Working Group on Seabird Ecology (WGSE). ICES CM 2004/C:05 ...

The pelecaniformes (cormorants, shags and gannets) seem to be more important in NAFO 4 and 5 (where they make up
20% by number and 30–45% by biomass respectively) than in any other NAFO or ICES subarea. In the eastern North
Atlantic they constitute only 5–7% by number and 16–22% by biomass in the areas compassing the North Sea and
English Channel (IVa-c, VIId,e) and the Faeroes and western UK (Vb, VIa,b,f,g,j) (Table 5.1)
Constituting 40% and 41% by number and 60% and 21% by biomass of the population, eiders and gulls respectively
dominate the seabirds breeding in the shallow, inland Baltic Sea and its approaches (ICES III). Approximately 45% of
all the ICES eiders (ca. 1 million pairs) breed in subarea III. Eiders also reach their largest proportions (10% and 15%
by number and 19% and 27% by biomass in the inshore NAFO subareas 4 (St. Lawrence and Nova Scotia) and 5 (Gulf
of Maine and Georges Bank) respectively. In these same subareas gulls constitute ca. 40% by number and 25–45% by
biomass.
The only subarea in the NAFO and ICES areas where gulls dominate the seabird breeding community is NAFO 6 (south
Maine to Virginia). Of nearly 250 000 pairs of seabirds breeding in this subarea, 70% are gulls (mainly laughing gulls
and herring gulls). They and terns make up nearly the entire community (88% and 8% of the total biomass). In the
groupings of ICES subareas used in this report, gulls make up 6–40% of the numbers and 6–36% of the biomass.
Nowhere do terns constitute > 10% of the numbers or 1% of the biomass.
In addition to the large differences in breeding populations in the W and E Atlantic, there are much larger differences
between the two regions due to huge seasonal movements of birds from the Southern Atlantic through NAFO areas than
through ICES areas. These, and large seasonal migratory movements of birds between and within ICES and NAFO
areas are described and discussed in the next section.
5.2.2 Seasonal changes in numbers and biomass of seabirds in ICES and NAFO areas
In general, the seabird community in the NAFO areas is dominated by huge numbers of individuals feeding at low
trophic levels, two of which are of small-sized planktivorous species (Wilson’s storm petrel, little auk).
Due to temporary movements of birds from the southern Atlantic into northern waters, and the migration of North
Atlantic seabirds across fishing areas, there are considerable seasonal changes in numbers and biomasses of seabirds
occupying the various parts of the North Atlantic (Tables 5.3–5.6). Such movements include those of large numbers of
birds out of the northernmost subareas (ICES I and IIb, NAFO 0 and 1) into milder subareas in autumn and winter. For
example, the large increase in NAFO 2 and 3 (E. Newfoundland and Labrador) in autumn and winter is due to millions
of eiders, auks and kittiwakes entering the areas from colonies outside the NAFO areas (in the eastern Canadian Arctic),
colonies in NAFO 0 and 1 (E. Baffin Island and W. Greenland) and in ICES IIa, IIb and Va (Barents Sea, Norwegian
Sea and Iceland). Similarly, nearly seven million seaducks winter in the Baltic Sea (ICES IIIa-d) but leave again in
spring to breed inland. These include 4.3 million long-tailed ducks, 1.2 million common scoters and 1 million velvet
scoters. In the western Atlantic, 4.5–5 million non-breeding birds (mostly great shearwaters, sooty shearwaters,
Wilson’s storm-petrels) enter the southern NAFO areas from the southern oceans in summer, and 1.5 million ring-billed
gulls move out to the coast in the same areas in winter (Table 5.7, ICES 2003).
It should be noted, however, that the quantification of the movements of seabirds across the fishing areas is based on
very poor data as very little is known about the actual numbers of the different species in the different areas at a given
time. Many of the figures used here are not more than educated guesses!
Table 5.3. Approximate numbers of seabirds (millions of individuals) occupying ICES subareas in winter, spring, summer, and
autumn.
ICES subarea Winter Spring Summer Autumn
I,IIa,IIb Barents and Norwegian Seas 15.1 22.8 26.8 27.3
Va,XIVa,b E. Greenland and Iceland 21.4 33.9 38.6 33.1
IVa-c,VIId,e North Sea and English Channel 8.9 8.3 8.8 8.8
IIIa-d Baltic, Skagerrak and Kattegat 10.2 9.8 3.9 5.8
Vb,VIa,b,f,g,j Faeroes and W. UK 10.3 12.6 13.2 13.6
VIIIa-c,IXa,X France, Iberia, Azores 1.3 2.1 1.0 1.4
Total 67.1 89.5 92.4 90.1
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ICES WGSE Report 2004