It was early May, a time when the epic gray whale migration to the Arctic had reached the Unimak Pass entrance to the Bering Sea. A group of killer whales swam excitedly back and forth in a patch of ocean off Ikatan Peninsula in the Aleutian Islands, about 650 miles southwest of Anchorage.

There were four or five of them -- all members of the secretive type that hunts only marine mammals -- and they appeared highly agitated. Soon one of the 10-ton, black-and-white predators breached from the sea near a boat with human observers, riding the swell about two miles off the wild, uninhabited coast. What was going on?

The answer -- and the kill -- came fast.

An adult killer whale suddenly surfaced with its jaws clamped tight on the snout of a gray whale calf, an animal nearly as large as itself.

"The calf wrenched itself free, but another killer whale immediately grasped it again in the same manner," the scientists reported in a study published last week in the journal Marine Ecology Progress Series. "The (two) killer whales held the calf with its blowhole inverted for several minutes until it released a mass of bubbles, stopped moving, and slowly submerged, apparently dead."

A ground-breaking, four-year research project has found killer whales using sophisticated and cooperative techniques to intercept, isolate and then kill young gray whales part-way through their annual 5,000-mile trip to summer feeding grounds in the Bering and Chukchi seas.

The team of scientists from Alaska, Washington and British Columbia also watched killer whales actually transporting their dead prey for miles along the shore -- apparently with the goal of storing tons of blubber and muscle in shallow water so they could return later and continue to feast. The predators gathered at dozens of carcass sites, revealed at the surface by oil slicks and a ripe smell.

It was the first time any whales have been documented caching food, a behavior common among terrestrial predators as dissimilar as bears or alligators, but reported only once before for a species of marine mammals, Antarctica's Weddell seals.

The annual gathering of killer whales to ambush gray whales traveling along the Pacific Rim sends ripples through the local ecosystem -- forcing gray whales to hug the coast, concentrating birds and scavengers, attracting enormous sleeper sharks from the abyss and drawing brown bears to beaches when hunks of reeking flesh wash up high and dry.

It shows, the scientists said, how the ocean's top predator might play a "central role" in the structure of the North Pacific's marine community.

These "killer whales have developed a unique set of culturally transmitted social and foraging behaviors that appear to be shaped by the behavior and distribution of their marine mammal prey," the scientists wrote.

"The carcass-storing behavior described here relies on shallow depths around Unimak Island and provides a way for killer whales to utilize a greater proportion of prey carcasses than they would in a single feeding bout, increasing the benefit of preying on large and potentially dangerous species."