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AN AUGMENTATION PLAN FOR RAZORBACK SUCKER tions and a stocking evaluation plan. The failure of these reintroduction efforts indicated that the con- tinued decline of the razorback sucker is not solely a problem of stocking, but probably a wider prob- lem associated with environmental changes. Thus, any stocking program to reintroduce the razorback sucker must be complimented with some form of habitat enhancement. After the habitat has been enhanced to allow razorback sucker recruitment, the decision of whether or not to stock should be made relative to genetic and demographic criteria. The question of when to initiate stocking is linked with how many individuals are necessary to persist, i.e., population viability (Salwasser et at. 1984). The often-used numbers of individuals necessary to maintain suffi- cient genotypic variation in order to avoid inbreed- ing depression and genetic loss due to drift have been 50 and 500, respectively (Franklin 1980). Al- though this recommendation for short- and long- term variation has been widely cited (Simberloff 1988), these criteria were intended only as guide- lines. The lower number was based on agricultural breeding guidelines that allow 1% loss of heterozy- gosity per generation and the higher number on loss of alleles within a single-locus trait in the absence of selection in a single species (Drosophila). Lande (1988) suggested that more complicated genetic variation may require larger populations to prevent losses due to drift. Boyce (1993) stated that the 501500 rule was arbitrary and capricious and indi- cated that very few empirical studies define the size of a minimum viable population. Several bird pop- ulations of approximately 200 individuals have per- sisted through time (Thomas 1990). Despite the variation in the numbers suggested for minimum viability, there appears some uniformity among rec- ommendations in the order of magnitude between 100 and 1,000 individuals (Thomas 1990). Within this range, variation in species responses and the inability of current science to predict persistence leaves managers with no useful management rules (Simberloff 1988). Despite concern for genetic variation and the ability of a population to adapt to environmental changes, Lande (1988) suggested that most popula- tions become extinct due to demographic rather than genetic factors. He stated that demographic and environmental stochasticity are highly inte- grated. Similarly, Boyce (1992) concluded that de- mographic modeling is more likely to be of practical significance in determining viability. Thus, sufficient numbers of individuals need to exist to ensure growth and survival of a population. Environmental 107 factors are important in determining reproductive success, growth rates, and thereby, survival. It is demographic collapse that results in population de- clines that cause lack of genetic variation (Rabb and Lacey 1990). Because of the high longevity of ra- zorback sucker (McCarthy and Minckley 1987), de- mographic stochasticity is tempered against rapid fluctuations in generation size. Therefore, given representation of most age-classes, a smaller popu- lation of razorback sucker would be needed to pro- vide demographic stability than would be needed by a shorter lived species. In an effort to integrate genetic and demographic criteria, a process will be used to assist in deciding whether or not to stock razorback sucker (Figure 3). The logic presented assumes that habitat restora- tion or enhancement has been accomplished to sup- port the numerically depressed population. A pop- ulation size of 250 is arbitrary, but serves as a guideline for the lowest number that represents genetic viability. If it is assumed that the effective population size, N. (Wright 1931; Kimura and Crow 1963), is approximately 0.2 of a natural stock (Mace and Lande 1991), a total population of 250 should approximate an effective population size of 50 (Mace and Lande 1991). If a natural population has greater than 250 individuals and is successfully spawning and recruiting, then sufficient genetic vari- ation should exist to prevent inbreeding depression and stocking should not be initiated. Rather, man- agement resources should be directed toward hab- itat rehabilitation or enhancement to remove exist- ing environmental constraints and improve the existing dynamics. If a population exists that has greater than 250 individuals and is not recruiting but maintains a locally adapted genetic stock, stock- ing should be avoided until genetic risk to that population can be assessed and an appropriate course of action defined. The accumulation of na- tive broodstock will be necessary to provide a broodstock for reintroduction if natural recruitment cannot be attained. The introduction of fish from outside the local stock could potentially establish a population that replaces the local genome. If a population is functionally extirpated (i.e., no oppor- tunity for recovery), and the habitat provides the carrying capacity and necessary conditions for sur- vival, then stocking should be initiated. Determina- tion of the stock used to support reintroduction should represent those genotypes that evolved un- der the most similar environment, i.e., nearest neighbor population. Stocking should be termi- nated once natural recruitment has been renewed, but monitoring should be continued.