Evaluation of a trap-and-transport program for a threatened population of steelhead (Oncorhynchus mykiss)

Trap-and-transport programs for migratory fish attempt to mitigate for lost habitat blocked by impassable dams. These programs aim to assist with conservation and recovery of declining populations by accessing habitat protected from impacts downstream, such as introgression or competition with hatchery-origin fish. This study examined a trap-and-transport program that supplemented a native population of winter-run steelhead (Oncorhynchus mykiss) above Foster Dam in the South Santiam River, Oregon. The study examined whether outplanted adults transported from 2012 to 2016 reproduced successfully using 268 single nucleotide polymorphisms (SNPs) and an exclusion analysis in CERVUS. Genotypes from two SNPs in the GREB1L gene were used to associate each fish with maturation at return migration: premature migration (summer-run, non-native) or mature migration (winter-run, native). Parentage analyses demonstrated that 51% of outplanted steelhead successfully produced either juvenile or adult offspring. More than 68% of the natural-origin adults outplanted during the study were homozygous for mature migration alleles that are typical of native, winter-run steelhead, however, potential introgression from non-native, summer-run steelhead was detected in 26% of the outplanted adults. These results indicate that transported adult steelhead successfully produced juvenile and adult steelhead, and introgression associated with non-native steelhead may be introduced through the trap-and-transport program.