Transient Killer Whales Gather Off Coast To Hunt Whale Calves

Thursday, April 21, 2005
MONTEREY, CALIFORNIA - The whales are back in town and they're putting on quite a show.

A bumper crop of gray whale calves migrating up the coast has drawn at least four killer whale feedings in Monterey Bay in the past week.

Heidi Tiura, co-owner of Sanctuary Cruises in Moss Landing, witnessed a gruesome orca attack on Saturday.

"It was brutal," said Tiura of watching an estimated dozen killer whales take down a gray whale calf. "They just log rolled it, ramming and thumping it with their tails. It was nature at its rawest. It's like someone grabbed your heart out of your chest and started squeezing it."

Tuesday morning, Carmel resident Robert John reported seeing a similar attack less than 100 yards offshore from the Carmel River's mouth.

"It was quite a drama" said John, who watched the attack from shore. "The water was just white with foam from all of the thrashing going on. The orcas were practically airborne at times. Normally you only see something like this on a Nature Channel."

The recent attacks are due to an unusually high number of gray whale calves migrating from Mexico to Alaska this spring.

Wayne Perryman, a biologist with the National Marine Fisheries Service, heads a counting station for northbound gray whale calves at Piedras Blancas, a point just south of the Monterey County line.

"There will be 1,200 to 1,400 calves that will pass through Monterey during this year's season," said Perryman, noting last year's comparable total of 1,500 calves was the highest his agency had seen since they started counting a decade ago.

"Reproduction varies pretty wildly in this population. One year we only had 150."

Perryman believes that recent increases in gray whale reproduction are related to warmer weather in the Arctic. According to Perryman, delayed ice coverage in the Bering Sea the past two summers has allowed gray whale mothers extra time to fatten up before their long trip south to their Mexican breeding grounds. The whales usually fast through the fall migration and the winter in Mexico, making a thick blubber layer essential to surviving the long months without food.

"They don't seem to be carrying their pregnancies to term if they don't get enough to eat," Perryman said.

Nancy Black, a research biologist with Monterey Bay Whale Watch, has been studying transient killer whales in Monterey Bay for the past 17 years. While no killer whales make a year-round residence in the bay, Black has identified 120 individuals that travel from Southern California to Oregon and seem to frequent the bay during gray whale migrations.

"Of the 120 transients off the West Coast, 60 to 70 percent will be seen in Monterey Bay looking for the gray whales during migration," Black said. "For the last week and a half, we have seen orcas every day, either feeding or searching for food."

According to Black, the open-water crossing of Monterey Bay offers a unique opportunity for the 10-ton predators to feed on calves that otherwise hug the shoreline.

"All the way from Mexico to Alaska, this is one of the very few places where orcas have a chance to catch the gray whales," Black said. "It's only a little blip in the gray whales' migration, but it's really quite a treacherous crossing. The killer whales seem to know where to be at the right time to catch them."

Steph Dutton, co-owner of Sanctuary Cruises, agrees.

"They show up on a clocklike basis to pick off the calves as they cross the bay," Dutton said. "The least experienced mothers seem to chase their babies directly across the bay. The more experienced ones hug the shoreline."

According to Bruce Mate, director of Oregon State University Marine Mammal program, sticking close to shore is a good tactic to hide from killer whales.

"(Gray whales) stay closer to shore to avoid killer whale predation," Mate says. "They can hide from view in the kelp beds and also use the noise of the surf zone to hide in the static from the orcas' echolocation. If you're out at a coastal headland, you can pitch a rock further out than the whales."

Mate is currently studying the effects of killer whale predation on young gray whales. To that aim, he put satellite transmitters on 16 gray whale mothers in Mexico this winter. The majority of Mate's whales are still south of the border and expected to be moving up the Central Coast in the next couple of weeks. Mate will keep tabs on the whales as they move north. When they reach Oregon, the northern range of the transient orcas, he will physically locate each mother to see if it is still escorting its offspring.

"We say that only half make it to become a yearling, but no one has been able to accurately estimate mortality before," Mate says.

A 2004 population survey conducted by the National Marine Fisheries Service estimates there are more than 18,000 gray whales moving between Alaska and Mexico each year. A 1998 estimate put the population at 26,000 before large die-offs during the 1999 and 2000 migrations. The current number of whales is still considered to be high and the gray whale remains the only whale, once endangered, to be removed from the federal endangered species list.

Other populations of gray whales have not been so fortunate. According to Fisheries researchers, a second population of gray whales found off western Russia is down to about 100 individuals. A population of gray whales once found in the Atlantic is now extinct.

For orcas and humans alike, the next couple of weeks should be the best time to see calves passing through the bay.

"Right now, there are probably 40 cow-calf pairs passing through each day and we haven't reached the peak yet," said Perryman. "The next two weeks should be humming."

Source: The Monterey Herald