Genetic and Phenotypic Variation through the Migratory Season Provides Evidence for Multiple Populations of Wild Steelhead in the Dean River, British Columbia

Abstract

We provide evidence for previously undetected population structure in a wild run of summer steelhead Oncorhynchus mykiss within a river that has considerable recreational importance (Dean River, British Columbia). Data were gathered from an existing catch‐and‐release fishery and examined for phenotypic and genetic variation through the migratory season. Specifically, we compared fish captured in different periods during the migration: early (July 2‐30), middle (July 31‐September 5), and late (September 6‐30). Age (freshwater and saltwater), sex ratio, and body girth did not differ significantly among these groups for females or males. Body length increased through the migratory season for both sexes, perhaps because late‐migrating fish had more time to feed in the ocean. Based on genotypes at 10 microsatellite loci, early and late groups showed highly significant genetic differences (P < 0.001). Assignment tests were able to classify individuals back to early or late groups with 84% accuracy (122 of 145 tests). These results suggest the presence of at least two populations that migrate at different times in the Dean River system. The magnitude of the genetic difference was small (FST = 0.007; Nei's unbiased D = 0.0149, Reynolds coancestry coefficient = 0.007) but comparable to values for other anadromous Pacific salmon species over similar spatial scales. Moreover, the coarse level of our sampling, and possible overlap in migratory timing among populations, suggests that the observed differentiation underestimates the true differentiation. A deficit of heterozygotes in the late group suggests further population substructure within late‐migrating groups of fish. Examining temporal variation through a migratory season proved a useful approach for obtaining preliminary evidence of population structure in migrating salmonids within a small river system.

Genetic Diversity in Steelhead before and after Conservation Hatchery Operation in a Coastal, Boreal River

“…Average expected heterozygosities of 0.51-0.61 in the Kitimat River steelhead year-classes are consistent with values reported for steelhead and rainbow trout from other regions in BC (Beacham et al 2000;Heath et al 2001;Hendry et al 2002;Taylor and Tamkee, unpublished) and in other portions of the species range (e.g., Beacham et al 1999;Knudsen et al 2002;Taylor and Tamkee, unpublished).…”

“…Steelhead (anadromous rainbow trout Oncorhynchus mykiss) is an ecologically variable species (Behnke 1992) and shows considerable genetic variation among populations (Busby et al 1996;Beacham et al 1999;Heath et al 2001Heath et al , 2002Hendry et al 2002). Steelhead from the western coast of North America have been widely stocked and naturalized throughout the world.…”

Relative contributions of neutral and non‐neutral genetic differentiation to inform conservation of steelhead trout across highly variable landscapes

“…; Zimmerman and Reeves ; Hendry et al. ; Matala et al. ), and address some local conservation concerns.…”

Non‐direct homing behaviours by adult Chinook salmon in a large, multi‐stock river system

“…Extensive migrations and precise homing to natal sites are fundamental to the life histories of anadromous salmonids ( Oncorhynchus and Salmo species). Philopatry to natal river systems and even to specific spawning reaches (Quinn et al , 1999; Bentzen et al , 2001) is a distinctive trait that allows adaptation to local conditions and substantial phenotypic, genetic and behavioural variation within species (Quinn et al , 2000; Beacham et al , 2002; Hendry et al , 2002). Adult salmonid homing has been clearly linked to olfactory imprinting on chemical cues in home waters (Hasler & Scholz, 1983), and detection and response to chemosensory cues is believed to at least partially guide adult homing through migration corridors (Quinn et al , 1989; Keefer et al , 2006).…”