58 DECEMBER 2023 • WORLD AQUACULTURE • WWW.WAS.ORG wild population by limiting the number of artificially produced adults on the spawning ground. It is becoming standard practice for hatchery programs to source eggs throughout the spawning run to avoid shifting natural spawn timing. These facilities include precocious two-year old (Jack) males in spawning to maintain natural age of maturation strategies within the population. Many hatcheries source water from the natural population’s water supply, which allows them to match natural temperature profiles and growth rates. This aids in reducing unintentional selection against thermal and size related adaptations on the ends of the trait bell curve. Although less commonly practiced, other techniques for retaining natural traits in artificially produced populations are available. Centralized incubation and rearing facilities using constant temperature pathogen free groundwater to enable transfers across fish health management zones can utilize chilling and heating to mimic local seasonal temperature profiles. Alternatively, to reduce energy costs, these facilities could be sited within local target basins or be replaced with local streamside incubation, rearing and acclimation facilities. Beyond temperature, to a limited degree, feed rations can be managed to match the population’s natural growth profile and precocity. Replacing artificial spawning with spawning channels should aid in maintaining naturally and sexually selected reproductive traits within a population. If population amplification requires additional culture, emerging fry can be collected from the channel and used to stock grow out facilities. Several imperiled species programs pioneered a more vigorous approach for retaining naturally and sexually selected traits by stocking every broodyear only with eyed eggs, parr or smolts collected from the target population’s natural spawning or rearing habitat (Maynard et al. 2012). In iteroparous species (those that spawn more than once), as in some steelhead trout and Atlantic salmon, live spawning, kelt (postspawned fish) conditioning, and release can be used to maintain iteroparity. Technology for holding captive anadromous populations in seawater during their ocean life history phase has been developed and should be considered for all captive rearing programs desiring the retention of anadromous traits (Maynard et al. 2012). This includes the development of ultrasound techniques for separating maturing fish needing transfer to freshwater from non-maturing fish requiring additional seawater rearing. This assists in reducing both unintended selection against age of maturation and timing of freshwater reentry. An aspect of seawater rearing needing further development is a technique for separating smolts from parr in populations with multiple outmigration windows to avoid unintended selection on alternate life history strategies. There are other culture practices, yet to be fully developed, that could be useful for avoiding unintended domestication selection. Among these are diets approximating prey protein, lipid and carbohydrate chemistry that will aid in reducing selection against natural digestive biochemistry. Techniques should be developed to separate out emerging sockeye salmon fry swimming in the wrong direction from those moving in the correct direction to reach the population’s natal rearing lake. Volitional release technology accommodating all smolt outmigration windows within a source population need to be developed. Finally, thought should be given to developing approaches to identify, collect and include yearling precocious males in the artificial spawning process. Conclusion Adopting approaches for maintaining natural traits in artificially cultured populations scheduled for return to the wild is crucial for program success. The success artificial culture programs have in developing self-sustaining natural populations will depend on their ability to maintain the population’s natural balance of polymorphic traits during captivity. Similarly, the negative impacts that integrated mitigation and enhancement programs have on neighboring natural populations will be lessened to the extent they maintain the natural balance of polymorphic traits within the cultured population. Reintroduction programs will benefit by sourcing fish from populations living in habitats with characteristics similar to their target reintroduction areas. Alternatively, they should source fish from populations with a wide array of polymorphic traits to provide natural selection the fodder needed to select traits best suited for the colonized environment. Reintroduction programs as well as all imperiled species recovery programs must aim to limit unintentional domestication selection during culture. In summary, culture tools have been developed to reduce unintended domestication selection and should be used, as practical, to meet program goals to maintain, build or reestablish self-sustaining natural populations. Notes Desmond J. Maynard Ph. D., Retired NOAA Fisheries Research Biologist, 9110 Phillips Road, Port Orchard, Washington 98367 Corresponding Author: desmondmaynard@msn.com References Beacham, T. D. and C. B. Murray. 1987. Adaptive variation in body size, age, morphology, egg size and developmental biology of Chum Salmon (Oncorhynchus keta) in British Columbia. Canadian Journal of Fisheries and Aquatic Sciences 44(2):244-261 Blouin, M. S., M. C. Wrey. S. R. Bollmann, J. C. Skaar, R. G. Twibell and C. Fuentes. 2021. Offspring of first-generation hatchery steelhead trout (Oncorhynchus mykiss) grow faster in the hatchery FIGURE 6. Illustration of multigenerational filling of egg incubation facilities prior to end of the annual run, shifting female ripeness earlier than that of the wild source population. The bell curves represent number of females ripening per day during the spawning season. The dotted vertical lines represent theoretical broodyear (BY) averages.
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