Biochemical Genetic Detection of Natural and Artificial Hybridization of Chinook and Coho Salmon in Northern California

Abstract

Allelic products of seven isozyme loci were used to identify presumptive hybridization between chinook salmon Oncorhynchus tshawytscha and coho salmon O. kisutch in northern California. First‐generation hybrid salmon (N = 3) were observed in samples from a tributary creek to the Trinity River; from rearing ponds at Camp Creek, a tributary to the Klamath River (N = 14); and from the ocean salmon fishery near Eureka (N = 2). The sample from the Camp Creek rearing ponds consisted of progeny from an inadvertent cross of coho and chinook salmon by hatchery personnel at the Irongate Hatchery. In addition to the artificial production of hybrid salmon at Irongate Hatchery, the alteration of traditional salmon spawning routes by Lewiston Dam on the Trinity River may have lead to natural hybridization between chinook and coho salmon in Deadwood Creek. Accurate quantification of the occurrence of hybridization was impossible due to nonrandom sampling of populations, but we presume to have underestimated the actual hybridization between these two species.

Sockeye salmon repatriation leads to population re‐establishment and rapid introgression with native kokanee

“…The unintended introgression of hatchery stock within other resident populations has occurred as the result of other Pacific salmon translocations (Bartley, Gall, & Bentley, 1990;Hess et al, 2011;Spies et al, 2007;Utter, 2000). In some instances, when this introgression was between populations with divergent life histories, outbreeding depression has been demonstrated (Gharrett, Smoker, Reisenbichler, & Taylor, 1999;Gilk et al, 2004).…”

Introgressive hybridization in fishes: the biochemical evidence

“…Thus in both cases further study would appear likely to reveal that they are of common occurrence. In contrast, the single occurrence of chinook (Oncorhynchus rshuyytscha) and coho (0. kisutch) salmon hybridization detected in a California river (Bartley et al, 1990) would seem a rare event. In spite of the extensive electrophoretic surveys of Pacific salmonid populations, no other natural hybrids have been detected biochemically between these species.…”

Chinook and Coho salmon hybrids linked to habitat and climatic changes on Vancouver Island, British Columbia

“…Natural hybridization between Chinook ( Oncorhynchus tshawytscha ) and Coho salmon ( Oncorhynchus kisutch ) has been documented but is rare (Bartley et al, 1990; Chevassus, 1979; Johnson & Ringler, 1981). Its infrequency has been attributed to prezygotic isolation mechanisms that prevent viable development (Bartley et al, 1990).…”

“…Natural hybridization between Chinook ( Oncorhynchus tshawytscha ) and Coho salmon ( Oncorhynchus kisutch ) has been documented but is rare (Bartley et al, 1990; Chevassus, 1979; Johnson & Ringler, 1981). Its infrequency has been attributed to prezygotic isolation mechanisms that prevent viable development (Bartley et al, 1990). Utter et al (1989) found no evidence of Chinook–Coho salmon hybrids in a Chinook salmon population structure study of 86 collection sites from the Babine River in British Columbia to the Sacramento River in California.…”

“…These factors place salmon at risk of "reverse speciation" and introgression, as environmental change weakens ecologically mediated reproductive isolation (Owens & Samuk, 2020). Negative consequences of introgression include outbreeding depression, lower performance in parental environment for traits such as feeding and predator avoidance (Wessel et al, 2006), early life history mortality (Bartley et al, 1990), and susceptibility to infectious diseases (Hedrick et al, 1987). In summary, highly hybridized populations have an elevated risk for extirpation or extinction (Rhymer & Simberloff, 1996).…”