And although scientists have previously found different forms of orcas that live in separate and distinct cultures in the Pacific and the Antarctic, this new study by Dr. Andy Foote from the University of Aberdeen, UK, along with colleagues from universities and museums in Denmark and the UK, is the first to describe them in the North Atlantic.
Foote told the BBC
, that it was "exciting" to think about two very different types of orcas in British waters.
One form of orca which they called type 1, came from closely related populations and is a "generalist type which reaches up to 6.6 m in length." The type 2 whale on the other hand, was more closely related to Antarctic whales and is "a highly specialist type, reaching up to 8.5 m in length."
And the differences didn't end there.
After examining the teeth from mammals stranded over the past 200 years, the scientists also discovered that each type of North Atlantic whale had different teeth wearing. Type 1 orcas, seen to generally feed on fish such as herring, mackerel and seals, had teeth that were well-worn; yet type 2 orcas that consumed whales and dolphins, showed barely any wear at all.
Photographs show that even their eye patches are different; type 1 orcas have a parallel orientation with the anterior end in front of the blowhole:
Yet in type 2 whales, the eye patch has an angular orientation and the anterior end is behind the blowhole:
In the eastern North Pacific Ocean, three distinct types of orcas have been recognized and well documented: residents, transients, and offshores. Resident whales are very different from transient whales, they primarily eat fish, have a rounded tip on their dorsal fin and display varying saddle patches with five identified patterns. Resident whales are maternal mammals and travel in matrilineal groups.
Transient orcas on the other hand, are less maternal, have a more erect dorsal fin tip and a saddle patch pigmentation that is restricted to just two patterns. They feed almost exclusively on marine mammals. The differences between these orca types is so diverse, that some scientists have suggested that they should officially be designated, distinct species.
Foote told the BBC, that the divergence he's seen in the UK's North Atlantic orcas, could eventually lead to type 1 and 2 whales evolving into different species; Digital Journal asked Dr. Foote about similarities between the two ecotypes in the Pacific/Antarctic and their counterparts in the North Atlantic:
There are some potential similarities. We did some analyses last year on the genetic sequences for killer whales worldwide and that suggested that the resident ecotype had probably moved from the Atlantic into the Pacific several thousand years ago, and then come into contact with the transients.
The long separation, said Foote, "may have allowed for the differences between them to accumulate slowly over time, or once they came back into contact," and "the change in competition could have promoted them to specialise on different prey."
Unfortunately suggested the orca expert:
We know a lot less about the whales around the UK; but from the museum samples we looked at we found differences in the tooth wear - some had very worn teeth and some had almost no tooth wear. The orcas without tooth wear were most closely related to 'type A' killer whales from the Antarctic, and so it seems that in this case there was also a period of separation, (and then coming back into contact again), which led to the evolution of different types of killer whale.
Type-A, Antarctic killer whales
are large orcas; males can grow to almost 30 feet in length and weigh up to 10 tons. They are typically found in more open water and their prime prey is minke whale.
Unfortunately suggests Dr. Foote, until scientists can learn more about the orcas in the North Atlantic, the comparisons will remain a bit one-sided.
"We know a lot less about the ecological differences," Foote told Digital Journal, "as we still don't know much about the diet of the ones with no tooth wear. We also only looked at the maternally inherited DNA and so we don't know if they are inter-breeding," he added. As a result Foote says, "We know much more about the residents and transients than we do about these types around the UK."
The discovery shows how orcas have evolved and adapted to their environment. An act that could have important implications for how they are monitored by conservationists suggests Foote. "It's similar to how Darwin's finches have adapted to different ecological roles in the Galapagos, but on a larger scale," he told the UK's Daily Telegraph
The scientists published their results in the journal Molecular Ecology