A massive pod of up to 50 killer whales has been filmed for the first time off the coast of Scotland by a BBC crew.
Gordon Buchanan, presenter of BBC Autumnwatch, filmed the group from a fishing boat in the North Sea.
The killer whales are filmed approaching the fishing boat and feeding on mackerel that escape the fishing nets.
The tenacious behaviour reveals an unlikely alliance between fishermen and predators of fish.
Killer whales (Orcinus orca), otherwise called orcas, live in family groups called pods and occur in British waters.
As the largest member of the dolphin family, killer whales are known for their intelligence and range of hunting behaviours.
The pod of killer whales caught on camera belong to a family group that has developed a particular hunting strategy; following mackerel fishermen and feeding on fish that escape their nets.
The fishermen are really fond of the killer whales
Andy Foote University of Aberdeen
As the nets are brought to the surface and into the boat, the killer whales approach and come alongside, giving fishermen and the BBC
team a grandstand view of the pod in action.
The killer whales pick of any escaping mackerel and also feed off scraps as the nets are later lowered back into the water to be washed clean.
Scientists first documented this behaviour in the 1980s and fishermen in Scotland have seen the behaviour develop since.
"They are pretty quick to cotton on, and it's something they are doing all around the world where there is a big fishery," says Mr Andy Foote of the University of Aberdeen, a marine scientist advising the BBC Autumnwatch team.
"But what's great about this one, is they aren't viewed as a pest, they are just going after mackerel that are stuck in the nets or escaping and they don't take any of the fishermen's catch," he says.
"They don't damage the nets or get stuck in the nets, there is a benefit for both parties and the fishermen are really fond of the killer whales."
Pods of killer whales can include up to 200 individuals, due to the abundance of food provided by the fishing boats.
The mackerel-loving killer whales are thought to be a distinct family, unrelated to killer whales found in Shetland or others that hunt herring off Iceland.
The group follows the migration of mackerel from the Norwegian sea, past Shetland and down the west coast of Ireland and Britain possibly as far as the Portuguese coast.
The killer whales that feed on mackerel have been found to have very worn down teeth as a result of their feeding behaviour.
Scientists believe it is a result of how they suck up the fish one at a time. The suction, along with the abrasive nature of salt water, wears their teeth down.
Similarly worn teeth are also seen in other suction feeders such as sperm whales.
Gordon Buchanan presenter and cameraman on the BBC series Autumnwatch has been living aboard the working fishing boat with one other BBC colleague in an effort to capture the killer whales on film.
he tells how he was lucky to encounter the massive pod.
The Killer whales can be seen on the BBC series Autumnwatch, which is broadcast at 2100 BST on BBC Two on Friday 16 October.
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