Killer whales are discriminating diners

Washington, Nov 9 : A new study has determined that killer whales can discriminate among the various species of salmon, which is their favorite meal, by listening to the echo structure created by each type of the fish.

According to a report in Discovery News, echolocation, which involves creating a sound in order to produce an echo, allows the whales to zone in on king salmon, also known as Chinook salmon, at distances up to half a mile.

To study this phenomenon, Whitlow Au, a marine mammal researcher at the University of Hawaii's Hawaii Institute for Marine Biology, and his colleagues, mechanically recreated killer whale echolocation pulses at Lake Union in Seattle, Washington.

The researchers tied Chinook, Coho and Sockeye salmon to a rotating net set out at different water depths.

Although these fish look similar to human eyes, the study showed the echo structure created by each type of salmon was unique and could be used by killer whales to discriminate among the various species.

"Fish gas" appears key to the process, as the study revealed echolocation tuned especially well into information released by each salmon's swim bladder.

"Swim bladders are gas bags within a fish that help the fish to be buoyant at any specific depth," Au explained. "Gas bags are probably the best reflector of acoustic energy underwater," he added.

Au likened killer whale echolocation to a person wearing a miner's cap with a blinking light on it. Each time the light blinks on, the individual receives information about what's around.

Among whales, only toothed species use echolocation.

Au therefore suspects other toothed whales, such as sperm whales, possess the killer whale's choosy, long-distance mealtime behavior.

ANI