Review of Salmon and Steelhead Supplementation

Read the report in 3 parts:

Related links:


The report was completed in response to NOAA Fisheries and Northwest Power Planning Council requests for the ISAB to consider the benefits and risks of supplementation to natural populations of salmon and steelhead, and whether natural and artificial production could be integrated to increase the capacity and productivity of the combined population for the foreseeable future.

The ISAB reviewed the genetic risks, and models of the demographic benefits, of supplementation, performance indicators to evaluate supplementation, decision-making tools for supplementation risk-benefit assessment, and surveyed the status of Columbia River Basin supplementation projects.

The ISAB's primary conclusions are:

  • While supplementation is ongoing, it can often be expected to increase the number of salmon and steelhead spawning naturally in the target population, and this may provide additional harvest opportunities, compared to the situation with no artificial production.
  • The increased population size and productivity attributable to supplementation will likely not persist once supplementation ceases.
  • Supplementation can reduce the natural spawning fitness component in the integrated population and this reduction in natural spawning fitness will persist in the natural spawning population for some number of generations after the termination of supplementation.
  • Data to calculate the correct performance indicators are not being collected regularly in supplementation projects. Because of the widespread lack of reference populations, neither benefits to abundance, nor risks to natural spawning fitness, can be effectively quantified at present.
  • Except for critical cases where a natural spawning population is literally on the verge of extinction with no credible options for rescue by habitat improvements or harvest management, a technically valid risk-benefit assessment of supplementation to decide upon whether supplementation should be undertaken in any particular stream will be dominated by uncertainty because the data needed for the assessments are largely unavailable.

The ISAB recommends:

  • Use supplementation sparingly, and only implement in a subset of the locations where unharvested natural populations are not replacing themselves, where habitat capacity is believed to be able to accommodate additional production, and where landscape conditions and institutional considerations are suited to maintaining the integrity of the experimental design.
  • Where supplementation is used, it should follow a protocol that uses natural-origin adults from the target population as parents in hatchery spawning.
  • Establish and monitor performance standards for each project for natural-origin and hatchery-origin adult abundance and per capita production rates.
  • Conduct all supplementation projects with explicit experimental designs to reduce uncertainty and contain supplementation risks. Establish reference populations, adequate monitoring, and objective means to assess when supplementation should be terminated (due to either success or failure).
  • Coordinate the multiple supplementation projects across the Columbia River Basin so that in aggregate they constitute a basinwide adaptive management experiment. The Fish and Wildlife Program should include mechanisms to ensure that individual projects are collecting the data necessary to test their effectiveness and ensure regional coordination of the multiple experiments.

Implementing these more rigorous experimental protocols should improve the scientific understanding of whether supplementation can contribute to salmon and steelhead recovery at a tolerable cost to natural spawning fitness of wild populations.

September 24, 2003 follow-up report (see also in PDF format)

To: Judi Danielson, Chair, Northwest Power and Conservation Council
Olney Patt, Jr., Executive Director, Columbia River Inter-Tribal Fish Commission
Usha Varanasi, Director, NOAA-Fisheries Northwest Fisheries Science Center
D. Robert Lohn, Regional Administrator, NOAA Fisheries

From: Eric J. Loudenslager, Chair, Independent Scientific Advisory Board

The ISAB thanks the Northwest Power and Conservation Council for the opportunity to report on the findings and conclusions of our supplementation report at the Council's June 2003 meeting in Boise. We also thank the Northwest Fisheries Science Center and the Columbia River Inter-Tribal Fish Commission for their review comments.

Supplementation is a complicated topic. There is an ongoing debate among managers and scientists as to whether this strategy increases the abundance of natural origin adults and what effect it has on the natural spawning replacement rates-both quantities are critical to the recovery of self-sustaining salmon and steelhead populations. For these reasons the ISAB supplementation report was lengthy and detailed.

Council members had many questions for the ISAB during our presentation. Based on these questions, the ISAB concluded that a brief summary of our conclusions and recommendations could assist the Council, NOAA Fisheries, and CRITFC in identifying the priority issues in our report. That summary follows. If Council, NOAA Fisheries, or CRITFC executives or staff scientists request, the ISAB would be pleased to provide further elaboration of the summary points.

Hatchery fish are not the same as wild fish. Fish adapt genetically (evolve) to the conditions of hatchery rearing, a process termed domestication. They also will evolve new life history strategies as they adapt to completing their life cycle in the wild after their release from the hatchery. When compared against wild stocks, production hatchery stocks usually have lower adult-to-adult reproductive success when breeding in the wild. Because many of the traits associated with domestication are determined genetically, allowing domesticated salmon to interbreed with wild salmon will reduce the fitness of the integrated (mixed hatchery/wild) population spawning in the wild.

The degree of domestication for any given population depends on the number of generations that the population has spent in hatchery breeding and the strength of domestication selection. In a hatchery population maintained by deliberately isolated (closed) breeding, the level of domestication is generally high. For this reason it is to be expected that a supplementation program that simply allows large numbers of individuals from a closed hatchery line to interbreed with a self-sustaining wild stock of the same species will have considerable negative effects on the natural spawning productivity and viability of that wild stock. This conclusion formed the basis for the ISAB recommendations in the hatchery surplus report (ISAB 2001-3).

Some supplementation programs propose to maintain their lines by an integrated breeding protocol that uses some wild-spawned fish for broodstock in each generation and that limits the numbers of hatchery-spawned fish that are allowed to breed in the wild in each generation. Such a protocol results in a pedigree in which some of the recent ancestry is from hatchery breeding and some is from natural breeding. These types of protocols will cause less domestication than long-term exclusive (closed) hatchery breeding, but they do not eliminate domestication. For that reason these programs still pose a risk to the viability of wild stocks.

There has not yet been enough experience with supplementation programs that are based on defined integrated breeding protocols to quantify how much domestication will occur in such programs or how much damage they will cause to the natural spawning life cycle performance of wild stocks, as measured by adult-to-adult replacement rates of the wild spawning fish. It also is not yet clear how effective such programs will be at increasing the number of naturally spawning fish of naturally spawned origin, if they comply with the defined broodstock and outplanting constraints.

It is for these reasons that the ISAB and ISRP have recommended that supplementation of an existing wild stock should be implemented only on an experimental basis, in settings where some probability of damage to the wild stock can be tolerated, and where the progress of the experiment can be monitored. Effective monitoring is critical to ensure that we will learn from the experiment how much domestication really occurs, what is the effectiveness of such a program for increasing recruitment from natural spawning, and what is the cost to natural spawning fitness. To be effective for this purpose, monitoring in each such experiment must measure, over time: 1) the actual rates of drawing naturally spawned and hatchery spawned fish for broodstock, 2) the actual proportions of naturally spawned and hatchery spawned fish on the spawning grounds, 3) the natural spawning replacement rates in the supplemented population and in an unsupplemented control, and 4) the number of naturally spawning fish of naturally spawned origin in the supplemented population and an unsupplemented control. Because of natural variation in salmon productivity from one year to the next, and imperfect matching of treatment and control stocks and environments, reliable conclusions will require results from a number of implementations of this design. At present the experimental design(s) of the supplementation projects in the Columbia River Basin, based on the projects reviewed in our report, will not resolve these uncertainties.

These concerns about scale, experimental design, experimental control, and monitoring needs have been at the heart of the issues raised by the ISRP in their reviews of specific supplementation programs. These same concerns were explained in detail in the ISAB general review of supplementation.

Public enthusiasm over the record returns of salmon of the last few years further challenges us as scientists and managers to adequately communicate why these large current returns of mostly hatchery fish are not a sufficient measure of success at restoring wild populations. The critical evidence will be determining whether natural spawning by these returning adults is more or less productive than unsupplemented wild stocks, under equivalent conditions. We must bear in mind that even though present ocean conditions are good, they are expected to continue to cycle. As a result, it is important to determine not whether hatchery-based production has supplemented the natural returns in these recent years (it generally has), but whether these natural spawners (hatchery and wild) produce increased numbers of adult progeny in future years.

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