a small-animal veterinarian in Davis with an animal-behavior Web site at
Hatcheries Fail to Breed Fish with Instincts
San Francisco Chronicle, July 17, 2004

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