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NOAA Technical Memorandum NMFS-NWFSC-41

Ecological and Behavioral Impacts
of Artificial Production Strategies
on the Abundance
of Wild Salmon Populations
A Review of Practices in the Pacific Northwest

Thomas A. Flagg, Barry A. Berejikian, John E. Colt, Walton W. Dickhoff,
Lee W. Harrell, Desmond J. Maynard, Colin E. Nash, Mark S. Strom,  Robert N. Iwamoto, and Conrad V. W. Mahnken

Northwest Fisheries Science Center
Resource Enhancement and Utilization Technologies Division
2725 Montlake Blvd. E.
Seattle, WA 98112 

March 2000

William M. Daley, Secretary

National Oceanic and Atmospheric Administration
D. James Baker, Administrator

National Marine Fisheries Service
Penelope D. Dalton, Assistant Administrator for Fisheries

NOAA-NWFSC Tech Memo-41: Ecological and Behavioral Impacts of Artificial Production Strategies on the Abundance of Wild Salmon Populations
A Review of Practices in the Pacific Northwest

NOAA Technical Memorandum NMFS Series

       The Northwest Fisheries Science Center of the National Marine Fisheries Service, NOAA, uses the NOAA Technical Memorandum NMFS series to issue informal scientific and technical publications when complete formal review and editorial processing are not appropriate or feasible due to time constraints. Documents published in this series may be referenced in the scientific and technical literature.

       The NMFS-NWFSC Technical Memorandum series of the Northwest Fisheries Science Center continues the NMFS-F/NWC series established in 1970 by the Northwest & Alaska Fisheries Science Center, which has since been split into the Northwest Fisheries Science Center and the Alaska Fisheries Science Center. The NMFS-AFSC Technical Memorandum series is now being used by the Alaska Fisheries Science Center.

        Reference throughout this document to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA.


This document should be cited as follows:

Flagg T.A., B.A. Berejikian, J.E. Colt, W.W. Dickhoff, 
L.W. Harrell, D.J. Maynard, C.E. Nash, M.S. Strom,
R.N. Iwamoto, and C.V.W. Mahnken. 2000. 
Ecological and behavioral impacts of artificial production
strategies on the abundance of wild salmon populations. 
U.S. Dept. Commer., NOAA Tech. Memo. 
NMFS-NWFSC- 41, 92 p.


Most NOAA Technical Memorandums NMFS-NWFSC are
available on-line at the Northwest Fisheries Science Center
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Production hatcheries play a major role in supplying Pacific salmon and trout to the common property fishery, and benefiting commercial, sport, tribal, and non-tribal fishers. In the Pacific Northwest hatchery fish currently contribute between 70-80% of coastal fisheries.

In the past production hatcheries have also played a role in slowing the decline of natural populations. Now, however, they are becoming increasingly implicated as one of the factors causing the decline. Among their citations include the transplantation and straying of fish, over-harvest, and effects on carrying capacity of receiving environments.

Most production hatcheries were built when wild salmon stocks were healthy, and genetic diversity of stocks was not a concern. Today, many stocks in the Pacific Northwest are listed as threatened or endangered under the terms of the U.S. Endangered Species Act (ESA), and the need to preserve biodiversity has brought about a new era of management strategies for the conservation of wild stocks. As current hatchery practices and methods are now recognized as contributors to the overall decline, there have been strong arguments for the reform of hatchery management, particularly in the Columbia River Basin. The goal is to reduce the overall impact of hatchery fish on the survival of wild stocks.

This document reviews the issues behind the major theoretical and observed ecological and behavioral impacts of salmonid hatchery production strategies on the abundance and trends of wild salmonid populations. The major focus is on potential effects of differing artificial production strategies as they relate to stocks within:

The document is divided into three principal sections, as follows:

Comparison of Hatchery and Wild Salmon Biology

Some major differences between hatchery and wild salmonids are reviewed in sections describing survival, foraging behavior, social behavior, habitat preference, response to predators, differences in morphology and physiology, and reproductive behavior. The reviews conclude that artificial culture environments condition salmonids to respond to food, habitat, conspecifics, and predators differently than fish reared in natural environments. Present culture techniques also alter selection regimes, which may result in genetic divergence between hatchery and wild populations. Finally, the phenotypic differences observed between cultured and wild fish are both genetically and environmentally controlled.

Impacts of Artificial Production Releases on Wild Fish

The impacts of hatchery reared fish on the population abundance of wild fish are reviewed and discussed in five sections concerning the effects of artificial production releases (supplementation) on wild fish population abundance, competitive social interactions, predation, health, and migratory behavior. Each section provides relevant conclusions drawn from the review.

Conclusions and Recommendations

The final section draws some overall conclusions from the completed reviews and analyses, and makes recommendations. It includes summary tables which detail an assessment of the potential effects of artificial production strategies on population abundance of wild spring/summer chinook and steelhead in their respective ESUs. In this section the authors conclude that hatchery strategies offer the potential to stabilize and amplify salmonid populations, but the artificial environment conditions salmonids to respond in ways different from fish reared in natural environments. Fundamental changes in the dynamics of hatchery production policy and implementation may be necessary both where hatchery supplementation is used to maintain some populations until underlying causes of decline are corrected, and where production hatchery operations overlap listed stocks. However, the overall effectiveness of supplementation to maintain a population until underlying causes of decline are corrected is unknown. Little specific numerical information exists regarding population abundance dynamics or interactive factors, therefore assessments can only be prescribed in directional trends rather than absolute values.

Finally, the authors conclude that the direction of future use of artificial propagation in the Columbia Basin will be a function of both the status of the natural populations and their habitats. For supplementation and recovery purposes, the productivity of naturally spawning populations will be a key parameter. Current information is not adequate to assess properly the potential effects of hatchery operations on wild stocks. The authors recommend that the Region should focus research to develop policies and procedures which properly integrate the roles of hatcheries for conservation and sustainability of salmonid populations. Artificial propagation risks may be ameliorated by development and implementation of conservation hatchery protocols which may improve fitness and survival of hatchery fish.

The report includes a bibliography of some 270 citations.

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