Genetic insights into the past, present, and future of a keystone species

In a new paper in PNAS, Thompson et al. (1) examine the genetic legacy of a struggling keystone species—and the implications for a phoenix-like recovery from its genetic remnants. For thousands of years before European contact, indigenous peoples of the Pacific Northwest of North America eagerly anticipated a critical spring event: the return migration of Chinook salmon (Oncorhynchus tshawytscha) into freshwater (Fig. 1). Early-migrating Chinook travel farther upstream than typical fall-migrating Chinook and are highly valued for their superior nutritional value and for providing an influx of protein and fat during a critical period (2). The importance of these salmon is highlighted by numerous traditional celebrations and ceremonies that mark their return. Colonizing Europeans also valued these early-returning salmon, which were heavily harvested, so much so that they began to show signs of depletion as early as the 1870s in the Columbia River (3, 4). Early-migrating Chinook also played an important role in terrestrial ecosystems by providing predators with longer access to salmon resources and transporting marine-derived nutrients farther upstream—and earlier (3). It is safe to say that these early-migrating salmon, or “spring Chinook,” were a keystone species for peoples and ecosystems.

However, this is no longer the case. Human activities, including extensive dam construction, fishing, and water diversion for agriculture, have caused wide-spread population declines and the loss of an estimated 54% of spring Chinook populations from the contiguous United States (5). In US endangered species legislation, spring Chinook populations are usually not considered separately from fall Chinook populations within the same watershed (6). In some watersheds, struggling spring Chinook populations are not listed because their fall counterparts are abundant. Spring Chinook …

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