World Orca Day is celebrated annually on July 14. The aim is to raise awareness of Orca and the threats they face, thereby increasing the protection of Orca and oceans.

Orcas are the top predators in the ocean, and these iconic animals are also known as keystone species. This means that they play a vital role in marine ecosystems. Orca is a species that can tell us about the health and well-being of an ecosystem, so it is also called an indicator species.

Orca, also known as the killer whale, is the largest member of the Delphinidae family or dolphins. The scientific name of the orca is Orcinus orca. They are found in every ocean in the world, and they are the most widely distributed of all cetaceans (whales and dolphins). While they are most abundant in colder waters like Antarctica, Norway, and Alaska, they are also found in tropical and subtropical waters. It is estimated that there are around 50,000 killer whales globally. Approximately 2,500 killer whales live in the eastern North Pacific Ocean, which is home to the most well-studied killer whale populations. Scientific studies have revealed many different populations with distinct ecotypes of killer whales worldwide, some of which may be different species or subspecies. They are one of the most recognizable marine mammals with their distinctive black and white bodies. Adult males develop disproportionately larger pectoral flippers, dorsal fins, tail flukes, and girths than females. Killer whales are highly social, and most live in social groups called pods. Pods typically consist of a few to 20 or more animals, and larger groups are sometimes formed for temporary social interactions, mating, or seasonal concentrations of prey. Killer whales rely on underwater sound to feed, communicate, and navigate. Pod members communicate with each other through clicks, whistles, and pulsed calls.

Orca whales are unlikely to attack humans out of aggression or hostility because of their intelligence and social nature. In fact, there have been numerous instances of orca whales coming to the aid of humans who were in danger, such as when a group of orca whales helped a diver escape from a shark attack.

Although the diet of killer whales depends to some extent on what is available where they live, it is primarily determined by the culture (i.e., learned hunting tactics) of each ecotype. For example, one ecotype of killer whales in the U.S. Pacific Northwest (called Residents) exclusively eats fish, mainly salmon, and another ecotype in the same area (Transients or Bigg’s killer whales) primarily eats marine mammals and squids. Killer whales often use a coordinated hunting strategy and work as a team to catch prey. They are considered apex predators, eating at the top of the food web.

The average lifespan for male killer whales is about 30 years, but they can live up to at least 60 years. Females typically live about 50 years but they can live up to at least 90 years in the wild. Females reach sexual maturity when they are between 10 and 13 years old. They are typically pregnant for 15 to 18 months and give birth to a single calf. Calves nurse exclusively for at least a year, but remain in close association with their mother for the first two years. There is no distinct calving season, so birth can take place in any month. Killer whales, beluga whales, narwhals, short-finned pilot whales, and humans are the only known species that go through menopause.

Threats to Orcas

1) Entanglement

Killer whales are at high risk of becoming entangled in fishing gear. Once entangled, whales may drag and swim with attached gear for long distances or be anchored in place and unable to swim. Events such as these result in fatigue, compromised feeding ability, or severe injury, which may ultimately lead to death.

2) Lack of food

Overfishing and habitat loss have decreased the amount of prey available to some killer whales. Without enough prey, killer whales might experience decreased reproductive rates and increased mortality rates. This threat is especially important for Southern Resident killer whales because some populations of their preferred prey, Chinook Salmon, are also threatened or endangered.

3) Contaminants

Contaminants enter ocean waters and sediments from many sources, such as wastewater treatment plants, sewer outfalls, and pesticide applications. Once in the environment, these substances move up the food web and accumulate in top predators, such as killer whales, because of their long lifespan, position at the top of the food chain, and blubber stores. These contaminants can harm killer whales’ immune and reproductive systems.

4) Oil spills

The 1989 Exxon Valdez oil spill in Prince William Sound, Alaska, was strongly correlated with the direct loss of individual killer whales. However, oil spills can also have an indirect impact on killer whales by affecting the abundance of prey species. In addition, the bioaccumulation of certain contaminants, like those found in oil, such as polychlorinated biphenyls (PCBs), in the food web can be seen in apex predators like killer whales and particularly among the transient population.

5) Disturbance from vessels and sound

When vessels are present, killer whales hunt less and travel more. Noise interference from vessels, as well as from industrial and military activities, interrupts killer whales’ ability to use sound, which in turn disturbs their feeding, communication, and orientation. Hunters and fishermen once targeted killer whales. As a result, historical threats to killer whales included commercial hunting and culling to protect fisheries from killer whales. In addition, the live capture of killer whales for aquarium displays and marine parks is a global threat.

Efforts to establish critical habitat, set protective regulations, and restore prey stocks are essential to the conservation of Orcas, especially for the endangered Southern Resident Killer Whale population.

Written by:

Sandini Gihansa

1st Year Undergraduate

Biological Science

Faculty of Science

University of Colombo.

References:

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