Introduction To Orcas (Killer Whales)
|Adult orca with juvenille|
Orcas (Orcinus orca), commonly referred to as “killer whales” and “wolves of the sea,” are noted for their pack-like hunting techniques that demonstrate intelligence and cunning with spectacular displays. They are a locally common sight in the Southern Ocean and often spotted during our cruises. Globally they have been known to feed on seals, fishes, squid, seabirds (including penguins) and other whale species, making the coastal zone of Antarctica a prime hunting ground. But, just as elsewhere, foraging specialization among groups is not uncommon.
Identifying Orcas—Physical Characteristics
Known as Orcinus orca in scientific literature and sometimes called simply orca, the largest members of the dolphin family are immediately distinguishable by their black and white pattern and by their size. Worldwide, males attain maximum lengths up to 30 feet and weights of six tons, and the females reach up to 26 feet in length and slightly more than four tons in weight—but with increasing information about the Antarctic groups, these figures vary. One of the most obvious characteristics that aids in the determination of whether or not one is seeing a male or a female is the shape of the dorsal fin, a field mark easily discernible from a ship. Male dorsals can be up to six feet long, one-fifth of their overall length, and are tall and erect. Female and juvenile dorsals tend to be falcate (curved back) and usually do not exceed three feet. The underside of the tail fluke is white. Characteristics used to identify individuals include variations of the dorsal fin, the eyepatch—a white spot of varying shape and orientation behind their eye, and the presence and/or shape of a dorsal cape. They have a fine, bushy, conspicuous blow that frequently signals their presence.
|Orcas near Deception Island, Antarctica|
Exciting to watch, orcas have a behavioral repertoire seemingly made for shipboard viewing. Breaching—involving graceful leaps completely out of the water with thrilling re-entries, tail-slapping, spy-hopping and logging—whereby the entire group faces in the same direction in close proximity to each other—offer numerous opportunities to observe these striking animals in their environment.
Southern Ocean Types—Distribution, Migration and Descriptions
Orcas are considered the most cosmopolitan of the toothed whales. From the Arctic Ocean to the Gulf of Mexico to the Southern Ocean, whale watchers and mariners are fascinated with these impressive giants cruising in groups from a half dozen to a couple of hundred strong that easily move between hemispheres. Whereas observations of Pacific Northwest populations are well publicized and have been on going for decades, suspicion that there are different groups in Antarctica began with analysis of catch data from the Soviet whaling fleet in the late 1970s. Building from there, and with a review of photographic evidence and research reports, three types of “field-identifiable forms” of killer whales—differing in distribution, prey, hunting technique or color pattern—have been described in Antarctica.
Type A orcas are described as the typical form that forages in ice-free areas, generally well offshore, and feeds on marine mammals, primarily Antarctic minke whales. They have a distinct black and white patterning, a medium-sized eyepatch that is oriented along the same line as the body axis, and they are for the most part circumpolar in distribution. The largest of the Antarctic types, they can be as large as the maximum sizes described for the species. Although there is not a lot known specifically about these animals, it is believed that they leave Antarctica in the austral autumn to follow the migrating Antarctic minkes to the lower latitudes.
|Type B orca in Antarctica|
Type B and Type C have been found to be pagophilic, or ice-loving. Both have been described as being up to a meter and a half smaller than the C form, with adult male dorsals of the B form being described as relatively smaller as well. Diatoms that give them a yellowish tinge frequently grow on the surface of their skin, considerably lightening their coloration to brown or gray rather than black. A distinctive dorsal cape of lighter shading behind their dorsal fin is characteristic of both types.
Type B have an eyepatch that is oriented parallel to the body axis, but the patch is much larger than the eyepatch of Type A. Although there are exceptions, these animals prey most often on seals and tend to stay close to the loose pack ice which is sighted regularly in the Antarctic Peninsula area. It is this type that provides spectacular viewing as they create massive pressure waves with their muscular flukes to rock small ice floes used by hauled out seals—dramatically rolling the seals into the water where the rest of the group waits to feed. It is not clear whether this type is a year-round resident, particularly since most records and photographs are taken during the summer, but as their prey tends to say put, it would not be unexpected. There have been sightings of Type B orcas both in the Falkland Islands and in the Bay of Islands in New Zealand, during the winter months as well as around the Antarctic pack ice.
|A pair of orcas surfacing|
The third group, Type C, is generally found off East Antarctica and the Ross Sea. Its presence is often documented in the dense pack ice, along leads in the fast ice and in polynyas (open areas in the pack ice). Morphologically this diminutive type differs by having a small forward slanting eyepatch. The only records of its feeding preferences name the Antarctic toothfish as its primary prey.
The most recent scientific work, based on molecular analysis, has centered on determining whether the three types are separate species. If standard coloration categories were used for all other killer whales outside of Antarctica, they would be considered Type A, so it is not surprising that Type A, the offshore group, did show a strong pattern for genetic isolation from the other two. Types B and C are closely related genetically and it may be that the preferential use of the sea ice habitats has had a major effect on this divergence.
Orca Breeding and Population
Only the most basic information is available on killer whale breeding, and most of that has been collected from captive animals. It is believed that they become sexually mature between the ages of 10 and 18 years of age and actively reproduce when the males are about 20 feet in length and the females about 16 feet in length—but keep in mind that may vary with the “dwarf” Types A and B in Antarctica. Females breed until they are 40 years of age and have a life span estimated to be 80 to 90 years. It is unknown how long males continue to breed, but their life span is considerably shorter at 50 to 60 years of age. The gestation period is 15–18 months and, when born, the young are typically 7 to 8.5 feet long and weigh around 350 pounds.
|Orca blowhole clearly visible|
Global population estimates are difficult to compile, although some have speculated that there are 80,000 killer whales in Antarctic waters in the austral summer.