Pink Salmon

(PBMW/Corbis)

Environmental factors often drive migratory behavior patterns in animals. For salmon, migration is crucial to their survival as a species, because the fish swim from the ocean and up freshwater streams to spawn. The need to migrate is so strong it is even written into their genes. In Auke Creek, Alaska, one pink salmon (Oncorhynchus gorbuscha) population is migrating about two weeks earlier than it was 40 years ago. So scientists looked at both genetic and migratory data over 32 years to see if genetic changes were behind the switch.

The team found that between 1983 and 2011, the frequency of a genetic marker for late migration dropped significantly. By 2011, late migrating fish only made up about 10 percent of the population. Over that same time period, the local water temperature has increased by about one degree Celsius on average, an uptick that’s linked to climate change. The researchers argue that earlier migrating fish are better fit to handle warmer waters. Auke Creek salmon populations have held steady over the last few decades, and this adaptation may have made them more resilient.