Questions and Answers About the Extinction Clock Study

Thu, 07/08/1999

Questions and Answers About the Extinction Clock Study

Questions and Answers About the Extinction Clock Study


7/9/1999 --  --  Why did Trout Unlimited sponsor this study?

One of the recurring messages circulating in the region is that "more study is needed" before the big decisions on salmon restoration, such as the proposed partial removal of Snake River dams, can be made. We decided the ask the rather obvious question, "How much time do we really have?"

How can the study pinpoint a date of extinction?

The study is based on a very simple principle. Each year salmon return to Snake River tributaries to spawn. Since salmon die after spawning, each spawner’s mission is to produce enough offspring to provide at least one spawner for the next generation. When the next generation of spawners returns an average of 5 years later to the same place, we compare their numbers to those of their parents. If spawners in the next generation number fewer than their parents, (a spawner to spawner ratio of less than 1.0) the population is declining. By measuring how fast the population is shrinking, we can estimate the year in which the population will reach the extinction threshold.

Obviously, we can’t predict the exact day and time that wild spring chinook salmon in the Snake River will become extinct. We can, however, say in what year the salmon’s population is most likely to drop below the extinction threshold. Dr. Mundy has developed a scientifically sound method of estimating when salmon would go extinct if current conditions continue. The method was applied to spawning ground counts for 16 years at 13 of the best spawning sites in the Snake River basin. The study projected 2017 as the year in which the strongest of the five living generations of Snake River spring chinook, the 1988 brood line, is most likely to reach the point of functional extinction. The other four generations have smaller numbers of spawners, so they are expected to be functionally extinct before 2017. Changing conditions could mean that the actual date of extinction could come somewhat later – or earlier. However, we are certain that the process of extinction has already begun in some spawning localities, and that 2017 is the year in which functional extinction is most likely to occur, based on current conditions and rates of decline over the last two decades.

Is it scientifically valid to forecast the future in this manner?

The future is always uncertain, but our experience with Snake River spring and summer chinook tells us that spawners in 11 of the 16 years studied did not replace themselves. Spawners have not replaced themselves in the last six years of our study. If the current rates of return remain the same or get worse, the reproductive activity of the fish will cease and the spawning population will become extinct. The method for developing the linear trend analysis that established the time line uses accepted scientific methodology and has been peer reviewed. Perhaps most important, this study is validated by what is happening in the "real world," on the spawning beds in the tributaries. Real world experience makes it clear that localized extinctions have already occurred in some of the Snake River tributaries.

Why did Dr. Mundy use spawning ground counts for this study?

Spawning ground counts are the most reliable data available on the future of the population. The number of spawners puts an absolute limit on the number of salmon that can be produced in the future. The numbers of spawners are based on fish counted by biologists working in the best remaining spawning habitats of the Snake River basin. Dr. Mundy believes that the spawning ground counts give the most accurate picture of the state of wild fish because they measure the only important gauge of population health: whether enough fish are returning to the spawning grounds to maintain the population.

Why is this more accurate than other methods?

Dr. Mundy believes spawner to spawner ratios are the best indicators of the future of the populations because they are the least likely of all methods to overestimate the number of fish that spawn in the wild. Counts at dams always overestimate the size of the wild spawning populations because they include hatchery fish and stray wild fish. Even if hatchery fish and strays could be accounted for, dam counts would still overestimate wild spawners, because some fish die in the weeks and months between dam passage and spawning. Only fish that are alive at the time of spawning have a chance to contribute to the future of the populations, and spawning ground counts are the best measure of live fish on the spawning grounds.

What is causing Snake River Spring Chinook to decline?

The cause for decline is that human activities keep the number of salmon too low to cope with variability in natural factors such as annual snow pack. The National Marine Fisheries Service identified a large number of human activities and natural events as factors that contribute to the decline. The human factors are lumped together as the four H’s: hydroelectric dams, habitat loss, hatchery misuse, and harvesting too many fish. Unfavorable ocean conditions are often cited as a major natural factor in decline, but salmon dealt successfully with all kinds of ocean conditions for thousands of generations before they were forced to cope with the four H’s.

What will it take to restore these populations?

Human factors that cause mortality, the four H’s, have to be controlled to the extent necessary to permit salmon to once again successfully cope with the full range of natural factors, including ocean conditions. Success means that spawner to spawner ratios would be greater than replacement level (1.0) on all spawning grounds in each generation. Experience teaches us that the salmon have the capacity to produce at rates 10 to 20 times the rate of replacement, if given the chance.

If the study states that some fish will still be coming back after the projected date of extinction, why does it say they will be extinct?

Extinction is not an "all or none" one-time event, but it is a continuous process that may at times be reversible. Extinction from the wild can occur well before the last animal has died, or before the last isolated population has been extinguished. In the early stages of extinction for salmon, populations that could support one another by exchanging spawners are isolated. Once a population has been cut off from the possibility of receiving spawners from other, possibly stronger populations, it is far more vulnerable to extinction than it would otherwise be. Toward the end of the process of extinction, low numbers of spawners heighten the risk that eggs will go unfertilized, or that no eggs will be available to fertilize. For the purposes of this study, effective extinction for a population was set at 15 spawners per year or less. Scientists consider this a conservative number. At numbers below that, the loss of genetic diversity and a loss of fitness to adapt to changing environmental conditions becomes a virtual certainty. When this occurs, we can safely say that the population is functionally extinct.

The study applies to wild fish. What about hatchery fish?

As the Endangered Species Act has been applied to salmon, most hatchery fish do not count as part of the protected population. The definition of salmon recovery is that there are stable populations spawning in the wild. More importantly, from a scientific perspective, hatchery fish may have a diminished ability to successfully spawn in the wild. The loss of genetic diversity, which allows salmon to adapt to changing environmental conditions, is always a concern with hatchery fish, as are outbreaks of diseases resulting from confinement in crowded conditions.

This study only applies to spring chinook. What about Snake River fall chinook and steelhead?

We chose spring chinook because of the availability of spawning ground counts for those fish over a long period. Spring chinook spawn in the clear water of tributaries and are easier to count than the fall chinook, which are harder to count because they spawn in the mainstem of larger rivers. A similar study could be done for steelhead. We suspect that similar studies would produce similar results.

Some have blamed the decline of the salmon on poor ocean conditions. If ocean conditions improve, will this affect the projections in the study?

If ocean conditions improve and the human factors of decline – the so called four H’s – do not get worse, it will prolong the process of extinction. Conversely, a string of years of poor ocean conditions would shorten the time frame to extinction. It is important to note that the study period looks at spawning ground counts over a 15-year period, which includes a range of ocean conditions, including good years and "normal" years. Dr. Mundy believes that a short span of four "good years" in the 1980’s, possibly related to the weather that produces exceptionally good ocean conditions for salmon, is the only reason that there are now any spring and summer chinook spawning in the wild in the Snake River basin. Unfortunately, even a run of four or five exceptional years would not have the same effect now as it did in the 80’s, because there are now fewer spawners. In most years ocean conditions are average to poor, and in average to poor years, spring and summer chinook spawners are not replacing themselves. Exceptional ocean conditions can only serve to prolong the process of extinction in the absence of improvements in the four H’s.

This study is alarming. Do we have enough time to prevent extinction from happening?

It is very alarming, but there is still time to prevent the extinction of wild spring and summer chinook from the Snake River basin. The good news is that these fish have tremendous reproductive capability given the right conditions. However, the study is a clarion call that actions to restore salmon must be taken very quickly.

Why hasn’t the National Marine Fisheries Service conducted a similar study?

Good question. NMFS did fund similar studies, called the PATH analysis, that were based on somewhat different data (recruit to spawner ratios) and more optimistic assumptions. NMFS recruit to spawner ratios differ from our spawner to spawner ratios in that "recruits" include numbers of fish that could have spawned, not those that actually did. NMFS studies assumed, as we did not, that conditions for salmon survival would improve in the future. Even so, their conclusions differ from ours only in assessing the degree of risk of extinction, not in the fact of the risk of extinction. In the Draft Anadromous Fish Appendix to the Draft Environmental Impact Statement regarding the four lower Snake River dams recently published by the National Marine Fisheries Service, they acknowledge that there is a risk of extinction in delaying actions to address the decline but state that they have no way of assessing the degree of risk.

Press Release
Questions and Answers
Background and Summary
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Download the full report in .pdf format
Take Action Now to Save the Salmon: Write Congress
Take Action Now to Save the Salmon: Write Vice President Cheney

Date: 7/9/1999


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