Orca

The orca is the apex predator of every ocean it lives in. Nothing hunts it. It is fast, enormous, intelligent, and — most importantly — it hunts in coordinated teams that pass their tactics down through generations.

Overview

Orcas are found from the equator to the polar pack ice, but they are most abundant in cold, fish-rich seas. Scientists increasingly think “orca” covers several distinct forms, or ecotypes, that look slightly different, eat different prey, sound different, and never interbreed even where they share the same water. The best-studied split is between fish-eating residents and mammal-hunting transients (also called Bigg’s orcas) in the North Pacific.

Physical characteristics

An orca is unmistakable: glossy black above, white below, with a white eye patch and a grey “saddle” behind the dorsal fin. That fin is a giveaway of sex and age — up to 1.8 m and near-vertical in an adult male, shorter and curved in females and youngsters.

Behind the smooth exterior is a 5–6 tonne animal that can hit 56 km/h, dive to several hundred metres, and hold its breath for 10–15 minutes. Its cone-shaped teeth interlock for gripping large, powerful prey.

Diet and hunting

Orcas eat almost anything in the sea, but each population specialises:

• Fish specialists herd salmon or use “carousel feeding” — circling a school of herring, blowing bubbles and flashing their white undersides to pack the fish into a ball, then stunning them with tail slaps.
• Mammal hunters take seals, sea lions, dolphins, and whales. In Antarctica, pods swim in formation to create a wave that washes a seal off an ice floe. Off Argentina, they deliberately beach themselves at speed to snatch sea lion pups from the shore, then wriggle back into the surf.
• Some populations hunt sharks, flipping them upside down to induce paralysis and removing the liver.
• A few pods coordinate to separate and drown large whale calves, and there are records of orcas killing blue whales.

Society

Orca society is built on the matriline — a mother and all her descendants. In resident populations, neither sons nor daughters ever leave their mother’s group; pods are stable for decades. Related matrilines form pods, and pods that share calls form clans.

Females go through menopause, one of only a handful of animals known to do so, and post-reproductive grandmothers act as knowledge-keepers, leading the pod to food in lean years. Each clan has its own vocal dialect, learned not inherited.

Reproduction and life cycle

Females give birth to a single calf every three to ten years after a 15–18 month pregnancy — the longest of any dolphin. Calves nurse for up to two years and are cared for by the whole matriline. First-year calf mortality is high, around 40%, and females typically stop reproducing in their forties while living into their eighties or beyond.

Threats and conservation

Because “orca” may be several species, the group is listed as Data Deficient. Some populations are stable or growing; others are in freefall:

• The Southern Residents (US/Canada Pacific coast) are down to about 75 whales. They depend on Chinook salmon, which have crashed, and they carry among the highest levels of banned industrial chemicals (PCBs) of any animal, which impair reproduction and immunity.
• Noise pollution from shipping and whale-watching boats interferes with the echolocation orcas use to hunt.
• The live-capture era of the 1960s–70s removed dozens of young orcas from Pacific Northwest pods for marine parks, a gap those populations have never recovered from.