Killer Whale Expert Presents Research

Tuesday, April 25, 2006
KODIAK, ALASKA - Transient killer whales may be stealthy, silent types, but they vocalize enough for acoustic researcher Volker Deecke from the Vancouver Aquarium in British Columbia to identify who’s talking and what they’re likely to eat for dinner.

Deecke presented some of his research to more than 50 Kodiak residents at Kodiak College Friday evening. Deecke’s talk was the last in a series of original research discussions brought to Kodiak as part of Whale Fest 2006.

Deecke stressed that the animals most people call killer whales (orcas) are two separate species: transient killer whales that eat mammals, and resident killer whales that eat only fish. The two types live side by side in the same waters but do not interbreed, although the latter point is still open to debate, he said.

While eavesdropping on underwater whale vocalizations, researchers discovered that keeping track of transient killer whales is a lot harder than monitoring residents.

Resident killer whales keep up a constant racket while they’re fishing.

“You can go out for a few hours and tape enough calls to keep you busy for months,” Deecke said.

“For the meat eaters it’s a trade off — they either eat or talk,” Deecke said, so field data is hard to come by.

Transients are after a smarter prey, so they hunt silently. The only time you hear them is after they have made a kill or when they are splashing sociably at the surface, Deecke said.

Even their travel patterns make them elusive. Resident killer whales follow salmon runs, but transients depend on surprising their prey.

“It is easy to lose them,” Deecke said.

Deecke identified four transient populations for his Kodiak audience.

The West Coast transients are a group of 220 that range from Monterey Bay in California to Glacier Bay in Southeast Alaska. These whales prefer harbor seals over other prey. Sea lions, porpoises, dolphins and minke whales supplement a diet that is almost 60 percent harbor seal.

In Kodiak, transient whales dine almost exclusively on Steller sea lions which comprise 92 percent of their diet. The Gulf of Alaska population, with its 32 identified individuals, turns to Dall’s porpoise for the other 8 percent of its food.

But this information is based on “a puny total of 13 predation events made around the Kodiak harbor,” Deecke said in a phone interview today. “It is certainly an overestimate.”

Prince William Sound is home to the AT1 transient population, a small group of five individuals expected to go extinct soon. These transients prefer harbor seal and Dall’s porpoise equally. Much of their diet is unidentified; but, Deecke said, researchers have never documented a Steller sea lion takes by this population.

Most research on transient killer whales on the West Coast has been done nearshore and covers areas from the Gulf of Alaska south.

“Offshore research is expensive,” Deecke said.

A few researchers, including killer whale authorities Craig Matkin and John Durban, are venturing out west to False Pass and beyond. There they are beginning to collect data on the Eastern Aleutian population.

Their research indicates that 72 percent of the Eastern Aleutian transient diet comes from gray whales, mostly calves, Deecke said.

Though researchers have never seen these transients kill a gray whale, several photos show them feeding on blubber dragged to the surface. Deecke believes predation takes place at night.

Local whale expert Kate Wynne marveled that Deecke has matched an individual resident whale to its matrilineal family group after hearing a recording of its calls over the telephone.

Deecke said fish-eating residents can sometimes be matched by dialect to a group as small as 20 individuals, but researchers can’t do this with transients. After all, he pointed out, residents talk all the time. Transients are silent 95 percent of the time.

Although transients use the same types of calls that resident populations use, Deecke characterizes their pulsed calls as more “melancholy and whiney.”

These pulsed calls can be heard as far away as 20 miles.

Killer whales also use precise echolocation clicks to orient themselves and high-pitched whistles to greet nearby groups of other whales.

Resident killer whales seem to attract mates outside their family gene pool by vocalizing a different dialect, Deecke said. But it will be a while before researchers can identify transients so precisely.

The two points Deecke stressed are that transients in the North Pacific show a high degree of dietary specialization and that their survival depends on silence.

“It’s a trade-off, they either talk or eat.”

Often you don’t hear a thing until they’ve made a kill, Deecke said.

Source: The Kodiak Daily Mirror