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UCREFRP
UCREFRP Catalog Number
9514
Author
Waples, R. S.
Title
Dispelling Some Myths about Hatcheries
USFW Year
1999
USFW - Doc Type
Fish Culture-Perspective
Copyright Material
YES
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<br />. Whether, on average, hatchery fish stray more fre- <br />quently than natural fish is an open question. Studies of <br />straying in natural populations have been too limited to <br />resolve this issue. <br />. Homing and straying are complex phenomena that <br />are imperfectly understood. Fish culture can be a factor in <br />the level of straying, but stock transfers and choice of <br />release site also can have a strong influence. Programs that <br />involve translocated stocks can lead to straying on a geo- <br />graphic scale much greater than would occur naturally. <br />. Effects on natural populations are a function of the <br />proportion of natural spawners that are hatchery fish, not <br />the fraction of the hatchery population that strays (Grant <br />1997). Therefore, a hatchery program with a relatively low <br />stray rate can still substantially affect natural populations, <br />particularly if the hatchery is large and/ or the natural <br />populations are depressed. Conversely, a relatively high <br />stray rate from a small hatchery might not substantially <br />affect a large natural population. Furthermore, the genetic <br />impact of stray hatchery fish can be less than their num- <br />bers would indicate if they have reduced reproductive <br />success in the wild. <br /> <br />Corollary 2: Hatchery fish will transfer disease and <br />parasites to natural populations. <br />It is by no means inevitable that such transmission will <br />take place. For example, although several pathogens are <br />abundant and cause chronic problems in Pacific salmon <br />hatcheries, little or no direct evidence exists of transfer <br />from cultured to natural populations in spite of apparent- <br />ly widespread opportunities for this to occur. That these <br />diseases also are endemic to natural populations, which <br />appear to have evolved strategies for dealing with them, is <br />probably a factor in this result. A cautionary note is that we <br />have relatively little information about the incidence of dis- <br />ease in natural salmon populations and almost no historical <br />information about pristine populations. Therefore, it is diffi- <br />cult to be sure that salmon hatcheries have not contributed <br />to the current pathogen levels in natural populations. <br />In contrast, clear evidence exists that stock transfers of <br />fish can lead to the spread of exotic pathogens and para- <br />sites into natural fish populations well out of the historic <br />range of the disease. In two recent examples [spread of <br />Gyrodactylus salaris into populations of Atlantic salmon (Sal- <br />mo salar) in Norway and spread of whirling disease (Myxo- <br />bolus cerebralis) into populations of rainbow trout (Oncor- <br />hynchus mykiss) in several areas of the western United <br />States], pathogens were brought into contact with natural <br />populations that had no previous exposure to them, in each <br />case with devastating results. Stock transfers of Atlantic <br />salmon and rainbow trout, respectively, appear to have <br />been involved in the spread of these two diseases. Even in <br />these cases, however, the exact nature of the link with <br />hatchery propagation may not be clear. For example, the <br />recent appearance of whirling disease in Montana, which <br />does not currently have a trout stocking program, suggests <br />that factors other than artificial propagation (e.g., anglers, <br />their boats or equipment, or fish-eating birds) may have <br /> <br />February 1999 <br /> <br />FISH CULTURE-PERSPECTIVE <br /> <br />contributed to the spread of this pathogen, at least in that <br />state (Bergersen and Anderson 1997; Potera 1997). <br />Recent efforts in many areas to limit the number and <br />geographic scale of stock transfers of fish should help <br />reduce the risk of disease transmission to natural popula- <br />tions, but (as is apparent from the above example) vigi- <br />lance on other fronts is necessary as well. <br /> <br />Myth 4: Objections to hatcheries are purely theoretical <br />and have no empirical basis. <br />This has been a theme of some recent pieces complain- <br />ing about critics of hatcheries (e.g., Incerpi 1996; Rensel <br />1997). I don't believe this view is supported by a review of <br />the evidence. It is true that our understanding of the <br />genetic and ecological effects of hatcheries on natural pop- <br />ulations is far from perfect. Substantial uncertainties <br />remain about virtually every major issue, and periodically <br />it is important, as Campton (1995) has done, to take stock <br />of the situation and summarize the empirical data to help <br />refocus the debate. Nevertheless, I believe a review of this <br />body of information shows that, in spite of the many <br />uncertainties, every major concern raised about hatcheries <br />has some empirical basis. Extensive literature exists on this <br />topic (e.g., see Waples 1991; Hindar et al. 1991; Campton <br />1995 and other papers in the same volume), but I will give <br />a few more recent examples. <br />. For several decades, Washington State has used a <br />management strategy for winter steelhead (0. mykiss) that <br />involves advancing the run timing of hatchery popula- <br />tions by several months (Crawford 1979). Although initial- <br />ly designed to allow production of yearling smolts, the ad- <br />vancement in run timing is now viewed as a fisheries <br />management tool that minimizes opportunities for inter- <br />breeding with natural fish and allows selective harvest of <br />hatchery fish. The program is based on a few domesticat- <br />ed stocks that are widely distributed throughout the state. <br />In a comprehensive allozyme study of steelhead popula- <br />tions in Washington State, Phelps et al. (1994) found evi- <br />dence for introgression of the nonnative hatchery stock into <br />a number of natural populations but found no evidence of <br />introgression in other populations. The fitness consequences <br />of the interbreeding have not been critically evaluated. <br />. In an analysis of spawner-recruit relationships for 26 <br />steelhead populations in Oregon, Chilcote (1997) found a <br />strong negative correlation between the proportion of nat- <br />urally spawning hatchery fish and stock productivity. Al- <br />though this correlation is striking and suggests that hatch- <br />ery fish may be depressing fitness of natural populations, <br />it does not necessarily represent a causal relationship since <br />other factors (e.g., larger hatchery programs in areas where <br />freshwater habitat cannot support healthy natural popula- <br />tions) may have influenced the results. Chilcote did not <br />find a relationship between stock origin and productivity. <br />. In the Tucannon River in southeastern Washington, a <br />supplementation program for the depressed run of spring <br />chinook salmon (0. tshawytscha) was initiated in the mid- <br />1980s. Founded with local broodstock, this program aims <br />to maintain genetic integrity of the natural population and <br /> <br />Fisheries" 17 <br />
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