Nutritional Overview of the Killer Whales (Orcinus orca)
Christian daSilva
My name is Christian daSilva and I'm a student at the University of Guelph. This website is my final project for the class ANSC 3180 - Wildlife Nutrition. My goal for this project is to educate my peers and the public on the unique nutritional traits of Killer whales.
The Killer Whale
Orcinus orca
Are they really as scary as they sound?
Killer whales, also called Orcas, are aquatic mammals within the order Cetartiodactyla in the cetacean clade along with whales, dolphins and porpoises. Orcas are the only species in the genus Orcinus and are the largest dolphins in the family Delphinidae. There are three ecotypes of killer whales (resident, transient and offshore) with distinct genetics, social behaviours and feeding specializations. (Ford, 2009; Reeves et al., 2017)
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The distinct colouration of orcas is unlike any other marine species. Their black dorsal side and white stomach help them camouflage in the dark ocean abyss and in the bright surface sunlight. They have white patches around their eyes and on the sides of their body. The 'saddle patch' is a grey-ish colour patch just posterior to their dorsal fin. The different ecotypes all have similar colouration, although southern populations are sometimes more grey than black. In newborn orcas, the white areas have a bit of yellow/orange hue but the white pigmentation quickly develops in the first year. (Ford, 2009)
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Killer whales are the marine apex predator for good reason. They are social hunters with the power and intelligence to take down even Great White Sharks. Newborn killer whales are born fully developed, around 2-2.5 m long and weighing nearly 200 kg following the 15-18 month pregnancy. Males will grow until physical maturity around 21 years old, reaching lengths of 9 m and weighing around 6600 kg. Females are smaller, reaching lengths around 7.7 m and weighing around 4700 kg. Females become sexually mature at 12-14 years old and become reproductively senescent around 40 years old. Male orcas can live up to 50-60 years, usually around 30, while females can live up to 80-90 years although usually around 50 years. (Ford, 2009)
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Image 1. The known range of extant killer whales (Orcinus orca) (Reeves et al., 2017)
Home Range
Killer whales are the most widespread mammalian species, second only to us humans. Their cosmopolitan distribution means they can be found in almost any ocean around the world. However, there are seasonal patterns of prey availability where many whales congregate in those regions during periods of prey abundance. In the fall, resident killer whales can be found along the shores of British Columbia and Washington, enjoying the Chinook salmon migration. Similarly, transient killer whales are most abundant during the pupping seasons of seals. (Ford, 2009; Ford and Ellis, 2013)
Conservation Status
Currently, the conservation status for killer whales is labelled as data deficient. The reasoning for this label is taxonomic uncertainty. Remember the three killer whale ecotypes mentioned above? The populations for each of these ecotypes are socially and reproductively isolated with quite different lifestyles, although are still considered a single species. The conservation of regional killer whale populations can be assessed, but it is challenging because these single populations can be under different stressors than the rest of the population. Taxonomic revision of Orcinus orca and its three ecotypes is necessary to confidently determine their conservation status. (Ford, 2009; Reeves et al., 2017)
Culture
/ˈkəlCHər/
The beliefs, behaviours and values of a group, passed on to further generations through through forms of social learning
Life History of The Killer Whale Ecotypes
Overview of the different behavioural and social cultures of the three killer whale ecotypes: residents, transients and offshores. All three ecotypes are thought to maintain these distinct features through forms of social learning, comparable to cultures that we humans are all too familiar with. The different dietary specializations of each ecotype will be covered in the diet and feeding.
Image 2. Example of variation between different populations of killer whales (Orcinus orca). (Ford, 2009)
Resident
Resident killer whales feed primarily on fish and teleost prey. The social structure of residents is extremely structured and stable. Matrilines are the primary social group, consisting of an older female (matriarch), her sons and daughters and their offspring as well. Matrilines can contain up to four generations of offspring and no cases have been reported where resident orcas leave their matriline to join another. You may have heard about pods of killer whales at Marine Land or Sea World. Pods are a group of matrilines with a common maternal ancestor. Pods usually contain around 3 matrilines but can have up to 11. The calls of killer whales are passed on through social learning within matrilines and pods. The final level of social organization for resident orcas is the clan. All the pods in a clan have similar dialects, unlike the other clans, likely a result of a common heritage. (Ford and Ellis, 2006; Ford, 2009; Ford and Ellis, 2013)
Transient
Transient killer whales primarily prey on endothermic and mammalian prey. The social structure of these orcas is not as strict as residents. Transients travel in smaller groups of about 2-6 individuals. The small group size is thought to help with stealth when hunting prey. Unlike residents, these killer whales have been seen to permanently leave their natal matriline. Juvenile females often travel with their mothers until they reach sexual maturity. At this point, females usually leave to other groups to start producing offspring. The male behaviours of transients are a bit more of a mystery. It is thought they hop from group to group, taking advantage of available food and mates, although individual males have been spotted. Transients do not have clan structures like residents because all transients in a population share distinct calls. (Ford, 2009; Ford and Ellis, 2013)
Offshore
Offshore killer whales are the least known of the three ecotypes. They have been seen further from shore than the other two ecotypes, as the name suggests. Offshores are thought to feed primarily on sharks and large fish. The social organization is not well understood, although they have been seen in groups of 2-100 individuals, larger than transient groups and comparable to resident pods. It is suggested that these large gatherings are composed of many smaller groups similar to residents, although this has not been confirmed. With the current information, offshores may disperse from their matrilines similar to transients, yet aggregate in large groups similar to residents. (Ford and Ellis, 2013)