Ongoing localized extinctions of stream-dwelling white-spotted charr populations in small dammed-off habitats of Hokkaido Island, Japan
Habitat fragmentation caused by damming can greatly reduce the population viability of aquatic organisms, with smaller fragmented populations at higher risk of extinction due to increased demographic, genetic, and environmental stochasticity. However, empirical evidence demonstrating that smaller natural populations are more vulnerable to extinction is limited. We studied the vulnerability to extinction of white-spotted charr (Salvelinus leucomaenis) populations in 30 dammed-off streams in Oshima Peninsula, southwestern Hokkaido Island, Japan, by comparing the incidence of charr populations in streams between 1999 and 2014. Using electrofishing and environmental DNA surveys, we identified three localized extinctions, with the probability of extinction increasing with decreasing watershed area (our surrogate for habitat size). We also found a new population in one dammed-off stream in which white-spotted charr were previously unknown, after installation of a fish ladder, indicating the capacity of white-spotted charr to recolonize reconnected habitat in a short period. Our results suggest that localized extinction of white-spotted charr in small dammed-off streams is ongoing, but that appropriate fish migration corridors can reduce localized extinction risk and increase the probability of species persistence.
KeywordseDNA Environmental stochasticity Isolation Population size Salmonid
We thank Steve O’Shea for editing a draft of this manuscript and Yukuto Sato for MiFish pipeline analysis. The electrofishing surveys were made possible by sampling permits issued by the Governor of Hokkaido. This study was supported by the Japan Society for the Promotion of Science KAKENHI Grant Numbers JP25450293(KM), 17H03623(HA), and in part by the Environment Research and Technology Development Fund (4-1602) of the Ministry of the Environment, Japan. MM was supported by JST CREST Grant Number JPMJCR13A2, Japan.
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