Killer whales suspected in deaths of 3 humpbacks

North Gulf Oceanic Society researchers first spotted the dead humpbacks Sunday near East Chugach Island, Pearl Island and Kachemak Bay.

"Definitely, there's been killer whales on these humpbacks and it's thought they were preyed upon by killer whales," said Barbara Mahoney, a biologist with the National Marine Fisheries Service.

But did the killer whales actually kill the humpbacks, or did they just happen on the carcasses and feed on them?

Officials from the oceanic society, the fisheries service and the Alaska SeaLife Center are working together to figure out this marine mystery.

A team of oceanic society researchers saw a group of 11 killer whales harassing six humpbacks near islands in the northwest part of the Gulf of Alaska on July 11. No blood was shed, they reported.

Some killer whales kill other whales and some don't. Transient killer whales do.

The group the researchers spotted are the only reported transients in the area, making them suspects, Mahoney said.

The 30- to 40-foot-long dead humpbacks have the markings of killer whale predation, she said. All three are missing their tongues and some have lost their lower jaws, pieces of their throats, or have scraped noses.

"This is a bit surprising because they are humpbacks," said Craig Matkin, director of the oceanic society. "We just haven't seen much predation on adult or real large juvenile humpbacks in Alaskan waters." The transient, mammal-eating killer whales typically feed on gray or minke whales, he said.

The damage to the dead humpbacks is not enough to prove that killer whales killed them, said Dawn Kimberlin, spokeswoman for the SeaLife Center. Killer whales sometimes feed on dead humpbacks, she said.

Other explanations for the deaths include the naturally occurring and potentially fatal domoic acid, boat strikes or starvation, Kimberlin said.

There are plans to do a necropsy on at least one of the dead whales, but they are still floating in the Inlet. A necropsy won't be possible until they are on land.

Cy St-Amand, a researcher for the oceanic society, put a buoy on one of the dead whales that is marked with an ID number and a toll-free phone number for the Alaska SeaLife Center in the hope that someone will call if they find the carcasses on land.

St-Amand took skin samples and pictures of the whales' flukes to use in the investigation.

Transient, mammal-eating killer whales feed primarily on sea lions, seals, porpoises and other whales. They prey silently. They are not to be confused with the more gregarious, fish-eating, "resident" killer whales, said Kate Wynne, a marine mammal specialist with the University of Alaska.

Transient killer whales in Alaska are found in three different areas. They travel long distances from Southeast to the Aleutian Islands and the Bering Sea, from Prince William Sound through the Kenai Fjords, and from California through the waters of Southeast Alaska, according to the 2007 Alaska Marine Mammal Stock Assessments report.

Resident killer whales are known to frequent many of the same areas, but do not socialize with the transients, Wynne said.

There are about 70 or 80 transient killer whales in the Gulf of Alaska, compared to about 700 identified resident killer whales, Matkin said.

More than 10,000 humpback whales live in the North Pacific, with about 300 feeding in summer between Kodiak and Lower Cook Inlet.

Five other whale carcass sightings were reported in Lower Cook Inlet -- one only bones washed ashore -- since late June, according to oceanic society records.

The causes of their deaths remain unknown.

Find Monique Newton online at adn.com/contact/mnewton or call 257-4469.