As the most widely distributed cetacean in the world, it’s understandable that orcas (also known as killer whales) might have altered their behaviour to suit the environment they live in. Much like on land, underwater habitats can vary greatly depending on their location: water temperature, plant life, prey availability, and topography all come into play, and the orca must adapt accordingly. You may have heard that some orcas eat mammals, while others eat fish, and that some in South Africa even go after great white sharks. You might also know that orcas in Antarctica hunt seals by breaking up the ice floes they rest on, while those in Scotland hunt seals by trapping them in rocky coves. But did you know that orcas have taken this one step further?
In the process of evolution, animals adapt to their ecology (which includes their environment, diet, social behaviour, and other species in the area) by undergoing a series of tiny changes that eventually build up to a different attribute. This allows them to perfectly suit their own ecology, otherwise known as their ecological niche. Orcas are going through the same process worldwide, changing not only their behaviours, but also their appearances to suit their needs, resulting in different types of orcas in different places. These different types of orcas are not yet considered different species, so instead we consider them different ‘ecotypes’. There are ten known orca ecotypes at the time of writing – five in the northern hemisphere, and five in the southern hemisphere – each fitting their own ecological niche.
We are fortunate in the Salish Sea to be home to three orca ecotypes: the resident orca (specifically the southern resident orca), the transient (also known as Bigg’s) orca, and the offshore orca. The offshore orca are seldom-seen and poorly understood, so These two ecotypes look and seem to act very similar, but there are a few subtle differences between them, if you know where to look!
Appearance:
The first thing most people notice about orcas is their dorsal fins. At around 6ft tall in a large male, they rise high above the water level when the orca surfaces to breath, making them noticeable from a fair distance away. While unique marks and scars on these fins allow us to tell individuals apart, their shape can also help us to tell which ecotype we’re looking at. On males, the dorsal fins of the resident orca are slightly taller at up to 6.5ft, with a narrower base and a distinctive forward lean. In transient orca, however, the dorsal fins have a wider base with a straighter, more pointed shape. The transient orcas also have a slightly shorter dorsal fin, coming in at ‘only’ 5ft tall!
Another distinctive feature of orca is their black and white colouration, which serves as important camouflage for hunting. On the orcas’ backs, just behind that iconic dorsal fin, is a grey patch known as the saddle patch. In the transient orca, this forms a perfect saddle shape over their backs (though they’re not for riding!), with uniform colouration that is often heavily scarred from interactions with other killer whales. Take a closer look at the resident orca, and you’ll notice another difference: their saddle patches can be ‘open’ or uneven in shape, with varying amounts of black and grey colouration.
Diet and hunting:
Perhaps the most important difference between the transient and resident orca is their dietary preferences. The transient orca are mammal-eaters, and will target the great many seals and sea lions that have made this coast their home. They’ve also been known to hunt down other cetaceans in the form of harbour porpoises, and even the occasional sea bird! Resident orca, on the other hand, feed exclusively on fish, with a strong preference for salmon. They follow the salmon runs each year, however dramatic declines in salmon numbers have been devastating for their population.
These different diets also lead to different hunting strategies. As fish generally do not have highly developed hearing, the resident orca tend to be much more vocal than the transients, and will use echolocation to find their prey. This involves sending a ‘clicking’ sound out into the water, which bounces off the fish swimming around them, and listening for the echoes of those bounces to pinpoint the prey’s location. Transient orca, however, are much quieter. Relying on stealth to hunt means that they have to stay almost silent on approach to their prey, so while they may vocalise after the kill, they won’t risk the seals or sea lions hearing them coming!
Group structure:
Like many toothed whales, orca form strong social bonds and live in family groups. While you may have heard it said that all orca are matrilineal (meaning that the females live in family groups, with daughters staying with their mother for life under the wing of a matriarch that may be their mother, grandmother, or beyond), this is not strictly true. In transient killer whales, it has been noted that either sex may disperse from their mother, with daughters breaking off to form their own pods. This results in smaller group sizes, as pods may only contain one generation of a family. It’s also the case that their groups are more fluid, and may even contain completely unrelated females and their offspring!
Resident killer whales stick much more closely to the matrilineal structure. In fact, even sons tend to stay in their mothers’ pod for their entire lives. These groups are therefore larger than the transient groups, and much more stable, though closely related matrilines may come together to form larger social pods. Unfortunately due to their small population size this has led to some inbreeding, further compounding their endangered conservation status.
Distribution:
So why are these two orca ecotypes so different, when they live in the same environment? It’s a good question, as usually we’d expect differences like these to arise from a need to adapt to a different environment. However, the fact that these two ecotypes are both found in the Salish Sea is deceptive; their ranges follow different patterns, so are in fact distinct, if overlapping.
The resident orcas’ distribution pattern is the easiest to follow. As they chase the salmon runs throughout summer and autumn, they move into defined coastal areas known for these fish. When winter sees the salmon run end, they too move to the outer coast until spring. Transient killer whales take a different approach and as such are far less predictable. They will roam widely in search of their marine mammal prey, and have been sighted as far north as Alaska and as far south as Oregon.
So what does all this mean?
It’s clear that the two different orca ecotypes found in the Salish Sea, while they may look similar, are in fact very different. They do not interact with each other, they do not interbreed, and they do not occupy the same ecological niche, so it is of utmost importance that they are both protected and allowed to thrive as one cannot substitute the other in the food web or wider environment.
The resident orca in particular have suffered great losses in recent history, largely due to both a decline in their main prey source (Chinook salmon) and the presence of pollutants in their environment, which lead to ill health and infertility. As it stands, only around 70 remain. It is our great hope that their population will recover and that one day resident orca will again be a common sight in our waters, as the transient orca are now.
Sources used:
NOAA Fisheries Killer Whales: https://www.fisheries.noaa.gov/species/killer-whale
Further insights into killer whales Orcinus orca preying on white sharks Carcharodon carcharias in South Africa: https://www.tandfonline.com/doi/abs/10.2989/1814232X.2024.2311272
Whale and Dolphin Conservation: Meet the different types of orcas: https://uk.whales.org/whales-dolphins/meet-the-different-types-of-orcas/
Parks Canada: Protecting the Southern Resident Killer Whales: https://parks.canada.ca/pn-np/bc/gulf/nature/ocean/erds-srkw/epaulard-killerwhale
Smithsonian Magazine: A Tale of Two Orcas: https://www.smithsonianmag.com/science-nature/tale-two-killer-whales-180967358/
Orca Conservancy: The Three Ecotypes: https://www.orcaconservancy.org/learn
Center for Whale Research: Three types of killer whales in the Northeastern Pacific Ocean: https://www.whaleresearch.com/post/three-types-of-killer-whales-in-the-northeastern-pacific-ocean
Center for Whale Research: About Orca: https://www.whaleresearch.com/aboutorcas