Same animals, different country
Killer whales (orca) are one of most largely distributed mammals in the world and, just like humans, depending on where they are found they have cultural variations in behavior, diet and vocalizations.
When working in New Zealand I was lucky enough to see Killer Whales twice in the Marlborough Sounds. It wasn’t until I got to Victoria that I realized the animals I was seeing here in Canada differed to the Killer whales I saw in New Zealand, despite being the same species!
The population of Orca in New Zealand is about 150-200. They travel long distances, mainly in coastal waters, at times doing figure 8’s around the North and South Islands. It is their prey selection, however, that really sets them apart. The Killer Whales in New Zealand appear to have a preference for elasmobranchs (rays and sharks) with four main prey types; rays (the most common food type), sharks, fin-fish and cetaceans.
In the spring and summer months it is not uncommon to see Killer Whales scanning local harbors for stingray. They dig in the muddy sea floor and then herd the rays into shallow waters before the feeding begins. Passers-by have even told accounts of stingray leaping out of the water onto neighboring rocks for safety when Killer Whales are in the area. Other documented prey species of Killer Whales in New Zealand include white, blue, thrasher, hammerhead, grey reef, shortfin mako and seven gill sharks! Not to mention manta and eagle rays in addition to short -and long- tailed stingrays. This differs greatly from the pinnipeds and Chinook salmon, which are at the top of the menu for the Transient (Bigg’s) and Southern Resident Killer Whales respectively, here in the Salish Sea.
Of course with different diets come alternative hunting strategies. A Killer whale in New Zealand was reported attacking a blue shark by smashing it with its tail at the water’s surface. This behavior is thought to be an effective way to disorientate and kill sharks. Of course fraternizing with lethal prey species does have its consequences. It is reported a sub-adult female Killer Whale was found floating in the Haraki Gulf having died from wounds received from stingray barbs. Feeding on stingrays is not a commonly observed behavior in Killer Whales in other parts of the world, so it is most likely a learned behavior unique to the New Zealand residents. In this case it is believed this young female had not quite mastered the highly skilled technique required to safely kill these animals and paid the ultimate price. In addition, having other apex predators as your prey of choice will ultimately lead to a high level of bioaccumulation of toxins such as heavy metals and organochlorides. Must be a case of the higher the risk, the greater the reward!
Within the New Zealand ecotype of Killer whales there are two ways to divide the whales into sub-populations. One division uses the difference in prey selection between individuals resulting in three types of sub-population. Using the prey selection method results in one group of generalist feeders preying upon all 4 main prey types (rays, sharks, fin-fish and cetaceans), the second group is a little less opportunistic and feeds on 3 prey types and the third proposed sub-population is thought to be very specific, foraging only on cetaceans (other whales) . The alternative method for partitioning New Zealand Killer Whales into sub-populations is by geography: 1) those found in waters off the North Island, 2) those found off the South island and 3) those found off the coast of both the North and South Islands.
It is evident that the Killer Whale species is extremely cosmopolitan with a bounty of variation stemming from their widespread distribution. It is special to know that wherever you see these animals they are a unique!
Blog written by our Naturalist Emma