188 | Chapter 10
Conversely birds long ago learnt that fishing vessels were a source
of fish. These fish are easily snatched; perhaps they have been discarded
dead overboard or are wriggling wounded out of a trawl. Or perhaps it
is the offal, the waste after the fish are gutted, that is the attraction.
Certainly it is no surprise that seabirds are attracted to fishing vessels
and ‘free’ food. What is surprising is the distance at which birds detect
and then approach fishing vessels. When researchers examined changes
in the flight direction of GPS- tracked Wandering Albatrosses in re-
sponse to the toothfish fishing fleet operating around Iles Crozet, itself
monitored via GPS- based vessel surveillance systems, they found in-
creases in feeding behaviour only when the albatrosses were within 3 km
of boats. But the albatrosses displayed clear changes in flight direction,
towards vessels, at distances up to 30 km, a distance close to the theoret-
ical maximum visual range of an albatross.*13
Comparable long- distance detection of fishing vessels is achieved by
Northern Gannets in the Irish Sea. They are more likely to switch from
commuting to foraging when within 11 km of a fishing vessel. The Uni-
versity of Exeter researchers found the gannets had remarkable addi-
tional abilities.^14 When the vessels visible to the gannets were travelling
at fishing speeds, the birds were more likely to switch to foraging, and
less likely to switch to commuting, when the vessels were trawlers as
opposed to non- trawlers. Further, the gannets were more likely to switch
to commuting when trawlers were steaming than when they were fish-
ing. So the gannets could distinguish different types of vessel, and con-
centrate foraging at the vessel type, trawlers, where discarded fish were
more likely, and they could discern whether the trawler was actively
fishing, and likely to be a source of fish, or steaming and probably not
worth pursuing.
Attractive as fishing vessels are, they also pose risks to birds. Birds
can become entangled with nets and drown, or collide with trawl warps.
Across the world’s seas, longlines pose a fearful hazard. Sometimes tens
of kilometres in length, the lines are baited with hundreds or thou-
sands of hooks. They may be set in mid- water, often for tuna, or near
- (^) This theoretical maximum range takes account of the curvature of the earth, the height of a
fishing vessel, and the likely height above the sea of a Wandering Albatross.