What is an orca? The orca is a toothed whale and one of close to forty species in the ocean dolphin family, and its fossil history goes back to the Pliocene epoch, about 5 million years ago, although the record is not rich. Up to 23 species and four subspecies of killer whales were named in the literature, many from the skull of a single specimen, and these were later merged into one species. In 2004 a workshop of scientists judged that there were probably several subspecies or species of killer whales, but that the data were not yet enough to change the name. Most recently, in 2024, researchers wrote that Bigg's and resident orcas in the eastern North Pacific should be recognized as two separate species.
Ecotypes vary in body size, color pattern, social structure, vocalization and foraging strategy, and scientists think Bigg's and resident orcas may not have interbred for hundreds of thousands of years. Researchers have identified three main types of orcas in Antarctic waters and a fourth in the sub-Antarctic. In 2019, scientists off southern Chile spotted a kind of orca with small eyepatches and blunter heads, called Type D, that may be a new species. Orcas have been counted for only a few decades, since the 1970s, so researchers are not sure how many are in each ecotype. Scientists estimate there are around 50,000 orcas in the world, as of November 2026, and about 25,000 to 27,000 of them live around Antarctica, as of November 2026, in the largest group of all.
Sound is one way to sort the groups: in 2022 Scripps scientists showed that echolocation clicks can tell the three ecotypes apart, using recorders called HARPs that sat on the seafloor at depths of 120 to 1,400 meters for about a year at a time. Whistles take years of training to tell apart by ear, so scientists hope clicks can help computers sort decades of recordings. The method has a limitation, however, because the Scripps team found that transient orcas' echolocation clicks were the hardest to detect, and an expert said that they can bury the clicks in background sound. Bigg's orcas stalk their meals in silence, probably because their prey use sound too.
For the Southern Residents, the question is less about names than about numbers. Scientists estimate they once numbered at least about 140 animals, and the population reached a peak of 98 whales in 1995, then fell by almost 20 percent in the late 1990s, leaving 80 whales in 2001. The Center for Whale Research has counted them by photo ID every year since 1976, and the count was 76 on July 1, 2026, up from 74 in 2025. NOAA's delisting goal needs a population growth rate of 2.3 percent over 28 years; the whales grew in 2025 and 2026, but past growth has been followed by longer declines, as of July 2026. The Center for Whale Research says survival rates are closely tied to Chinook salmon abundance, as of July 2025. An Antarctic orca researcher says that whales who spend 50, 60 or 80 years with their family can hunt cooperatively and pass on what they learn.
Words to know
- subspecies: sub-kind
- specimen: one sample
- foraging: searching for food
- delisting: removal from list
- Pliocene: ancient epoch
