Are we winning or losing the ongoing battle for salmon habitat?

It has been said that the Puget Sound ecosystem would be far worse off today were it not for the millions of dollars spent on restoration projects over the past 25 years.

Undoubtedly, that’s true, but I think most of us are hoping that these costly efforts will eventually restore salmon populations while improving conditions for other creatures as well. Shouldn’t we be able to measure the progress?

Juvenile chinook salmon
Photo: John McMillan, NOAA

This basic question became the essence of my latest story published in the Encyclopedia of Puget Sound: “Are we making progress on salmon revovery?”

As I describe in the story, what seems like a simple question becomes tangled in the difficulties of measuring population and ecological changes. It turns out that you can’t just count the fish to see if restoration is working. That’s because natural variabilities of weather, ocean conditions and predator/prey populations cause salmon populations to swing wildly from year to year no matter what you do.

While researching this story, I learned a good deal about freshwater habitat conditions needed to help various species of salmon to thrive. Habitat improvements resulting from restoration projects are no doubt helping salmon in significant ways. On the other hand, one cannot ignore human development that continues to degrade habitat — despite improved regulations designed to reduce the damage.

I’ve heard some people say that wild salmon would come back in larger numbers if everyone would just stop fishing for them. This may be true to some extent, especially for high-quality streams that may not be getting enough salmon to spawn. But the key to the problem is understanding the “bottlenecks” that limit salmon survival through their entire lives.

A stream may have plenty of adult spawners, but that does not mean the salmon runs will increase if the eggs are buried in silt or if food supplies limit the number of fry that survive. There may be multiple limiting factors that need to be addressed to ensure healthy ongoing salmon populations.

Small improvements in habitat may actually boost the productivity of salmon in a stream, meaning that more salmon will survive. But the benefits of small projects on large streams may be difficult to distinguish from natural variation. Statistical analysis is used to determine whether increases or decreases in salmon populations are more related to habitat changes or natural variation. It takes a fairly dramatic change to link cause to effect in a statistically significant way.

One ongoing experiment is measuring changes in fry populations in several streams within the same watersheds. One stream is left alone — the “control” stream — while habitat improvements are made in others. Because the streams are closely related, biologists hope to attribute population increases to habitat improvements with a high level of certainty. See Intensively Monitored Watersheds on the website of the Washington Department of Fish and Wildlife.

The same issue of statistics applies to the aquatic insects that salmon eat. It appears that food supplies are improving in many salmon streams as a result of restoration, but not all benthic invertebrates are responding in the same way. For many streams, it will take more time to get enough data to determine whether the increased bug populations are statistically significant. This happens to be one issue that I side-stepped in the latest story, but I will be returning to it in the future. For background, check out an earlier story I wrote for the Encyclopedia of Puget Sound, “Healthy Streams, Healthy Bugs.”

While habitat restoration is ongoing, so too is human development, which continues unabated at what appears to be an accelerating pace. New regulations are designed to result in “no net loss” of important habitats, including shorelines, streams and wetlands. But questions remain about whether local regulations themselves and/or enforcement of the regulations are adequate.

Biologists at NOAA’s Northwest Fisheries Science Center are conducting research to determine whether habitat changes are for better or worse, especially with regard to chinook. We should see some results within the next few years, as the agency prepares to draft the next five-year status report for Puget Sound’s threatened chinook population.

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