(This article was originally published on OceanLines on August 22, 2008.)
A new study conducted under a permit to La Laguna University in the Canary Islands revealed the long unknown hunting and diving tactics of pilot whales. Unlike the emperor penguins, who slow their heart rate down to remain underwater longer, pilot whales spend all their energy on one single high-speed dive that can reach depths of 1,000 meters and last up to 15 minutes long.
They make colossal dives and must come back exhausted,” said Natacha Aguilar de Soto, the study’s lead author. “They have to spend time at the surface catching their breath before undertaking a new sprint to catch prey.”
They prey on large deep-sea squids. Four foot long tentacles have been seen dangling out of the mouths of pilot whales after dives, but Mark Johnson, an engineer at Woods Hole Oceanographic Institution, says that they have “found pieces of the arms of giant squid, Architeuthis dux, floating where the whales are coming up. We have always imagined sperm whales hunting giant squid but maybe these tough pilot whales, one third the size of a sperm whale, are the ones showing up for the fight.”
A typical dive begins with a descent of 500 meters. At that point the whale levels off and selects a target. The actual chase can then take the whale down to 1,000 meters. Most deep-diving whales, including the beaked whale, will only descend at speeds of 1-2 meters per second which allows them to conserve energy and maximize time spent underwater. Some beaked whale dives can last up to an hour. They catch more prey of a smaller size this way.
“We didn’t expect such differences in the tactics between deep-diving squid-eaters,” said Johnson, who designed the tagging devices used in the study to record sounds in the deep waters.
This kind of deep-sea sprinting also poses significant risks. The studies show that the pilot whale is only successful about 60% of the time and they expend almost all of their energy. This study helped to explain differences in the whales behavior on the surface. While beaked whales are hardly ever seen, pilot whales are often found in large groups on the surface. This is because the beaked whales conserve more energy while hunting so they can spend most of their time under water but the pilot whales must resurface to catch their breath and recover from their underwater sprints. Pilot whales have a reputation of being calm, relaxed, and approachable, and not bothered by boat traffic when on the surface, but it turns out that they might just be too exhausted to be scared.
To track the pilot whales researchers used the device that Johnson created, called a d-tag. It is a special non-invasive tag that allows the researches to hear the sounds, but not inturrupt the hunt. “What’s cool,” Johnson said, “is to ‘see’ how whales hunt at depth using their own sounds,–without the intrusion of lights and a camera.”
Copyright © 2008 by OceanLines