Every year, rivers of chinook—the Pacific's largest salmon—leave the ocean for an upstream trek into the streams of their birth. When these 4-to-6-year-olds reach home, they spawn and die. Surprisingly, a new study finds, most of the moms in one of Washington State's major spawning populations appear to have begun their lives as males.
"This is clearly abnormal," notes James J. Nagler, a fish reproductive biologist at the University of Idaho in Moscow. The findings that he and his colleagues reported late last week worry several environmental scientists.