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The Steelhead Family Tree

Posted by | September 27, 2008

From judges deliberating in federal courthouses to fishermen wading into streams, many people have ideas about how to restore salmon and steelhead runs in the Northwest.

When Gary Thorgaard, director of Washington State University’s School of Biological Sciences, thinks about salmon and steelhead recovery plans, his framework of analysis includes the genetics that link the fish to one another through hundreds and even thousands of years of their family trees.

From time to time, federal judges encounter Thorgaard’s area of expertise when they rule on how different wild salmon and steelhead are from those that are raised in hatcheries. That’s a key legal component to decisions about what fish should be protected under the federal Endangered Species Act.

“I think there’s a shortage of good science related to that question,” Thorgaard said.

The Endangered Species Act was passed by Congress and signed into law by President Richard Nixon in the 1970s. It’s the powerhouse law that stands behind everything from legal limits on timber sales due to spotted owl nests to allowing extra water to flow through dams to help migrating salmon and steelhead juveniles make their way downstream.

The ESA (as the law is called) depends for its full meaning on what, exactly, we mean by a “species,” that crucial element of the natural world we are trying to protect.

Here’s how the issue plays out for salmon and steelhead. The Northwest has had hatcheries in operation for about a hundred years, and over time people have created what some would call ‘domesticated’ strains of fish.

It’s a bit like the domestic dog versus the wolf. Dogs can breed with their wild cousins and have fertile offspring. That fact tends to support the idea the animals are all one species. From that point of view, a lawyer could make the argument there’s no need to protect wild wolves anywhere – because there are surely plenty of dogs around.

But, wolves and dogs have strong differences in size, shape and behavior – as well as significant differences in genetics. That supports the idea they are distinct species. The argument from this point of view is that the abundance of dogs all around us doesn’t mean we should destroy wolves everywhere.

Here’s where the details get messy. We all know of wolf-dog hybrids. Should we protect wolves in Alaska that have a little bit of domestic dog blood in them from generations ago? In short, where do you draw the line?

Thorgaard sees the differences between wild and hatchery fishes in roughly similar ways. From his point of view, there is a whole continuum or range with the purely wild salmon and steelhead on one end and those that are more purely hatchery-based on the other.

“Part of what interests me is what genes are changing along that continuum,” he said.

Here’s one difference across the range of the purely wild versus the tamer fish. The fish that have been raised in hatcheries for many generations tend to come to the surface and feed more quickly than those whose family tree is the most wild. You could say that the wild fish are more cautious about coming to the surface. Thorgaard’s students have measured exactly that caution in steelhead fingerlings in his lab at WSU.

Steelhead are an interesting and pretty flexible species. As Northwest fishermen know, rainbow trout can remain in freshwater their whole lives and successfully reproduce. But rainbows become steelhead if they migrate to the ocean. Like salmon, the steelhead return to their original streams to reproduce – at least they do so when they can.

The Ice Age history of the Northwest, with stream blockages, diversions and the overflow of lakes, has helped reshape the various populations of steelhead again and again, leading to an intricate family tree whose relations have been tracked in part by Thorgaard and his students.

“The complexity is either demoralizing or interesting, depending on how you look at it,” Thorgaard said.

Add to that complexity the differences we people are adding to the mix by raising generations of steelhead in hatcheries, and you start to appreciate the large puzzle that Thorgaard works on each day.

Thorgaard’s interests are not simply academic.

“I also fish,” he said with a smile.