A landmark genetic study has concluded that spring-run and fall-run Chinook salmon are “fundamentally the same animal,” a conclusion with important implications for salmon recovery efforts and regional economics.
“It’s like blue and brown eye color in humans — it just depends on what genotype you inherit from your parents,” said study co-author John Carlos Garza, adjunct professor of ocean sciences at UC Santa Cruz and a research geneticist with NOAA’s Southwest Fisheries Science Center. The new findings were published in the Oct. 29 edition of Science.
Genetic sequencing of Chinook salmon carcasses in southwest Oregon’s Klamath Basin found that spring-run and fall-run salmon were freely interbreeding. “In other words, a spring-run salmon can have a fall-run sibling,” UC Santa Cruz said in an online article. (news.ucsc.edu/2020/10/chinook-salmon.html)
Whether a Chinook salmon returns in the spring or fall is determined by a single small region on chromosome 28. “That was an extraordinary finding,” Garza said. “I know of no other gene region that so completely determines a complex migratory behavior in the wild in a vertebrate.”
Spring-run and fall-run fish all start maturing at the same time in the ocean, but the ones with the spring-run gene are caught by humans earlier in their maturation process than fall-run fish, leading to a higher fat content and other physical differences.
The lack of difference between runs has “profound implications for conservation and management of Chinook salmon,” researchers said, making restoration efforts more straightforward.
Spring Chinook have long been considered the premium gourmet salmon preferred by humans and orcas, while later-arriving Chinook are a key recreational fishery.