All wild animals must hunt to survive; it’s the natural order of things. But it’s sometimes tricky for scientists to understand the techniques that different animals use to ensure their success in this department. As if studying the hunting habits of ground-based animals wasn’t challenging enough, researchers have their work cut out for them when they take to the ocean to explore that of marine animals.

While ground-based animals hunt in an easily-observed environment, marine animals don’t. In many cases, marine animals dive deep beneath the ocean’s surface to a place that isn’t readily visible from a boat. Given the circumstances, researchers are often compelled to use alternate methods to track marine animals’ hunting habits.

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Researcher Jennifer Tennessen of the National Oceanic and Atmospheric Administration (NOAA) and her colleagues recognized these challenges. To study the hunting habits of killer whales in the Salish Sea, they attached tags to 21 killer whales to track their movements as they hunted. Their findings, which have been published this week in the Journal of Experimental Biology, expose some surprising conclusions.

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After analyzing the data feeds from each of the trackers, the researchers quickly caught on to the whales’ captivating hunting behavior. Upon detecting potential prey, the whales would position themselves just right for a 50-300-meter descent, after which they’d spend between seven and 10 minutes below the ocean’s surface chasing their prey.

The data revealed that the prey chases weren't always a walk in the park. Out of at least 126 pursuits, the whales sometimes performed partial barrel rolls and rapidly shifted direction to keep up with their prey; but even after such an exhausting chase, their catch success wasn’t always absolute.

The researchers were somewhat astounded that the whales’ success rates weren’t higher given the vast amounts of energy consumed during the high-speed pursuit. Animals typically conserve their energy unless they know there’s a high chance of a reward to be had from the expenditure.

Not only did the findings reveal that male killer whales hunt more often than females, but they also showed that the test subjects ate their prey in different ways. While some of the whales waited until they returned to the ocean’s surface to eat their catch, others opted to eat as they ascended. The researchers believe that the male killer whales foraged more often than the females because they have greater metabolic needs to keep up with.

In addition to teaching researchers more about the behavioral patterns of a specific population of killer whales, the study underscored an important fact: the notion that surface-based observations aren’t as practical as sub-surface observations. By directly studying the whales’ behavior below the surface, the researchers could better understand the animals’ successes and failures and discern how they hunted, which is something that can’t be seen from above.

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Perhaps future studies discern whether other killer whale populations exhibit similar hunting habits or not; after all, this research was particularly limited to just 21 test subjects in a single region, and other communities could perform differently based on factors such as prey availability and environmental disturbances.

Source: EurekAlert, Journal of Experimental Biology