Normally associated with the cooler seas around the poles, Orca whales are now becoming an increasingly common sight off the coast of UK. The Orca whale – also known as Killer whale, Blackfish and Seawolf – is found in all the world’s oceans and in most seas, including the Mediterranean and Arabian Seas. It is however known to prefer the cool waters of the polar regions, which makes this boom in recent sightings around the British Isles quite surprising for marine biologists.

This year alone, Orca whales have been spotted in locations such the English Channel, the Irish Sea, and near Hartlepool in the North Sea. The southernmost sightings in UK waters took place near the Isles of Scilly, an archipelago off the south-western tip of England.

According to Andy Foote, PhD Student at the University of Aberdeen, pods of over 100 Orcas have been seen around the Shetland Islands this summer.

“That sort of sighting does seem to be on the increase,” says Foote. “The killer whales shift their migration and distribution quite drastically. Fish like herring and mackerel seem to be doing pretty well at the moment, and it makes sense for the killer whales to follow them.”

Orca whales have been a rare sight in UK waters since fishing stocks began to decline dramatically in the mid 1900s, and the perceived increase in sightings has therefore been interpreted as a sign of recovering fishing stocks. It is however hard to know anything for sure yet, since no records of Orca sightings exists from earlier years. Researchers from the University of Aberdeen and the Sea Mammals Research Unit at St Andrews are currently monitoring the waters off Scotland, to investigate if the increase in sightings is correlated to an actual increase in Orca whales in UK waters or if it is simply the result of better recording methods.

During the second half of the 20^th century, Orca sightings in UK waters have normally been viewed as transient animals migrating through the area, but researchers have now been able to determine that the same individuals are in fact recurrently spotted off the British coast, by comparing 2008 sightings with photographs taken of Orca whales over the past decade.

“Until now, very little has been known about them in British waters, Foote explains. They have been considered as being transient and occasional animals that just move through the area. People thought they were very infrequent visitors. The fact that we are seeing the same ones year after year after year shows that that is wrong. Already we have highlighted that we have populations which are resident here for long periods of time, coming back to the same place, year after year after year, while some seem to remain all year around.

Paul Harvey from the Shetland Biological Records Centre agrees with Foote. “We are definitely seeing more. We know we’ve got the same animals returning and we have some occurring here throughout the winter. It is a relatively recent phenomenon. If you talk to fishermen, they just didn’t used to see them. Now, they see them every time they haul their nets. Something has gone on, since about the 1990s, when we first started to see more. We don’t know how many pods we are dealing with. That is the value of the new research.“