Rising ocean temperatures are thought to be a factor in the large scale movement of fish stocks. Using actual temperatures of harvested fish, scientists have now tracked the shift of warm weather species towards the poles.
Because fish are cold blooded, they are totally dependent on surrounding temperatures to stay alive. And as they’re highly mobile, fish species will move to where the temperatures are most comfortable. That’s the idea behind a study led by scientists from the University of British Colombia.
Dr. William Chueng and the team began by assigning 968 species of fish a preferred temperature range. Sockeye Salmon are at home in water from 3 to 6 degrees Celsius. Pacific Hake are happiest at 13 degrees Celsius.
Researchers then dug into a vast trove of fish temperature data reported by the fishing fleet going back 40 years. The team crunched those numbers through a complex algorithm to find the average fish temperature in a given geographic area.
"If there are increasing representations of warmer water species, say in Alaska, we would expect to see that the mean temperature of the catch would increase because of the increasing representation of species that prefer a higher temperature," said Cheung.
Across the globe, temperatures jumped two tenths of a degrees Celsius per decade. Researchers worked on extremely broad scale and didn’t note specifically which warm water species might be moving into northern waters. Cheung did note that some southern populations of salmon have struggled in recent years while other salmon stocks in the north have done better.
Looking to the decades ahead, climate projection models expect that oceans will continue to warm.
"It means that we will see more and more warmer water species in the fisheries' catch in the northern areas," said Cheung.
The study was funded by the National Geographic Society and Pew Charitable Trusts’ “Sea Around Us” project. It was published in the May issue of the scientific journal Nature.