Alaskan Salmon Evolve Along With the Climate Researchers have suspected that temperature-driven changes in migration and reproduction behaviors - which have happened in many species - may be evidence of natural selection at work. Now there is genetic evidence to confirm the hypothesis. For their study, published online last week in Proceedings of the Royal Society B, the scientists studied Alaska pink salmon in a small stream near Juneau where there have been complete daily counts of all adult fish since 1971. The salmon migrated in two distinct populations, one appearing toward the end of August, the other starting in September. In 1979, scientists introduced a neutral genetic marker into the later-migrating population so it could be identified and tracked without affecting its fitness. In the 1980s, the genetically marked late migrators made up about a third of the population. But as streams started warming earlier in the year, the proportion began to decrease rapidly - to just 5 percent by 2011 - even though overall abundance did not change. These were rapid changes, not gradual evolutionary shifts. The late-migrating fish practically disappeared within a few years. "It's sort of reassuring that organisms have the potential to adapt to the really major changes that are occurring," said the lead author, Ryan P. Kovach, a doctoral student at the University of Alaska, Fairbanks. But the fact that climate change is already forcing evolutionary changes should be raising red flags for resource managers and the general public alike.