Genetic Risk Associated with Supplementation of Pacific Salmonids: Captive Broodstock Programs

We simulated some of the genetic consequences of temporarily using captive broodstocks to supplement Pacific salmon (Oncorhynchus spp.) populations. Results were summarized in terms of the parameter ΔIBD, which represents the change in level of inbreeding in the postsupplementation population compared with the control. We found that: (1) the most important factor affecting ΔIBD was whether the population remained large after supplementation ceased; (2) the absolute number of wild adults taken for broodstock had a stronger influence on ΔIBD than did the proportion of the population sampled; (3) if a captive broodstock program is successful, virtually all of the genes in the postsupplementation population will be derived from fish taken into the hatchery for broodstock; (4) in programs that last longer than one generation, marking hatchery fish is essential to avoid additional increases in inbreeding, and marking rates < 100% may be ineffective; and (5) broodstock practices such as sib-avoidance mating and equalizing progeny number affected inbreeding levels during the captive phase but had little permanent effect on ΔIBD. A number of factors not considered in this study (e.g., domestication selection and the fitness consequences of given levels of inbreeding) should also be evaluated in deciding whether or how to implement captive broodstock programs.