Black and White assassins- The Facts

Killer Whale Orcinus orca

The Killer Whale, Orcinus orca, is a top predator found in all oceans, however not as frequently seen in tropical waters.  O. orca can be split into three sub groups as a result of factors including prey choice, location and family size and structure. Transient Killer Whales are primarily smaller groups and target mammalian prey such as seals, dolphins and whales. Typically coastal in territory their movements are far less predictable as prey learns the location of pods and moves to new territories. To communicate cryptic echolocation is used to try and disguise their location and intentions from prey.

Killer Whales which fall under the category of Resident, in contrast to the terrestrial sub-group, live in larger groups and their primary food source is fish, specifically salmon. Loud burst of echo location are used to try and locate fish. They are also coastal living species living in deep water, however they are far more predictable due to a reliable source of prey.

Very little is known about the offshore species of Killer Whale except, again, they are fish eaters and live in the deep sea. Being sexually dimorphic, males will have larger dorsal fins up to 9.8 metres in height.

There are different ways to follow and study the whales, one used is the “following technique” where dogs are specifically trained to follow whale faeces while they are photographed and recorded to give an idea on group size, how often they feed and other behaviour.  Other techniques include satellite tracking where a tag is put onto the dorsal fin in order to follow the whales and collect behavioural and biological knowledge.

In Patagonia transient Killer Whales have shown examples of cultural behaviour, this is behaviour not inherited but learnt. They will beach themselves in an attempt to catch seals off guard. Typically the dominant and oldest female will take the pod in search of food as she has the greatest knowledge of where prey is and how to hunt it.

PCBS have effected populations of resident Killer Whales, because these pollutants are now having a knock on effect to Salmon populations which means with a severe decline in population, Orca numbers also suffer. PCBs also have a direct effect on Orcas and their health they are known to lower immune systems, cause reproductive failure, no calf has been seen partly as a result of this in the Shetland Isles for 20 years. Ecotourism is also having an effect on population numbers, as increased tourism is putting the whales under stress and affecting their behaviours, therefore reducing population numbers. Being an apex predator the killer whales have been able to adapt to their surroundings through, group cooperation, opportunistic behaviour and high intelligence.