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Deep Crisis:
Frontiers' Scientist Answer Your Questions

by Dr. Michael Schiewe
PBS Frontiers, April 2003

Scott Levy asks:
What would you estimate are the odds that we will follow the 2000 Biological Opinion?

Is it possible to triple survival in some life stage of Idaho salmon/steelhead without the removal of the 4 Lower Snake River dams? If yes, please describe what efforts would provide these results.

Schiewe's response:
The first question refers to the Biological Opinion written in the year 2000 by the National Marine Fisheries Service. This Opinion covers operation of the 29 dams of the Federal Columbia River Power System between the years 2000 and 2010. The Biological Opinion describes what are referred to as "reasonable and prudent alternatives" or RPAs that when implemented by the "actions agencies" are designed to avoid jeopardizing the continued existence of the listed salmon. This is a regulatory document; and the short answer to your question is that, "I don't know." I suggest you contact the federal agencies that are governed by the Biological Opinion and ask them this question. The action agencies for this Opinion are the US Army Corps of Engineers, the Bureau of Reclamation, and the Bonneville Power Administration.

The second question involves the role of the four lower Snake River dams in the decline and continued depression of Snake River salmon, and the potential role their removal might play in recovery. This has been a very contentious issue in the Pacific Northwest during the past decade, and is one that has generated substantial coverage in the popular press. While it is relatively clear to everyone involved that removing the dams would be good for fish, the exact role that continued operation of dams is playing in the continued depression of the salmon populations passing them is the subject of much debate.

The manner in which you ask the question suggests that you think that removing the four lower Snake River dams would triple the survival of some life stage of Idaho salmon and steelhead. I'm unaware of any credible scientific study or analysis that would support this conclusion, and would be interested in learning of it if it exists.

In contrast, in a paper recently published Dr. Peter Kareiva and colleagues (Kareiva, P., M. Marvier, and M. McClure. 2000. Recovery and management options for spring/summer chinook salmon in the Columbia River basin. Science 290:977-979) it suggests otherwise…that removing the 4 Snake River dams would be unlikely to by itself effect recovery Snake River salmon. Using 1980 to 1993 returns of spring chinook salmon populations originating in the Salmon River (a tributary of the Snake)as a baseline, Kareiva et al. found that none of the populations were surviving at a rate high enough to replace themselves…that is, each successive generation was becoming less abundant. Using an age-structured matrix model (a common tool in population dynamics modeling), Kareiva et al. showed that even improving upstream and downstream passage survival to 100% (a level unlikely even on an undamned river) the overall life cycle survival of these chinook populations would still not improve enough to achieve replacement. Further, these investigators concluded that the only conceivable way that removal of the Snake River dams could effect such a large improvement in survival would be if their removal eliminated a very high level of mortality that was occurring as a result of their presence, but at some later life stage. Such a "deferred mortality" has been proposed by some, but has yet to be demonstrated.

The bottom line is that the dams are one of many factors that contributed to the decline of Snake River salmon. I'm not aware of any "silver bullet" that might triple survival of any particular life stage. Recovery of salmon in the Columbia River will no doubt require improvements in survival throughout the life cycle, and logically involve careful management of hatcheries, continued efforts to improve passage survival, carefully controlled harvest, and landscape-scale habitat restoration…and last but not least, a return of nearshore oceanic conditions that support much higher marine survival. While the latter is obviously beyond the control of humans, the current evidence does in fact suggest we are entering a period of more favorable marine conditions, and that the salmon are responding with near record returns.

Dawn Gilkison asks:
Alan Alda's narration states that "a higher proportion of barged fish return as adults, compared to those that came down the river on their own." Could you give me a reference from the scientific literature containing data that supports this statement?

Schiewe's response:
Since the 1970s there has been a series of evaluations comparing the survival and return of transported versus non transported fish. The majority of these studies have indicated a higher returning proportion of transported when compared to non transported fish. However, the results varying by species of salmon and the years over which the evaluations were conducted. In some of the more recent years in which passive integrated transponder (PIT) tags were used for these studies, fishery scientists have been able to evaluate the effects of transportation in much greater detail…to include on a week-by-week basis throughout the migration season. In some of these studies it has been found that there are periods during which the non transported fish survive and return at a higher rate than do the transported ones.

Citations for some of the recent research reports that include adult return data for the 1995, 1996, 1998, and 1999 migration years are as follows:

Citations from the scientific literature that report results of juvenile salmon transportation studies include the following:
Dr. Michael Schiewe is a Fishery Biologist specializing in the ecology of Pacific salmon. He received his undergraduate education from Humboldt State University in northern California in 1968, and his Masters and PhD degrees from the University of Washington in Seattle, in 1976 and 1980, respectively. Dr. Schiewe's early research focused on variety of fish health issues, ranging from infectious diseases of fish and shellfish, to the effects of environmental contaminants on marine and anadromous fish. For the past 12 years, he was Director of the Fish Ecology Division and Senior Salmon Scientist at NOAA Fisheries' Northwest Fisheries Science Center. In this capacity, he directed a variety of research, including studies on biodiversity and population structure, fish passage at dams, habitat requirements, artificial production, and estuarine and ocean ecology of Pacific salmon. Dr. Schiewe is currently a Senior Fishery Scientist at Anchor Environmental LLC in Seattle, Washington.
Deep Crisis: Frontiers' Scientist Your Answer Questions
PBS Frontiers, April 2003

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