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Killer whale is not a whale???

Orcas, or killer whales, are the largest of the dolphins, belong to the Oceanic dolphin family and one of the world’s most powerful predators. They’re immediately recognizable by their distinctive black-and-white coloring. Smart and social, orcas make a wide variety of communicative sounds, and each pod has distinctive noises that its members will recognize even at a distance. They use echolocation to communicate and hunt, making sounds that travel underwater until they encounter objects, then bounce back, revealing their location, size, and shape. Photo: Kenneth Balcomb/Center for Whale Research

Foods

Orcas are apex predators, at the top of the food chain. No other animals (except for humans) hunt orcas. Killer whales feed on sea birds, squid, octopuses, sea turtles, sharks, rays and fish. They also eat most marine mammals, such as seals and dugongs. The only exceptions are river dolphins and manatees, according to the IUCN. Killer whales have also been reported to eat moose, according to Sea World. Killer whale and Weddell seal. Killer whale and Weddell seal. Orcas use many different techniques to catch prey. Sometimes they beach themselves to catch seals on land, meaning they jump from the water onto land. Orcas will also work together to catch larger prey or groups of prey such as schools of fish. Killer whales also work together to take care of the young in a pod. Often, young females will help the mothers care for young orcas

Hunting behaviors

Photo: Cao Minh Chau/Wildhand

Orcas hunt in deadly pods, family groups of up to 40 individuals. Killer whales hunt varied prey including fish, cephalopods, mammals, sea birds, and sea turtles and event the great white sharks. By hunting with the pod (usually a family of 3-5 individuals or even two families together), they separate the whale calf from the mother and constantly use the head blows, terrify to attack the whale until the whale dies. Orca is equipped with 50 sharp teeth, however, they are not enough to bite the fat and thick skin of the whale calf. Hence, they eat the most vulnerable part of the whale, which is a protein-rich tongue. And the great white shark also suffered a similar result. During the hunt, the female are the ones in the middle of the siege and do a harder job than the rest because the male has longer and sharper fins to surround their preys.There appear to be both resident and transient pod populations of orcas. These different groups may prey on different animals and use different techniques to catch them. Resident pods tend to prefer fish, while transient pods target marine mammals. All pods use effective, cooperative hunting techniques that some liken to the behavior of wolf packs.

Reproduction

Photo: Pixabay

Orcas are protective of their young, and other adolescent females often assist the mother in caring for them. Mothers give birth every three to ten years, after a 17-month pregnancy. They give birth to one baby at a time, which may nurse for up to two years. In most cases, the bond between juvenile and mother will eventually weaken, and the young orca will go its own way, but in some pods, the juvenile may stay with the pod it was born into its entire life. Almost half of all the babies die within their first year. Females only breed for about 25 years then they stop when they are about 40 years old. Thus, each female only produces about 4-6 surviving offspring in her life.

Killer whales in captivity

Photo: skeeze/Pixabay

Orcas are highly intelligent, social mammals that have long been a part of marine park entertainment, performing shows for audiences. However, it’s become increasingly clear that orcas do not thrive in captivity. They have evolved to swim up to 40 miles a day, foraging for food and exercising. They dive 100 to 500 feet, several times a day, every day. Whether they’re born in the wild or in captivity, all orcas born have the same innate drive to swim far and dive deep. Artificial enclosures in captivity cannon offer that kind of range to orcas, contributing to boredom and stress. Orcas have been seen to develop stereotypies, also known as zoochosis—repetitive patterns of activity that have no obvious function, which range from self-mutilation to rocking and swaying. Usually related to stress and inappropriate habitats, stereotypic behavior has been documented in orcas in scientific research since the late 1980s. In the wild, orcas live in tight-knit family groups that share a sophisticated, unique culture that is passed down through generations, research has shown. In captivity, orcas are kept in artificial social groups. Captive-born orcas are often transferred between facilities, breaking up social relationships. The stress of social disruption is compounded by the fact that orcas in captivity don’t have the ability to escape conflict with other orcas, or to engage in natural swimming behaviors in pools. More information can be found here.

In 2013, the documentary film Blackfish laid bare the psychological toll of captivity, through the story of a wild-caught orca named Tilikum who had killed two trainers at SeaWorld Orlando. The film included testimony from former SeaWorld trainers and cetacean specialists, who argued that Tilikum’s stress directly led to his aggression towards humans. Link to the film.

Threats

Photo: Skjervøy
  1. Hunting: Killer Whales have been hunted in several regions. Norwegian whalers in the eastern North Atlantic took an average of 56 whales per year from 1938 to 1981. Whalers in Japan took an average of 43 per year in coastal waters from 1946 to 1981. Soviet commercial whalers took an average of 26 Killer Whales annually from 1935 to 1979, primarily in the Antarctic, and then took 916 animals in the 1979/80 Antarctic season. Killer whales are also taken in small numbers for food (or as a population control measure) in coastal fisheries in Japan, Greenland, Indonesia, and the Caribbean islands.
  2. Tourism: Whales are subject to whale-watching tourism. Moving boats can disrupt foraging and resting, and underwater boat noise can affect social and echolocation signals of the whales or otherwise interfere with foraging. For example, close approaches by whale-watching vessels have been shown to result in avoidance responses by resident Killer Whales in British Columbia, which presumably has energetic costs to whales that are frequently subjected to this activity. Fast-moving boats in the proximity of Killer Whales also present a risk of vessel strikes.
  3. Pollution: Persistent bio-accumulating contaminants present a serious potential risk to some Killer Whale populations. Scientists reported that total polychlorinated biphenyl (PCB) concentrations were very high in three Killer Whale populations (2 resident and 1 transient) frequenting the coastal waters of British Columbia, Canada. Transient Killer Whales were particularly contaminated due to their high trophic position in the marine ecosystem. PCB levels in most Killer Whales sampled were greater than levels established at which adverse effects occur in Harbor Seals, suggesting that the majority of free-ranging Killer Whales in this region are at risk of toxic effects. The southern resident and transient Killer Whales of British Columbia and Washington are considered among the most PCB-contaminated cetaceans in the world. More recently, Paul Jepson at the Zoological Society of London found very high mean blubber PCB concentrations in Killer Whales in Europe. Small or declining populations of Killer Whales in the northeastern Atlantic (e.g., the very small population associated with the Strait of Gibraltar) have been associated with low recruitment, which is consistent with PCB-induced reproductive toxicity. Also, increasing levels of polybrominated diphenyl ethers which, like PCBs, can cause immunotoxicity, neurotoxicity, and reproductive impairment, have become a concern in the southern resident population in British Columbia and Washington. The Exxon Valdez oil spill in Alaska in March 1989 was strongly correlated with the subsequent loss of Killer Whales from transient and resident pods that had been seen swimming near or through oil slicks early in the spill. The AT1 pod had at least 22 individuals when first censused in 1984, before the spill. Eleven individuals have been missing from this pod since 1990 and two more since 1992. Four more whales from this pod died in the early 2000s and there have been no recorded births within the pod since 1984. As of 2012, only 7 of the original 22 AT1 pod members remained.

References:

  1. https://ptmsc.org/programs/investigate/citizen-science/completed-projects/orca-project/resident-and-transient-orcas
  2. https://www.iucnredlist.org/species/15421/50368125
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4997274/
  4. https://www.nationalgeographic.com/animals/mammals/o/orca/
  5. https://vi.wikipedia.org/wiki/C%C3%A1_voi_s%C3%A1t_th%E1%BB%A7
  6. https://www.livescience.com/27431-orcas-killer-whales.html
  7. https://www.marinebio.net/marinescience/05nekton/KWreproduction.htm
  8. https://www.nhm.ac.uk/discover/quick-questions/what-do-killer-whales-eat.html

 

Cao Minh Chau, August 22th 2019

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