Opportunistic sightings of killer whales from Scottish pelagic trawlers fishing for mackerel and herring off North Scotland (UK) between 2000 and 2006

Killer whale (Orcinus orca) encounters from commercial pelagic trawlers as well as other types of vessels have been documented in several regions of the northeast Atlantic; however, very little published information is available regarding such encounters in mackerel (Scomber scombrus) and herring (Clupea harengus) fisheries, in the waters between northern Scotland and Norway. Mackerel and herring are the two main fish species targeted by the Scottish pelagic fleet, primarily during October to March and June to September, respectively. Encounters with killer whales were recorded during January and February 2006 by observers on a pelagic trawler fishing for mackerel in this area. These recent data, along with historical records collected since 2000, demonstrate the existence of frequent encounters between commercial pelagic trawlers and killer whales. We describe the foraging behaviour displayed by the whales during fishing operations. Killer whales approached the vessels during retrieval of the net, and remained there until this was completed. They were sometimes sighted during steaming and towing, although there was no observed contact with the boat or net at these times. There is no evidence that the presence of killer whales reduced the amount of fish caught by the trawlers or that killer whales ever become entangled in the nets. We suggest that, during the mackerel fishing season, the whales may obtain a significant proportion of their daily energy requirements from this source.