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Politics and pride: Maintaining genetic novelty may be detrimental for the conservation of Formosa landlocked salmon Oncorhynchus formosanus
- Burridge, Christopher Paul
- Aquatic conservation 2019 v.29 no.5 pp. 840-847
- Oncorhynchus masou, altitude, freshwater, genetic factors, genetic rescue, genetic variation, guidelines, inbreeding, phenotype, politics, risk, salmon, streams, taxonomy, testcrosses, Taiwan
- Populations of conservation concern are often rare, restricted in range, and isolated from other populations. This can manifest in low genetic diversity, which reduces the ability of a population to respond to changes in the environment, and in higher levels of inbreeding, which reduce individual fitness. Isolated populations, however, often harbour genetic and phenotypic novelty, which can elicit a strong community sentiment to maintain these populations. Genetic rescue – the introduction of genetic variation to improve fitness – offers potential benefits for isolated and threatened populations, but has associated risks, including a perceived loss in identity if that population is geographically, genetically, and culturally significant. Here, the potential benefits and risks of genetic rescue for isolated freshwater populations are discussed, using the Formosa salmon as an exemplar. Formosa landlocked salmon, a member of the masu salmon complex (Oncorhynchus masou sensu lato), is the southernmost naturally distributed salmonid in the world, occupying a single stream at high elevation in Taiwan. Listed as Critically Endangered, it exhibits continuing low abundance (<5000 individuals). Although Formosa salmon can be genetically distinguished from other masu salmon, its genetic variation is extremely low and genetic factors may now critically affect fitness. There appears to be clear merit for the genetic rescue of Formosa salmon, and test crosses involving other landlocked masu salmon are urgently required. If these test crosses yield individuals of high fitness, guidelines for introductions into the wild are provided. In addition, subpopulations above and below artificial instream barriers to movement require connection via the direct exchange of individuals to minimize any further losses of genetic variation. Insurance populations with independent risk probabilities to the existing population should also be constructed, with continuing connectivity among populations through the direct exchange of individuals.