When to Use These Terms and What They Mean
I have a big pet peeve. Anybody who is interested in killer whales knows about the different ecotypes/subspecies and the most well known of these are the resident and transient (sometimes called Bigg’s) killer whales. However, I see these names used in ways which are not correct and I see people apply the names to populations of killer whales where it is not appropriate! I want to clear up some misunderstandings surrounding the names of these groups.
Resident Killer Whales
Resident killer whales reside exclusively in the North Pacific Ocean. There are 4 populations in North America: Western Alaska residents, southern Alaska residents, northern residents, and southern residents. There are also populations of residents in Russia and Japan but they are not well studied. These whales are piscivores and only eat fish. They do not consume marine mammals whatsoever. Additionally, the name ‘resident’ itself is a bit of a misnomer! They were originally given this name by Dr. Michael Bigg, who discovered there are different types of killer whales. He named them ‘residents’ because he noted they were frequently found in a relatively small geographic area. However, populations of residents can range widely and they do not necessarily stay in one region all of the time. Their travels largely revolve around finding food and finding other whales to socialize with.
The most common mistake I see people make is applying the term “resident” to any type of killer whale that eats fish. This is not accurate. “Resident” only applies to the aforementioned groups of whales. They are considered a unique subspecies (still unnamed) and are genetically distinct compared to other killer whale ecotypes. This is why we don’t call other fish-eating populations of killer whales “residents.” They do not belong to that subspecies.
I also see people use “resident” when talking about groups of killer whales that are local and have a restricted range, such as the West Coast Community of killer whales found in the United Kingdom. People, even news organizations, frequently refer to them as a “resident” pod of whales because they do not tend to stray very far from local waters. I would dissuade people from using this term and instead refer to them as a local pod rather than resident as I think this may add more confusion to the term.
Transient Killer Whales
Like resident killer whales, transient killer whales are also restricted to the North Pacific. Well-studied populations include the West Coast transients, Gulf of Alaska transients, and AT1 transients. Other transient populations live in Western Alaska and there are likely some in Russia and Japan. Unlike resident killer whales, transients do not eat fish and feed primarily on marine mammals, such as seals, sea lions, dolphins, porpoises, and baleen whales. They will also eat seabirds and cephalopods on occasion. Dr. Michael Bigg was also the one to christen these whales as “transients” because during his study, they were elusive and seemed to roam larger ranges than residents do. “Transient” can also be a misnomer. Transient killer whales do have larger ranges than most resident killer whale populations but they can sometimes become “resident” when they find a particularly good source of food. For example, transient killer whales used to be a fairly uncommon sight in the Salish Sea and residents were seen on a daily basis. Due to shifts in prey availability for both populations, their “residency” patterns swapped. Transients took advantage of the plentiful seals and porpoises and can now be seen nearly every day in the Salish Sea, while southern resident sightings are far scarcer due to fact the whales are having to travel elsewhere to find food. The name “transient” is not necessarily indicative of where they go and how long they stay in a region.
Again, like with residents, it’s very common for people to apply the term “transient” to any population of mammal-eating killer whales, such as those in Patagonia or other regions of South America. Transient killer whales are also classified as an unnamed subspecies and thus their name is not applicable to any other population.
There are many killer whale populations in the world that are still poorly known and studied very little. Though we have classified 10 distinct ecotypes (and are now splitting some into subspecies), the taxonomy of killer whales as a whole is still unresolved and up for debate. There is even debate on whether or not type 1 and type 2 North Atlantic killer whales are “true” ecotypes. We have a very good understanding of the diet, evolutionary history, population dynamics of resident killer whales and transient killer whales but we are still learning about other populations around the world. It is very hard to place these whales into categorical boxes and we can’t simply call them “transients” or “residents” based on whether or not they eat fish or mammals (some eat both! Some eat reptiles! Some eat birds! Some eat anything they can find!) or whether or not they hang out in particular areas for long or short periods of time.