Review : bird predation of juvenile salmonids and management of birds near 14 Columbia Basin dams Public Deposited


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Abstract or Summary
  • Bird predation of juvenile salmonids and/or bird predation control are reviewed for 14 of the 18 mainstem dams on the Columbia and Snake Rivers, but there was little information for some of these dams. California gulls, ring-billed gulls, Caspian terns, double-crested cormorants, American white pelicans, and several other bird species have been reported as predators of juvenile salmon and steelhead at these dams. Most estimates of the amount of this predation have been 2% or less of salmonids passing a dam. This is less than the percentage of juvenile salmonids killed during dam passage, and it has not been determined what proportion of salmonids taken by birds were already dead or mortally injured from dam passage. Thus, it is not clear what portion of bird predation is of viable salmonids that would have otherwise survived. Further, it appears that most juvenile salmonids in the Columbia Basin are not federally listed as threatened or endangered, so it is not known what impact bird predation at dams may have on listed salmonids. Nevertheless, predation may significantly affect certain salmon stocks, so it cannot be dismissed as unimportant. Bird management includes installing wires above the water at dam tailraces. Closely spaced wires are effective in keeping out flying birds. However, not all areas where birds feed on fish below dams can be covered with wires, the wires have sometimes been placed too far apart to keep out flying birds, and nonflying birds can go under wires. Consequently, Wildlife Services (which was known as Animal Damage Control prior to 1998) of the U.S. Department of Agriculture has also nonlethally harassed and lethally taken birds at dams after it has been requested to do so. Studies by staff of the U.S. Army Corps of Engineers have shown that nonlethal and lethal control by Washington Wildlife Services at The Dalles and John Day Dams needed to be repeated because birds would return. During 1997-1998, Wildlife Services dispersed at least 20,682 birds (mostly gulls) and lethally took at least 3,143 birds at these two dams. Most juvenile salmonids migrate past dams from April through early June, although many subyearling chinook migrate during July and August. Thus, bird control to protect juvenile salmonids would be most effective during April-July and perhaps through August for subyearling chinook. Beginning in August, many juvenile American shad are also migrating over lower Columbia dams and then can be more abundant than migrating salmonids; however, few shad pass Snake River dams and at least one mid-Columbia dam. Washington Wildlife Services' bird control has been during April-September at mid-Columbia dams and apparently during spring through winter at lower Columbia dams, so its control may sometimes occur when few juvenile salmonids are migrating. Although bird management at some dams has occurred since at least 1992, it has not yet been determined if this control is cost effective (i.e., the costs of bird control are less than the costs of predation). Washington Wildlife Services asserts that the cost of bird predation can be estimated by the cost of controlling predation. With this circular logic, Wildlife Services could spend a considerable amount of taxpayer or electric ratepayer money controlling predators that may be taking an insignificant number of viable juvenile salmonids and justify doing so because it has spent so much money. Consequently, it is important for there to be realistic evidence for the need or benefits of predator control, so that control is cost effective. Washington Wildlife Services has not been forthcoming in answering general questions about its activities at Columbia Basin dams and asserts that a federal Texas court case precludes disclosure of information. However, it seems that Wildlife Services may be using that court case to avoid scrutiny because the court ruled that Wildlife Services not provide information that could identify cooperators with Wildlife Services, not that it withhold all information about its activities. Further, Wildlife Services appears to have violated this court decision by providing other agencies with reports of its predator control activities that identifies specific cooperators, so Washington Wildlife Services seems to have selectively chosen when to use the court ruling as an excuse to not give out general information. Fish-eating bird control has proceeded very differently in the Columbia Estuary than at Columbia Basin dams. In the Estuary, bird predation was quantified in 1997 to establish a need for bird control; agency, tribal, and public consultations about a management plan were conducted, management actions began to be implemented in 1999, and predation reduction began to be quantified in 2000. At dams, Washington Wildlife Services assumed bird predation to be significant, initiated bird management before the amount of predation was measured, appears to have done less consultation with the public, other agencies, or tribes about its management actions; and assumed that its predator control actions have significantly reduced predation.
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  • Bayer, R. D. 2003. Review: Bird Predation of Juvenile Salmonids and Management of Birds Near 14 Columbia Basin Dams. Yaquina Studies in Natural History No. 10.
Table of Contents
  • Abstract -- Acknowledgments -- Preface -- Table of Contents -- Chapter 1. Introduction -- Chapter 2. Assumptions about Bird Predation and Management near Columbia Basin Dams -- Chapter 3. Methods of Controlling Fish-eating Birds -- Chapter 4. Introduction to Washington Wildlife Services' Control of Fish-eating Birds in the Columbia Basin -- Chapter 5. Fish-eating Bird predation and Management near Columbia Basin Dams -- Chapter 6. Discussion of Predation and Predator Control Near Columbia Basin Dams -- Appendix I. Common and Scientific Names of Animals Cited in This Report -- Appendix II. Background of Animal Damage Control and Wildlife Services -- Appendix III. Copy of Woodruff (2002) -- Literature Cited
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