In rare attack, 30 orcas 'badly wounded' 2 adult gray whales in California

Stunning new video shows a pod of orcas attacking two adult gray whales in California's Monterey Bay, in a rare case of predation. Monterey Bay Whale Watch videographer Evan Brodsky, who captured the dramatic footage March 30 using a drone, counted more than 30 orcas. The attacked whales split up and eventually made it to safety in shallower waters after a 6-hour melee, Brodsky wrote in an Instagram post.

The video, which was posted to Facebook April 2, shows the gray whales huddled together as the orcas swoop in from the sides. Monterey Bay Whale Watch said both whales were "badly wounded" during the encounter. 

Orcas (Orcinus orca), also known as killer whales, are the only major predators of gray whales (Eschrichtius robustus), according to the Alaska Department of Fish and Game. But killer whales usually hunt calves rather than adults, opting to "take advantage" of calves that migrate up the coast with their mothers in the first year of their lives, Ari Friedlaender, a marine mammal ecologist at the University of California, Santa Cruz, told Live Science. And even going after a young whale is no easy feat as the pod must still contend with its protective mother. 

That makes the newly filmed attack on the adults unusual.

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Still, one attack doesn't necessarily imply a troubling pattern, Friedlaender said. 

"A single event is really something you don't want to raise too big a flag over," Friedlaender explained.

However, if orcas continue to attack adult gray whales, scientists might see the behavior as a sign of an underlying problem, Friedlaender continued. For instance, one potential reason for orcas to continually attack adults is that significantly fewer gray whale calves are available. In that case, the attacks could signify an underlying problem with the gray whale population.

While taking on adults is a big challenge, hunger is also a potent motivator. Friedlaender said the gamble to attack two adults was a matter of "risk-reward," meaning the reward of feasting on more whale meat must be weighed against the higher risk of sustaining injury. At the moment, he said there's not enough information to determine whether the orca population is suffering from food deprivation. Should this trend continue, drone footage showing the whales' size and thickness could be a clue to their wellness. He added that orcas have been known to prey on adult blue, fin and humpback whales, all of which can grow to be bigger than grays.

Orcas can grow up to 32 feet (8 meters) long and weigh over 12,000 pounds (5,400 kilograms), according to National Oceanic and Atmospheric Administration Fisheries. An adult gray whale can reach up to 49 feet (15 m) long and weigh about 90,000 pounds (40,800 kg). Gray whale newborns are around 15 feet (4.6 m) long and weigh 2,000 pounds (900 kg).

Friedlaender said that the whale-watching community will keep an eye out for future oddities. For now, this isolated incident offers an insight into the orcas' hunting prowess and ambition. 

"It never ceases to inspire a lot of awe for the animals," Friedlaender said. "Killer whales are pretty amazing and there's nothing that's too big for them."