Humpback whales intervene in killer whale hunt
A BBC/National Geographic film crew have recorded rare footage of humpback whales intervening in a killer whale hunt.
Gray whales migrating along the coast of California, US are often targeted by orcas.
One mother and calf's journey was being filmed for the BBC series Planet Earth Live when the third party became involved in the drama.
Onlookers suggest they were deliberately disrupting the hunt.
"To be honest we weren't expecting to see anything - it was our very first day out on the boat," said Victoria Bromley, a researcher with the crew that witnessed the scene.
- Gray whales undertake the longest annual migration of any known mammal, a round trip of about 20,000km or more
- Humpback whales perform spectacular displays of breaching (leaping clear of the water) and males sing a complex song that can last for days, in order to attract a mate
- Killer whales are actually the largest species of dolphin
"It was a massive stroke of luck when we received the call about the attack."
Working from a whale-watching boat from Monterey Bay Whale Watch, the team set up to film in an area known for sightings of gray whales.
Every year female gray whales travel north from the birthing waters off the coast of Mexico to the nutrient rich waters of the Bering Sea with their calves.
Along the route, they are targeted by orcas, which co-ordinate their attacks - aiming to separate the defenceless young from their mothers.
To minimise their risk from the predators, gray whales swim in relatively shallow water but at Monterey Bay the whales must swim over the Monterey Canyon that in places can reach two miles deep.
The film crew arrived at the scene of the hunt following a tip off call from a sister boat.
Using a camera mounted on the boat, Ms Bromley told BBC Nature: "we saw a lot of grey shapes in the water and quickly realised they were humpbacks."
According to the crew the additional whales were not just observers of the hunt but were actively involved.
End Quote Alisa Schulman-Janiger California Killer Whale Project
They deliberately stayed in our area, loudly announcing their presence”
Humpback whales are known for their impressive range of calls, including a high-pitched "trumpeting" noise made when they are agitated.
The humpbacks at Monterey Bay were trumpeting, diving and slapping their pectoral fins against the water.
"It didn't seem at all like they were confused… they were definitely there with a purpose," said Ms Bromley.
Shortly after the crew arrived the orca successfully caught their prey. The mother whale fled the scene but the humpbacks remained.
"I have never seen anything like this before," said marine biologist Alisa Schulman-Janiger who accompanied the filmmakers.
Mrs Schulman-Janiger has studied California killer whales since 1984 and is currently the director of the American Cetacean Society/Los Angeles Chapter's Gray Whale Census and Behavior Project.
After the attack, two humpback whales moved into the area where the calf was last seen alive. They continued to make trumpeting calls, rolled in the water and slashed their tails aggressively at killer whales that came near.
According to Mrs Schulman-Janiger the whole encounter lasted seven hours.
"An extraordinary number of humpback whales had appeared "overnight", feeding within a five mile area: about 100 humpback whales - converging on an abundance of krill that had grown concentrated after two days of very strong winds," she explained.
"The whales [we watched] should have been off feeding: instead, they deliberately stayed in our area, loudly announcing their presence."
The researchers have sent photographs of the humpback whales to a research centre for identification against the North Pacific humpback whale catalogue.
"Female humpback whales would be expected to react much more strongly to the protection of a youngster," said Mrs Schulman-Janiger.
"This was not a curious approach by these humpback whales: they seemed truly distressed."
Planet Earth Live continues on Wednesday 1930 BST on BBC One.