Fishy Chinook Salmon Data
5 Apr 2006 in Regulatory Science, Information Quality
A recent news report highlights why high quality information is essential for the public to understand ecosystem issues, and for government officials to make informed decisions.
On April 2 the San Francisco Chronicle published a Page One story by environment writer Glen Martin concerning Klamath River Chinook salmon. The Klamath River runs from southern Oregon through the Coastal Range to the Pacific Ocean south of Crescent City. Useful maps of the Klamath Basin can be found here. An 11-mile segment has been designated "wild and scenic," and is protected from virtually all competing uses. Some segments have Class IV+ or Class V rapids.
The general issue presented in the Chronicle concerns competing upstream uses of Klamath River water. In general, the more water that is removed for agricultural use upstream the less water remains to sustain fish populations. Salmon present a special concern. They are anadromous, which means they live in the sea but migrate to fresh water to breed. They also are programmed to return to the same river segment where they were spawned.
The specific issue concerns the 2006 salmon harvest. Martin reports that the federal government is poised to cancel or severely curtail this year's fishing season "because of collapsing stocks on the Klamath River."
Though the situation is mired in competing scientific theories, lawsuits and political skirmishing, the bottom line is fairly simple: There are plenty of Chinook salmon in the ocean now, but most of them originated in the Sacramento River. Salmon from the Klamath River, once a producer of millions of fish, are at all-time lows, compelling federal protections. Fewer than 30,000 Klamath Chinook salmon are expected to return to the river this year, well below the 35,000 fish biologists say are needed to sustain the runs.
And because both populations mingle in the open sea, fishing for Sacramento River Chinook could imperil the Klamath salmon that remain.
It's certain that biologists who study California salmon and the Klamath River and the federal officials who must make decisions know much more than what Martin has summarized. Nevertheless, there are important information quality questions that citizens (and federal decision-makers!) ought to ask. For example:
- How precise are these figures? Precision is different from accuracy. Measuring meters with a laser calibrated in yards will get you very precise measurements--but of the wrong thing. A common way to describe precision is with significant figures. Values that are precise can be highly inaccurate if the tool used to measure or estimate them is systematically flawed in some way.
- Are these figures accurate? Accuracy generally refers to how well a measured or estimated quantity conforms to the actual thing being measured or estimated. A measure or estimate is accurate if it conforms with a specified amount of error to the thing being measured or estimated Statisticians refer to this type of accuracy as unbiasedness, and it's fully appropriate for statistical information such as the number of salmon expected to return to the Klamath River to spawn or the number of adult salmon needed to sustain the population. Values that are accurate can be highly imprecise if the tool used to measure or estimate them is not carefully calibrated.
- Are these figures objective? Under federal information quality standards, accuracy is similar to (but not quite identical with) "objectivity." A measure or estimate is objective if it is as likely to underestimate as to overestimate the true (but unknown) value. Objective estimates must be "accurate" in the sense that they are unbiased, but they need be "precise" only within the amount of precision specified.
So how should we interpret the Chronicle story? It depends on the accuracy, precision and objectivity of the reported estimates, and unfortunately, Martin offers little insight into these factors. Depending on how they sort out, 30,000 returning salmon could be vastly below the 35,000 needed to sustain the Klamath River population. Or the figures could overlap by a lot. Or they could be indistinguishable from each other. We just don't know.
One reason to be wary is that Martin reports the estimated number of salmon expected to return to the Klamath River as "fewer than 30,000" (our emphasis), but leaves out any hint about how many fewer than 30,000 he has in mind. That compounds imprecision with ambiguity.
Posted 5 April 2006.
Corrected 12 April 2006.