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FISH CULTURE-PERSPECTIVE Myth 2: Risks posed by hatcheries can be avoided with better management. This myth contains a good deal of truth. Considerable improvements have been (and continue to be) made in both fish culture and fisheries management, including bet- ter broodstock collection and mating protocols, more-nat- ural rearing conditions, wild-fish-friendly release strate- gies, and more focus on local broodstocks (Kapuscinski and Miller 1993; Maynard et al. 1995). Doubtless, these changes can help reduce opportunities for direct and indi- rect effects on natural fish populations; the myth is that these changes will make the problems disappear altogeth- er. This is an illusion for two reasons: (1) Genetic changes in cultured populations cannot be avoided entirely and (2) many risks are negatively correlated, so efforts to reduce one risk simultaneously increase another. Because this myth is central to the controversy regarding hatch- eries, I will consider it in some detail. Genetic changes in hatchery populations are associated with the terms domestication and domestication selection, which have been used in various (and sometimes confus- ing) ways in the literature. I'll offer definitions for these terms here, not because these definitions are necessarily the best, but because doing so should help clarify the A Hatchery v Wild Environments Similarities Differences . Water . Food . Photoperiod . Substrate . Density . Temperature . Flow regime . Competitors . Predators B Relative survival . Hatchery DWild -I ) I o Egg-smolt Smolt-adult Life stage Figure 1 illustrates two reasons why some genetic change relative to the wild population is inevitable as a result of fish culture. A. The selective regime experienced by hatchery fish differs in many impor- tant respects from that experienced in the wild (after R. Reisenbichler, u.s. Geological Survey, Seattle, unpublished data). B. The mortality profile in cultured fish populations differs dramatically from that expe- rienced in the wild, both before and after release from the hatchery (schematic diagram after Waples 1991). 14 + Fisheries discussion that follows. Although some definitions of domestication focus on adaptation to a human-controlled environment (e.g., Kohane and Parsons 1988), it can be useful to define the term more broadly to include any genetic changes that result directly or indirectly from human efforts to control the environment experienced by a population. Domestication thus describes a state or con- dition of a population and can be contrasted with the term domestication selection, which refers to a process that leads to domestication. Campton (1995) identified three factors that lead to genetic change in cultured populations: (1) intentional or artificial selection for a desired trait (such as growth rate or adult body size), (2) selection resulting from nonrandom sampling of broodstock, and (3) unintentional or natural selection that occurs in the hatchery environment. Camp- ton used the term artificial selection (selection due primarily to humans) to distinguish factors 1 and 2 from factor 3, which is the only one he considered to represent domesti- cation selection. Busack and Currens (1995) also recog- nized the same three factors but considered all to be forms of domestication selection. The distinctions made by Campton can be useful to separate human and environmental causes of genetic change; however, it also is important to remember that the overall effects on cultured and natural populations are the same regardless of how the components are categorized. For the latter reason, I favor the approach by Busack and Currens because it includes a broader range of factors under a single term. In fact, I would go further and identi- fy a fourth component of domestication selection: (4) tem- porary relaxation during the culture phase of selection that otherwise would occur in the wild. Busack and Currens considered this to be a component of their factor 3, but it can be useful to identify this factor explicitly. Temporary relaxation of selection may not lead to genetic change within the hatchery population, but it does lead to genetic change compared with the high mortality (some random deaths, but others selectively mediated) in the early life history phases in natural populations. Taking all of these factors into consideration, I define domestication selection as any change in the selection regime of a cultured popula- tion relative to that experienced by the natural population. Although it may be possible to eliminate intentional selection from hatchery programs, it generally will not be possible to eliminate factors 2-4 entirely because of two inescapable facts: (1) The hatchery environment differs in many ways from the natural environment, and (2) a suc- cessful hatchery program profoundly changes the mortali- ty profile of the population and results in more fish sur- viving than would have survived in the wild (Figure 1). Because of these factors, Busack and Currens (1995) con- cluded that some level of domestication selection is inevitable in a captive population. Although many factors can help reduce the nature and extent of the resulting genetic changes, they cannot be avoided entirely. There are several corollaries to the myth regarding domestication. Vol. 24, No.2