A distinct population of orcas in the north-east Pacific has been found to hunt sharks, a tough diet which wears down their teeth.
As a species the orca has a very varied diet, but different orca populations are known to specialise in hunting different types of prey. For example, in the north-east Pacific, ‘resident’ orcas feed on fish, particularly salmon, while ‘transients’ specialise in marine mammals such as sea lions, other cetaceans and even large whales.
Now a third type, the ‘offshore’ orca, has been shown to hunt sharks, providing the first evidence of the preferred prey of this population. The study, published in the journal Aquatic Biology, also found that the teeth of offshore orcas were typically worn right down to the gums – damage which was most likely caused by the tough, abrasive nature of shark skin.
Although further research is needed to determine whether these shark-eating orcas are as specialised as other orca groups, the findings of this study add weight to growing calls for different types of orca to be recognised as distinct species.
Not only do different types of orca specialise in different prey, but the distinct groups also vary in appearance and behaviour, and do not interact with each other. Recent studies have also highlighted genetic differences between them.
If the different types of orca are indeed found to represent separate species, it will have important implications for the conservation of these charismatic predators.
Liz Shaw, ARKive Species Text Author