By George Wykes
Meet the orcas
Orcas are the most widespread of all the whales and dolphins, inhabiting every ocean on the planet. Their trademark black and white colouration, incredible intelligence and incredible efficiency as an apex predator mean they have a place in many of our hearts. There is so much more to them than meets the eye, however as we will illustrate, there are numerous ecotypes of orcas that have their own special adaptations to hunting and prey preferences to go with it. It is theorised that this separation into different niches took place over millions of years of evolution to mitigate the risk of competing for the same food sources. These differences in ecotypes are not limited purely to food preference, they also extend to changes in appearance and behaviour and further highlight just how lucky we are to share the planet with these truly magnificent animals.
Northern hemisphere Orcas
North Atlantic Types 1 and 2.
Orcas in the North Atlantic are divided into two groups Type 1 and Type 2. Type 1 orcas are smaller and have a broader range to their diet taking advantage of migrating herring and mackerel but also have been recorded predating on seals too. Type 2 Orcas in correlation with their larger body size have larger prey preferences and focus mainly on marine mammals. These differences in diet are illustrated in the anatomy of their teeth. Type 2 Orcas teeth are bigger and sharper and therefore perfect for taking on mammalian prey whilst Type 1 Orcas teeth are predominantly worn as a consequence of a largely fish based diet.
These Orcas have earned their name as a result of small home ranges located in areas where prey fish populations are high. Intriguingly, Northern and Southern Residents have shown an almost exclusive preference for feeding on salmon while Residents in Alaska are less picky and take halibut, cod and many other species alongside salmon.
The social structure of Residents is also interesting, living in family groups which in turn belong to and make up populations of larger Orca communities. The motherly bond is strong between parent and baby and this continues as they stay together throughout their lives.
Bigg’s Orcas predate upon a variety of mammal species with preferences for prey items identified amongst different pods. They differ from Resident Orcas in having much larger home ranges, however the family bonds remain strong and it is not unusual for individuals to live in the same community for the entirety of their lifetime. Being top of the food chain unfortunately means these Orcas are at the highest risk of being affected by pollution consuming pollutants that have worked their way up the food chain and subsequently then become stored in their blubber with nowhere else to go.
Offshore Orcas are by far the most understudied of the Northern Orcas due to their elusive nature largely as a result of living considerable distances from land. It is known however that they can form social groups of over 50 strong individuals, have large home ranges and the worn nature of their teeth suggest a fish-based diet.
Orcas of the Southern hemisphere
The Orcas of the Southern hemisphere like those found in the North can be divided into different ecotypes and each have their own unique differences in behaviours and appearance that make them all incredibly unique.
Type A Orcas.
Type A Orcas are truly enormous , growing up to 31 feet in length and as a result of this take suitably large prey such as Minke whales by following their migration paths to and from the cold Antarctic waters.
Type B Orcas.
Type B Orcas are separated into two sub categories; large and small. The larger Orcas are also known as Pack Ice Orcas and are responsible for the seal washing behaviour documented on Frozen Planet. The smaller Orcas in contrast have less well known dietary preferences however observations have recorded them as predating on penguins.
Also known as the Ross Sea Orca, this is the smallest Orca ecotype of the Southern hemisphere with males reaching a maximum of 20 feet long. They are characterised by a very distinct slanted eye patch. While they have been known to feed on fish, it’s not known if their diet extends beyond this.
Tragically, the first time the Subantarctic Orcas came to the attention of the scientific community was during the 1950s following a mass stranding. It would be later that they were identified as their own species, or Orca, with the smallest eyepatches of all Orcas along with having a distinctively rounder head being the identifying traits that make it its own species. As with the Ross Sea Orca, the dietary preferences of this species are unclear, although Patagonian toothfish have been recorded as being predated upon in the past.
Did you know?
Orcas are not technically whales at all but instead are the largest member of the dolphin family.
Wolves of the sea
Orcas, otherwise known as killer whales are known as ‘the wolves of the sea’ and it could be strongly argued there is no better way to describe them. Their pack hunting behaviour is the biggest similarity between these animals and the reason for their nickname but it’s not the only trait they share. On land, wolves are capable of creating a landscape of fear as prey moves across areas of land and into new habitats in an attempt to make it harder for their pursuer to detect them. As a consequence, allowing for rejuvenation in previously grazed areas and allowing opportunities for other species to benefit in their absence. These changes in prey behaviour when not actively being hunted are described as nonconsumptive effects or NCEs. Orcas, likewise, strongly influence prey species behaviours just by having a presence in the area, thus creating a “seascape of fear”. Examples of this include forcing prey species such as narwhals and beluga whales to shorten their ranges and seek out the shoreline in attempt to avoid the Orcas predatory attentions. It has recently emerged that Bowhead whales too significantly change their behaviours in response to the presence of Orcas. Research found a dramatic difference in habitat usage from frequenting areas of open water to seeking out large areas of sea ice in the presence of Orcas during a three week tracking period. These changes in behaviour as a result of the presence of predators show not only fear an apex predator can induce as a result of its existence alone, but also the ability of prey species to adapt and attempt to counter predation attempts.
Photo ©George Wykes
It is well documented that humpback whales are sometimes seen as prey items for Orcas however recent research suggests that in some cases humpbacks can indeed benefit from the presence of Orcas. Over the course of three years between 2013 and 2016, scientists witnessed the feeding behaviour of Humpback and Killer whales that had gathered to feed on shoals of migratory herring in Andfjord, North Norway. What they found can only be described as remarkable. During the three years, the scientists completed 109 surveys. During these, Orcas engaged in feeding behaviour on 59 occasions. What is amazing is that in nearly 80 percent (79.7%) of these events, Humpbacks were also present and feeding. Not only this, but the data researchers suggest may show that Humpbacks are the higher beneficiary from this meeting of predators as in 94.4 of these feeding events it was the Orcas who seemingly opened the floodgates by first feeding on the herring shoals and in doing so presented the opportunity for the Humpbacks to make their move.
Did you know?
When Orcas dive they can go down as deep as 500ft!
Prey identification and seal washing by Pack Ice Orcas.
The incredible footage of seal washing behaviour by Pack Ice Orcas on the BBC’s Frozen Planet Series will live long in the memory of those who watched it. The waves created by the rushing Orcas had enough power behind them to knock seals clean off the ice flows breaking the flows in the process, hence the name “seal washing”. What is even more astonishing is the sheer ingenuity of these animals in their ability to clearly identify and specifically target seal species. Weddell seals, researchers found during a 2009 study, were predated upon fourteen out of the fifteen times seal kills were recorded. This despite the fact that Weddell seals made up just a small percentage of the total number of seals observed on ice flows. Not only this, but the success rate of these attacks has been recorded as being remarkably high too. It has been speculated that the preferences for Wedell seals over Crabeater and Leopard seals could be due to the more docile nature of Wedell seals.
Differences in acoustics when feeding at night in herring eating Orcas.
It has recently come to light that Orcas feeding on herring feed both at night and day, researchers in Iceland have discovered. They recorded Orcas as feeding during daylight 73% of the time, while feeding at night for 50% of their time. Interestingly, their findings also suggest that in low light conditions herding calls become more important than tail slaps, the behaviour otherwise known as carouseling. This is an important discovery and researchers suggest that this behavioural adaption is of particular benefit to predators operating in waters with limited light availability during winter.
Threats and how you can help.
One of the most malignant threats that face Orcas, particularly mammal eating ecotypes, are persistent bio-accumulating containments (PCBs). It is tragically ironic that their position at the top of the food chain which should lessen the risks they are exposed too, in fact heightens the chances of pollutants being stored in their blubber. As pollutants move through the food chain it is the apex predators in which they settle, an unnatural enemy threatening one of the greatest predators the planet has ever seen.
Noise pollution as a result of shipping vessels and other ocean traffic represent another threat to Orcas with the disruptions overpowering the echolocation signals Orcas depend on to communicate and locate prey. As a consequence, it opens the possibility to lower success rates when hunting and subsequently lower population numbers.
Like many cetaceans, these magnificent creatures have fallen foul of whaling which continues to happen in places such as Japan and Greenland. As well as direct hunting, Orcas also fall foul of bycatch through drift nets, longlines and trawling.
Appallingly, Orca are also infamously targeted for live entertainment shows. SeaWorld is one of the most high-profile examples of this and the heart-breaking documentary Blackfish documented the physical and emotional turmoil these animals have been subjected to. Southern Orcas have been historically targeted so much for these reasons, that their current populations are not even close to what they once were. Still this issue continues, with Orca still being subjected to capture for the purposes of entertainment in Pacific waters.
You can help change this, however, below is a link to sign a petition to stop not just Orcas but other cetaceans being forced to suffer from this kind of treatment. Animals that can swim for 40 miles a day and dive up to 500ft are about as suited for a life in captivity as a chocolate teapot is for boiling water.
There is no doubt that Orcas are one of the most diverse, adaptable and intelligent carnivores on the planet. What is equally clear is that our planet would be in a lot worse shape without them.
Meet the different types of orcas - Whale and Dolphin Conservation. (2019, July 23).
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