Premium
Hybridization between Spring‐ and Fall‐Run Chinook Salmon Returning to the Trinity River, California
Author(s) -
Kinziger Andrew P.,
Loudenslager Eric J.,
Hankin David G.,
Anderson Eric C.,
Garza John Carlos
Publication year - 2008
Publication title -
north american journal of fisheries management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.587
H-Index - 72
eISSN - 1548-8675
pISSN - 0275-5947
DOI - 10.1577/m07-103.1
Subject(s) - chinook wind , oncorhynchus , fishery , hatchery , spring (device) , fish <actinopterygii> , biology , mechanical engineering , engineering
It is believed that spring‐ and fall‐run Chinook salmon Oncorhynchus tshawytscha returning to the Trinity River, California, were once reproductively isolated such that spring‐run fish spawned upstream in early fall, whereas fall‐run fish spawned further downstream in late fall. However, construction of Lewiston Dam and the Trinity River Hatchery (TRH) in 1964 resulted in extensive compression of spawning habitat and the potential for inadvertent interbreeding of the two runs. In this study, we used genetic methods and developed a simulation procedure to assess the degree to which spring‐ and fall‐run Chinook salmon returning to TRH were genetically distinct and to determine the extent of hybridization between the runs. Approximately 40 adults/week were sampled throughout the 1992 spawning season, and all individuals were genotyped at 29 polymorphic loci. Analysis with the program STRUCTURE (Pritchard et al. 2000) supported the hypothesis that the data represented two subpopulations. Individual assignments using STRUCTURE indicated that the spring‐ and fall‐run proportions among fish sampled at TRH gradually shifted through time; weekly samples taken earlier in the spawning season had a higher proportion of presumptive spring run, and those taken later in the season had a higher proportion of presumptive fall run. Comparison of observed results with simulated data suggested the occurrence of hybridization between spring‐ and fall‐run Chinook salmon returning to TRH, particularly during the transition or overlap period between fish from the two phenotypic groups. The extent to which hybridization was caused by hatchery operations or occurred prior to Lewiston Dam construction was unclear. Additional hybridization analyses of samples collected prior to dam and hatchery construction would be needed to evaluate the impacts of these facilities on hybridization. Further, studies of contemporary populations are needed to determine whether two runs currently exist despite the marked hybridization that was documented herein for the 1992 return year.