Whale Camera Spies On Hawaii's Deepwater Hunters

James Owen
for National Geographic News

February 6, 2004

This story is one of a series looking at National Geographic
Crittercam research. Crittercam is a research instrument worn by wild
animals and equipped with a video camera and other
information-gathering equipment. Crittercam is used on animals both
in the ocean and on land.

To learn more about the Crittercam's field test in Hawaii, tune in to the Crittercam: Pilot Whales episode on the National Geographic Channel in the United States on Friday, February 6 at 8:30 p.m. ET. Got a high-speed connection? Click here to watch previews of the Crittercam television documentaries on the National Geographic Channel Web site.

The pilot whales are taking a time-out. Basking beneath the morning sun, they look like a raft of giant ebony logs, with just their dorsal fins and blowholes bobbing above gently lapping waters.

It would be easy for the boatloads of passing whale watchers to get the wrong impression, for these intelligent, powerfully built animals are far from idle. This is a well earned rest they're taking, having spent the pre-dawn hours chasing squid in the deeply shelving Pacific Ocean, off Hawaii's Kona coast. It was a successful night; one they are quietly digesting.

Until now, it would have taken a feat of the imagination to get a picture of what pilot whales get up to when diving beneath the waves. But with Crittercam, and other recent technology, scientists are beginning to shed more light on these mysterious sea mammals.

Kona is on the west side of Hawaii's Big Island. A popular tourist destination, the region also attracts many of the world's whales. As well as those magnificent behemoths, humpback and sperm whales, there are beaked, killer, melon-headed, and minke whales, to name a few.

Despite their names, some of these are really types of dolphin, as is the short-finned pilot whale (Globicephala macrorhynchus). Unlike its close relative, the long-finned pilot whale, they dwell in tropical and subtropical waters. Studies off northwest Africa found they favor areas where the seabed slopes steeply, creating strong currents and upwellings, which tend to support higher prey densities.

This might explain why short-finned pilot whales live off the Kona coast all year—unusual for this oceanic species—for the seas around Big Island, a volcanic outcrop, slope steeply down to around 2,000 meters (6,500 feet).

So a good location, too, for Robin Baird, biology fellow at Dalhousie University, Halifax, Nova Scotia, Canada, and local cetacean expert Dan McSweeney, of the Wild Whale Research Foundation, Hawaii, as they probe deeper into the pilot whales' lives.

Suction Cups

Crittercam, attached via suction cups to the whales' backs, gave them an insight into the daytime diving behavior of these highly social animals which live in large pods of up to 200 animals. The ebb and flow of their daily routine appears to be dictated by the squid and fish they prey on—species that lurk near the ocean floor during daylight hours. So this is a time mainly for bonding and lazing around.

"A lot of body contact is visible in the footage," said Baird. "It also confirmed that when the animals were near the surface they did not appear to be foraging, helping to prove that it is the deeper dives that function for foraging."

He had expected this pattern of behavior, having studied long-finned pilot whales in the Mediterranean, off the west coast of Italy. It was the first time anyone had recorded the dive depths of this species in the wild.

Data were taken using time-depth recorders (TDRs). "They have a pressure sensor for determining depth, as well as a velocity meter for swim speed, and also a light sensor," Baird explained.

During the day the whales spent their time in the top 16 meters (52 feet) of the water column. But shortly after sunset they turned tail and plummeted to depths of up to 650 meters (2,133 feet). Baird says this is when the vertically migrating deep scattering layer (DSL; a sound-reflecting layer of dense zooplankton, plus fish, squid and other organisms) comes into range as it ascends under the cover of darkness.

Depth and velocity data suggested the whales then followed their prey to the surface where they continued to feed until before daybreak.

Yet the Hawaiian pilot whales also showed diving patterns that were out of sync with their European cousins. Crittercam and TDR data showed that some whales did dive deep during the day, to more than 800 meters (2,625 ft), staying down for almost half an hour. Even more surprising was the finding that nighttime activity was typically between 300 and 500 meters (984 and 1,640 feet), with no indication the whales rose to the surface to feed.

Clear Waters

Baird suggests this may be due to both the clarity of the water and the starry night sky out in the middle of the Pacific.

He said, "Information from the light sensors has been extremely useful in understanding why the dives at night were deeper than expected. Light levels at the surface at night were still substantially higher than at depth. So while the depth patterns indicate the whales are following DSL-associated prey around sunset, it appears the light levels are high enough to keep these prey away from the surface."

How these toothed whales detect prey deep in the night sea remains something of a mystery. Baird said, "Presumably, echolocation is most important, perhaps supplemented by detecting prey visually if they produce light; either actively, or by disturbing light-producing organisms in the water as they move."

Fast, intense clicking sounds produced by pilot whales, which have large, bulbous heads, rather like the nose of a submarine, have long been implicated in echolocation. Meanwhile, studies have shown that they often target luminous deep-sea squid species, suggesting they do detect prey by sight.

It's strange then, given these powers of pinpoint detection, that pilot whales sometimes seem unable to identify dry land. Mass strandings often occur. Whether illness, magnetic interference, or confused echolocation due to a gently shallowing seabed causes these catastrophic navigation failures is unclear, though the social cohesiveness of pilot whales probably doesn't help. It appears they would sooner follow the lead, or 'pilot', whale into mortal danger than break away from the pod.

Despite the dramatic new insights provided by Crittercam, we still have much to learn about these extraordinary animals.