Foraging gannets on the front
line
Date: September 21, 2016
Source: University of Exeter
A team of scientists led by
Plymouth University and the University of Exeter examined the feeding
behaviours of breeding northern gannets (Morus bassanus) in the Celtic Sea.
They showed that in the majority
of cases, the birds performed shallow and short dives with less swimming when
at ocean fronts, signifying the possible presence of abundant food closer to
the water's surface.
Writing in Royal Society Open
Science, researchers say the findings have important implications for
conservation because these habitats could be earmarked for designation as
marine conservation zones.
Ocean fronts occur where bodies
of water meet and are typically marked by strong gradients in temperature and
salinity, alongside converging surface current flows.
Previous studies have shown they
are important for marine ecosystem functioning, with accelerated photosynthesis
creating more plankton and thus attracting more fish, which may be concentrated
at the water's surface.
Gannets feed by flying high and
then circling before plunging into the sea to catch fish. The RSPB estimates
there are 220,000 gannet nests in the UK, and because they only breed at a few
selected sites, they are on the organisation's Amber List for conservation.
For this study, which ran over
two years, scientists tracked 53 breeding birds using bird-borne GPS devices
and time depth recorders, examining the relationship between 1,901 foraging
dives and satellite-detected ocean fronts in the Celtic Sea.
The results showed that in the
majority of cases around fronts (~94% of dives), birds deployed a short
V-shaped dive, indicating food was easier to catch close to the surface. In
some instances, where food is less easily available, gannets may use a U-shaped
dive, spending more time underwater so as to reach food at deeper depths, but
this rarely occurred in frontal dives (~6% of the time).
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