When studies of the orcas of the Pacific Northwest began in the 1970s, fish-eating orca pods were labeled “resident”, as they were seen regularly from April to September. On occasion, other smaller pods of orcas would come into the same waters, but due to the lack of regular sightings they became known as “transient”; these were not salmon specialists, instead targeting seals and sea lions.
Prior to these studies, the total number of orcas in the Pacific Northwest was unknown and overestimated. There was an assumption that orcas were plentiful, when in fact it was the same pods seen regularly. This work to document the small populations of Northern and Southern Resident orca communities led to a ban against capturing any orcas from these waters for captivity.
In recent years, with the continuing decline of Chinook salmon, the so-called resident orcas are spending less time in their traditional fishing grounds while they seek salmon in open coastal waters. Transients, whose food is abundant, are spending more time in the Salish Sea. If research started on these orcas today, it’s possible the transients could be labeled resident.
While these labels have stuck (though unique to the Pacific Northwest orcas), orca biologists prefer to reference differences between populations as “eco-types” which is usually a combination of their prey choices, range and habitat.