Release of Captively Reared Adult Anadromous Salmonids for Population Maintenance and Recovery: Biological Trade-Offs and Management Considerations
Barry Berejikian, Thomas Flagg, and Paul Kline
Abstract.—Captive broodstocks have been initiated for maintenance and recovery of imperiled anadromous salmonid populations because they can provide a rapid demographic boost and reduce short-term extinction risk. As with captive propagation programs for other vertebrates, difficulties with reintroduction to the natural environment may impede success in achieving the program’s objectives. Strategies for reintroduction of anadromous salmonid captive broodstocks in the United States and Canada include release of captively reared adults (currently four programs), stocking their offspring as eyed eggs (two programs), parr (six programs), or smolts (nine programs). Captive broodstock programs that release adults considered the management objectives of (i) evaluating of different reintroduction strategies, and (ii) spreading the risk of failure of any one particular strategy to be much more important than programs that do not release adults. This distinction indicates that the programs releasing adults consider the strategy to be an experimental one that may serve to offset potential risks associated with juvenile release options. However, the finding that preventing extinction was considered to be very important in adult and juvenile release programs alike indicates that programs releasing adults believe the strategy, at a minimum, will not impede that objective. We summarized the salmonid literature on (1) natural and sexual selection during reproduction, (2) homing and straying, (3) rearing effects on social behavior, (4) domestication, and (5) survival as it relates to biological trade-offs of different reintroduction strategies for captive broodstocks. The adult release strategy provides potential biological benefits that include the opportunity for natural and sexual selection to occur on the spawning grounds—selection that is relaxed during artificial spawning. Adult release and egg stocking may reduce potential for unnaturally high straying rates and may minimize domestication selection of the offspring compared to programs that artificially spawn adults and release their offspring as smolts. The potential benefits of adult and egg releases must be weighed against (and may be offset by) the greater F1 production that could be achieved by releasing hatchery-reared smolts. A variety of reintroduction strategies will likely continue to be appropriate for captive broodstock programs.