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Killer Whales—Killing Other Whales

Anne Marie Hammers
for National Geographic Today
March 24, 2003
 
Every day this spring, Nancy Black and her research partner Richard Ternullo will scour the seas for transient killer whales—roamers who prey in packs and count as the deadliest of their species.

During April and May transient killer whales frequent Monterey Bay, and that's when Black, an independent marine biologist who also runs the Monterey Bay Whale Watch, sees the highest numbers of predatory attacks.

That's because gray whales are gliding through these waters during their migration from Mexico to the Bering Sea. The transients ambush them—they have a taste for the gray whale calves' high-energy blubber and protein-rich tongues. Black's goal is to catch a glimpse of the feeding frenzy.


Researchers have identified three types of killer whales, or orcas, along the U.S. Pacific coast: offshores, residents, and transients. Little is known about offshores, rarely seen deep-sea denizens. Residents are the most familiar—their gregarious socializing and aerial acrobatics thrill whale-watchers.

Transients are "a breed apart"—elusive killers that rove over 1,500 miles (2,400 kilometers) of coastline from California to Southeast Alaska.

"The transients are so different in behavior, diet, and even genetically from fish-eating residents that many scientists believe they could be a distinct species altogether," said Black.

Cooperative Killers

Killer whales are top predators—kings of the sea, with no natural enemies other than humans. They have distinctive black bodies with white patches, particularly over the eyes and around the belly. Females grow to about 26 feet long (8 meters); males, 28 feet (8.5 meters).

Because the transients are such gypsies, their so-called "predatory events" present the best opportunity to study them. A gray whale kill can last up to 13 hours.

Last spring, in a rare, wild showdown, a group of transients killed a gray whale calf in the Monterey Bay. Tipped off by a local fisherman, Black arrived at the scene in her inflatable boat to find scattered chunks of whale blubber, intestines, ravenous sea birds—and an unusually large group of 25 transients.

"The killer whales actually work together as a team to take down a gray whale," said Black. After they killed the whale—in what looked like food sharing—one killer whale held down the carcass as the others tore the thick, resilient gray whale skin and blubber.

Black focused on one aspect of the group kill: how transient mothers and their calves interacted.

"It's a perfect opportunity for the calf to gain the experience it needs to learn how to hunt a gray whale and then feed on it later on," Black said. Killing a large whale is too dangerous for the calf, but as a spectator, it picks up lethal techniques like ramming, drowning, and biting the prey.

But even skilled teamwork may not ensure a calf's survival. In recent years, scientists revealed that resident killer whales were heavily contaminated with deadly toxic chemicals.

Toxin Buildup

"Residents are showing up with immuno-deficiency problems, reproductive incompetence, and some adolescent males are dying off," said Ken Balcomb, a marine biologist for the Center for Whale Research in Friday Harbor, Washington, who has studied killer whales since 1976.

"The average life expectancy for a male resident is 29 years, but lately adolescent males are dying from age five to late teens," Balcomb said.

To learn more about the toxin levels and determine the general health of this species, Black is taking blubber samples of the transients as they feed on the gray whale carcass.

Black uses a four-foot-long (1.2-meter-long) dart gun to get her sample. She is one of a select group of scientists permitted to take blubber samples from killer whales.

Black sends the samples to the Northwest Fisheries Science Center in Seattle, where technicians analyze blubber for organochlorines (OCs) which are toxins like PCBs and DDT.

New results from Gina Ylitalo, research chemist at NWFSC, reveal disturbing news. "California animals contain the highest levels [of Ocs]. OC concentrations in transient killer whales were much higher than those found in residents or—offshore whales," Ylitalo said.

Life at the top of the food chain has its liabilities.

"The fish in the oceans transfer those chemicals over here and (since) killer whales are the top predator and they're eating seals, sea lions, dolphins and whales, they're bio-accumulating those chemicals," Black said. "They end up with the highest levels of all."

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