Friday, March 25, 2016

Killer Whale Hunting Strategies

The first thing that comes to mind for me when someone talks about orcas is Shamu. Although they look beautiful and majestic, these are not animals that you would want to get in the water with; they have the name "killer whales" for a reason. I knew a little about these animals and how they hunted in pods, but not much, so I decided to do some research on this topic

Research was done for a few years at Punta Norte on the east coast of Argentina, that primarily focused on the social dynamics of killer whales, Orcinus orca, when hunting marine mammals. These predators help to show association patterns and foraging behaviors, and paint a pattern to understanding hunting efficiencies. In general, killer whales are rather smart and clever when it comes to hunting their prey. It has been documented that a pod of these predators will swim in a line towards an ice floe that a seal is sitting on. They will create a large enough wave to tip the ice floe or flip it entirely and through the seal into the water for the whales to eat. Another strategy that has been used is when they attack an animal that is much larger than themselves. An example of this is a large number of the orcas ganging up on a baleen whale and attacking it from all sides.

The researchers for this study identified 13 different killer whales by recognizable features on their dorsal fins. The objective was to study the details of predator and prey interaction and foraging strategy of the whale population of Punta Norte. This allowed the researchers to observe the behavior of prey and predator directly, and to gain data over a span of two years. All of this data helped to indicate that the killer whales at Punta Norte hunt preferentially in the most productive areas and pursue the prey-type that is the easiest target. It was also found that whales within the same pod share food, and that one whale within each pod will do most of the hunting.

The hunting area of the orcas was divided up into 12 quadrants, each roughly 580m wide. Behavior was classified into categories consistent with earlier studies that had been done. Each time a whale would surface, it's behavior, position, and direction of travel was recorded. During 'patrol' behavior a whale would travel just beyond the surf zone parallel to the coast for roughly 20m or more. 'Hunting' was defined as nearshore intentional scanning, pursuits, close approaches and/or standing in the presence of potential prey.

A total of 13 whales were identified in three separate pods. The pod that was seen the most was made of two adult males (B-pod). The pod that was seen the second most was named A-pod and consisted of two adult females and five subadults. The third pod (C-pod) was made up of one adult male, one adult female, and two subadults. This C-pod was seen the least. This whales were seen over a two year time span and a total of 468 hours.

In general for all the pods, most of the hunting took place in quadrant 10, which had a deep channel in the middle that was surrounded by reefs. Of the attacks that were recorded, approximately 97% were directed towards southern sea lions, 2.4% were directed towards southern elephant seals, and 0.6% were directed towards birds. Of the attacks directed towards southern sea lions, the majority (65.5%) were directed towards the pups, which helps to indicate that the whales tend to go for the easier catch.

When the whales would catch a sea lion pup, it was held by an appendage and swung back and forth so that it would hit it's head on either side of the whale's head. It could also have been shaken very violently. The pup would then be taken off shore and was either not observed again, or was released and then pursued in open water by all the whales present. This helps to show that the killer whales tend to share the food with the rest of the pod.

After this study, there are several things that are now certain. These killer whales hunt in very specific locations with specific strategies, the cost of competing over high quality sites could be very high, and whales within the same pod will work together to get the prey, and then will share the food.


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