In our blogs we have chatted about all the different parts of what we do and see, talking about the food network of phytoplankton, krill, penguins and seals. The top of the food chain, though, is the killer whale, which has no natural predators.
The killer whale is also known as the orca whale or blackfish. These whales are found in oceans from the Arctic to the Antarctic and warm tropical oceans between.
My current assignment is to go to the edge of the ice, where the killer and minke whales hang out, and help tag and photograph these huge, gorgeous mammals. As a mammal, they give birth to live calves who feed on the mothers milk, need air to breath, are warm blooded, and have a form of communication, among other traits.
Why are we studying all the layers of the ecosystem and food web here? By looking at the interactions of all the dominant predators (penguins, Weddell seals, and Ross Sea killer whales), we can look at the interactions that exert pressure on the prey (krill, silver fish, and other small fish) and the distribution of the prey.
To some, killer whales look exactly alike, however, they can be distinguished from one another by the shape and size of their dorsal fins, the distinctive grayish-white saddle patches behind their dorsal fins, as well as distinctive scars, nicks and marks on their dorsal fins. Photographic identification has enabled the local population of killer whales to be counted each year rather than estimated, and has enabled great insight into lifecycles and social structures.
Although they may look similar, there are 4 types of killer whales:
- Type A looks like a ‘typical’ killer whale with a medium sized white eye patch and feeds mostly on minke whales.
- Type B is smaller than Type A, has a large white eye patch, and feeds mostly on seals and penguins.
- Type C is the smallest and lives in larger groups than the others. Its eye patch is slanted forwards, and preys on small fish and Antarctic cod. This one is common in the Ross Sea area, and is the main one we are studying.
- Type D has a much smaller white eye patch, smaller teeth and shorter dorsal fin. And nobody knows what they like to eat!
Types B and C live close to the ice pack and the diatoms (a type of algae) in the water may be responsible for the yellowish coloring on the white or grey parts of their bodies for both types.
Males typically range from 20 to 26 feet long and weigh in excess of 6 tons. That’s as long as 2 cars parked end-to-end, but about as heavy as 3 cars! Females are smaller, generally ranging from 16 to 23 feet and weighing about 3 to 4 tons. Calves at birth weigh about 400 pounds and are about 8 feet long. That’s a baby roughly the size of a tiger. The killer whale’s large size and strength make it among the fastest marine mammals, able to reach speeds in excess of 35 miles per hour, which is pretty darned fast swimming.
Killer whales have good eyesight above and below the water, excellent hearing, and a good sense of touch. They have exceptionally sophisticated echolocation abilities, detecting the location and characteristics of prey and other objects in their environments by emitting clicks and listening for echoes.
The mean body temperature of the orca is 97 to 100°F. Like most marine mammals, orcas have a layer of insulating blubber ranging from 3 to 4 inches thick beneath its skin.
The heart beats at a rate of about 60 beats/min when the orca is at the surface, dropping to 30 beats/min when submerged.
Gestation varies from 15 to 18 months, meaning a female whale could be pregnant for a year and a half! The lifespans of wild females average 50 years, with a maximum of 80–90 years. Wild males live around 29 years on average, with a maximum of 50–60 years. Captive killer whale lifespans are typically significantly shorter, usually less than 25 years. Killer whales are social animals that live in stable family-related groups.
Some local populations are considered threatened or endangered due to prey depletion, habitat loss, pollution, capture for marine mammal parks, and conflicts with fisheries.
It is reported that wild killer whales have never killed a human being and are not considered a threat to humans. However, there have been cases of captive orcas killing or injuring their handlers at marine theme parks; it is theorized that the captive whales felt threatened by their trainer.
Day-to-day killer whale behavior generally consists of foraging, travelling, resting and socializing. Spyhopping, a behavior in which a whale holds its head above water, helps the animal view its surroundings.
With developed fishing, from many countries, for Antarctic fish and whales, the tightly coupled system of this food web in Antarctica could be damaged. We need to be aware that reducing or removing any of this food chain could affect all the other animals in the system, and learning how it all fits together lets us make informed choices.