Only around 80 orcas are living in Puget Sound, threatened by pollution and a limited food supply, according to a new study from the National Oceanic and Atmospheric Administration.
The report, which is based on a data collected by scientists over the last decade, revealed that the Puget Sound orcas are among the marine mammals most affected by pollutants, the Associated Press reported.
The three biggest threats to the killer whale population are decreasing numbers of prey, noise from vessels passing through and pollution. Learning from the new report's findings, researchers now know which fish orcas prefer to eat and how they interact with one another as well as why their population has fallen.
"We've made some significant progress in understanding each of the three primary factors of decline," said Mike Ford, director of the Conservation Biology Program at the Northwest Fisheries Science Center, as quoted by the AP.
For the NOAA report, scientists tracked orcas with acoustic monitoring and satellite tags, following their movements during winter migration. They found that their summer diet is mostly composed of Chinook salmon from the Fraser River in British Columbia.
The animals also eat halibut and tend to hunt less and call more loudly when boats are nearby. The Puget Sound orca population, which travels as far south as Central California to eat salmon from the Columbia and Sacramento rivers, was found to contain high levels of banned pollutants including PCB.
The southern resident killer whale population has declined from more than 140 decades ago, falling to 71 in the 1970s and coming in at 82 in 2013. The lowest population point stemmed from the practice of capturing live orcas to be displayed in marine parks and aquariums.
Orcas have been listed as endangered since 2005, with efforts to conserve the species starting in the 2000s.