The largest of the dolphin family, growing up to 10 metres long, and weighing as much as 10,000 kilograms, orcas are found in all the world’s oceans, but mostly in the colder waters of Antarctica, the North Atlantic and the Pacific.
These charismatic cetaceans can dive for more than 10 minutes at a time, conserving oxygen by slowing their heartbeats from 120 to 30 beats a minute. They communicate using clicks, squeaks and whistles, like other dolphins, and each pod has their own dialect. Orcas have also been discovered to be able to learn other languages, speaking “dolphin” when kept captive with them.
With the second largest brain of all marine mammals, orcas are complex, social creatures, living in pods with established, matriarchal social hierarchies. Fast, orcas can swim up to almost 50 kilometres per hour to catch prey, of which they eat about three to four percent of their body weight, around 100 kilograms, each day. They hunt like wolves, in packs, working together to encircle and herd prey into a small area before attacking. They have also been known to intentionally beach themselves when hunting sea lions and pups in coastal areas.
The Red List classifies orcas as a Data Deficient group, but the reality is that some specific populations are already threatened.
In the Pacific Northwest, along the Washington, British Columbian and Alaskan coasts, orcas fall into two distinct groups: transient and resident. Physically, the two are very similar but there are some differences.
The top of the dorsal fin of transient orcas tends to be more pointed than that of residents. Less obvious, the saddle patch is further forward in transients. Resident whales prefer a diet of fish, and in the summer months almost exclusively salmon. Transients, however, prefer to eat marine mammals.
A lot of the time transients travel around silently in small groups. This perhaps enables them to listen intently, lessen their presence in the water, and sneak up on their prey. This is in contrast to the resident pod, which tends to be more vocal, sociable and live in extended family groups.
This article featured in SD OCEAN PLANET (Issue 2/2015)