2025-04-03 カリフォルニア大学バークレー校(UCB)
<関連情報>
- https://news.berkeley.edu/2025/04/03/a-single-dry-winter-decimated-californias-salmon-and-trout-populations/
- https://www.pnas.org/doi/10.1073/pnas.2415670122
分布域の縮小の解剖学:流れと季節の不一致が分布域の端付近のサケ科魚類を脅かす Anatomy of a range contraction: Flow–phenology mismatches threaten salmonid fishes near their trailing edge
Stephanie M. Carlson, Kasey C. Pregler, Mariska Obedzinski, +5, and Mary E. Power
Proceedings of the National Academy of Sciences Published:March 31, 2025
DOI:https://doi.org/10.1073/pnas.2415670122
Significance
Learning how climate change alters distributions of organisms over the Earth is essential for predictive understanding. Do local populations dwindle as conditions grow more stressful, or are they abruptly extirpated? We need surveys with more spatial and especially temporal resolution to learn which climate-related factors threaten populations, and how various species, subspecies, and life history stages can respond. Here, we show in detail how a historically severe drought blocked access to critical breeding and rearing habitats for three native salmonids in rivers along the California North Coast. Different salmonids coped, not always successfully, by altering breeding timing or location. With site-specific, mechanistic understanding of hydroclimatic challenges to organisms, we can anticipate and mitigate these threats to valued natural populations.
Abstract
Climate change is redistributing life on Earth, with profound impacts for ecosystems and human well-being. While repeat surveys separated by multidecadal intervals can determine whether observed shifts are in the expected direction (e.g., poleward or upslope due to climate change), they do not reveal their mechanisms or time scales: whether they were gradual responses to environmental trends or punctuated responses to disturbance events. Here, we document population reductions and temporary range contractions at multiple sites resulting from drought for three Pacific salmonids at their ranges’ trailing edge. During California’s 2012 to 2016 historic multiyear drought, the 2013 to 2014 winter stood apart because rainfall was both reduced and delayed. Extremely low river flows during the breeding season (“flow–phenology mismatch”) reduced or precluded access to breeding habitat. While Chinook (Oncorhynchus tshawytscha) experienced a down-river range shift, entire cohorts failed in individual tributaries (steelhead trout, O. mykiss) and in entire watersheds (coho salmon, O. kisutch). Salmonids returned to impacted sites in subsequent years, rescued by reserves in the ocean, life history diversity, and, in one case, a conservation broodstock program. Large population losses can, however, leave trailing-edge populations vulnerable to extinction due to demographic stochasticity, making permanent range contraction more likely. When only a few large storms occur during high flow season, the timing of particular storms plays an outsized role in determining which migratory fish species are able to access their riverine breeding grounds and persist.
