Artificial Selection and Environmental Change: Countervailing Factors Affecting the Timing of Spawning by Coho and Chinook Salmon

Abstract

Spawning date is a crucial life history trait in fishes, linking parents to their offspring, and it is highly heritable in salmonid fishes. We examined the spawning dates of coho salmon Oncorhynchus kisutch and chinook salmon O. tshawytscha at the University of Washington (UW) Hatchery for trends over time. We then compared the spawning date patterns with the changing thermal regime of the Lake Washington basin and the spawning patterns of conspecifics at two nearby hatcheries. The mean spawning dates of both species have become earlier over the period of record at the UW Hatchery (since the 1950s for chinook salmon and the 1960s for coho salmon), apparently because of selection in the hatchery. Countering hatchery selection for earlier spawning are the increasingly warmer temperatures experienced by salmon migrating in freshwater to, and holding at, the hatchery. Spawning takes place even earlier at the Soos Creek Hatchery, the primary ancestral source of the UW populations, and at the Issaquah Creek Hatchery. Both species of salmon have experienced marked shifts towards earlier spawning at Soos Creek and Issaquah Creek hatcheries despite the expectation that warmer water would lead to later spawning. Thus, inadvertent selection at all three hatcheries appears to have resulted in progressively earlier spawning, overcoming selection from countervailing temperature trends.

Straying of hatchery salmon in Prince William Sound, Alaska

“…One is that interbreeding can decrease the fitness of wild fish. For example, hatchery techniques can shift the timing of spawning (Quinn et al 2002), such that progeny from hatchery-wild mating do not spawn at an optimal time for reproduction (Ford et al 2006). A second concern is that hatchery straying into wild populations can reduce genetic diversity among wild salmon populations.…”

Behavioral Thermoregulation and Slowed Migration by Adult Fall Chinook Salmon in Response to High Columbia River Water Temperatures

“…Previous studies suggest that the timing of river entry and migration for anadromous salmonids is selectively adapted (Smoker et al 1998;Quinn et al 2000Quinn et al , 2002Stewart et al 2002;Keefer et al 2004b). And although some stocks, particularly steelhead, have some flexibility with which to react to prevailing river flow and temperature conditions (Robards and Quinn 2002;Keefer et al 2004a), flexibility in migration timing generally appears to be limited for salmonids.…”

Life-History Divergence in Chinook Salmon: Historic Contingency and Parallel Evolution

“…That divergent selection for run timing can lead to rapid evolutionary change in Pacific salmon has been well established (e.g., Flagg et al 1995;Quinn et al 2002). The evidence for widespread parallel evolution of run timing differences in Chinook salmon is of particular interest because run timing is closely tied to spawn timing, which in turn directly affects the degree of reproductive isolation.…”