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.