A lack of chinook has been blamed for the southern residents’ declining population and low birth rates. The orcas rely almost exclusively on chinook as a food source. Only 73 of them remain, in three pods.
The increasing northern resident population numbers about 300. In recent years, southern residents have also been returning later than normal to the inside coastal waters of British Columbia and Washington. Researchers spent the summers of 2018 and 2019 surveying two areas known to be important foraging habitats for resident orcas — the Johnstone Strait for northern residents and the Juan de Fuca Strait for southern residents, where the orcas intercept migrating chinook returning to the Salish Sea.
The study, however, did not assess other factors that might prevent the orcas from catching the fish, such as higher vessel presence and noise in the Juan de Fuca Strait compared with Johnstone Strait.Article contentSato said the focus of ongoing research on the southern residents’ health should be directed to prey availability in other areas where the residents forage, and in different seasons.