Seabird 2000
European Shag Phalacrocorax
aristotelis
Maps and Figures
The following was adapted from original text by Sarah
Wanless and Mike P. Harris in
Seabird Populations of Britain and Ireland (with
permission from A&C Black, London).
The European Shag is endemic to the northeast Atlantic and the
Mediterranean. An inshore species that is almost never observed out
of sight of land, it takes a wide range of small fish that it
catches on or near the seabed over both sandy and rocky substrates.
Shags nest on offshore islands or on cliffs and colonies range in
size from a few to several thousand pairs. Numbers in Britain and
Ireland increased substantially during the 20th century
until the SCR Census in 1985-88, but have subsequently declined in
most parts of Britain and Ireland.
European Shags build large conspicuous nests and the count
unit during Seabird 2000 was the apparently occupied nest (AON).
These nests superficially appear straightforward to count, but
there are, however, several major problems associated with a
widespread survey of this species: i) detection of nests - these
can be hidden among boulders and in caves, or can easily be
overlooked when present at low densities among other species in
large cliff nesting colonies; ii) a prolonged and variable breeding
season - in Britain eggs have been laid in every month of the year
except September and October; iii) occasional years when many
adults do not breed - however, such events tend to be localised and
did not appear to be a problem during the census. Seabird 2000,
aimed to overcome the second problem by conducting a single count
in the period of maximum nest occupancy (1 May-25 June). However,
while previous censuses probably suffered from similar problems,
these will all lead to the underestimation of the absolute size of
the breeding population.