Total Numbers and Movements of Photo‐Identified Subantarctic (Type D) Killer Whales

ABSTRACT The distinctive Subantarctic (Type D) killer whale (DKW) ( Orcinus orca ) is a highly divergent and apparently inbred form previously known only from three mass strandings and several dozen at‐sea sightings, primarily from Patagonian toothfish ( Dissostichus eleginoides ) longline vessels in the southern Indian Ocean and from tourism vessels in the Scotia Sea. Its range appears to be circumpolar throughout the Subantarctic, but very little is known about total numbers and overall movements. We summarize photo‐identification data from 352 of 406 sightings collected between 44° S and 62° S from 2003 to 2024. Among 207 photo‐identified individuals there were two distinct clusters of 78 and 29 toothfish depredators, one in the southern Indian Ocean and the other off southern Chile, respectively. An additional 100 DKW were photo‐identified throughout the wider Subantarctic. Discovery curves indicate that DKW may be more abundant than some less divergent or inbred killer whale populations. Depredating DKW showed seasonal and interannual site fidelity, but 10 depredating individuals identified in the southern Indian Ocean were also resighted in the southern South Atlantic, 4428 km away. Probable re‐sightings of two other DKW occurred in the Scotia Sea over distances of 1070 and 41 km, respectively. These latitudinally narrow, long‐distance inter‐ocean movements are unique among killer whales. During the study period, the entirely pelagic distribution of encounters appears to have shifted significantly southward.