Fróðskaparrit - 01.07.2004, Side 119

KYKSILVUR í FØROYUM - EIN GJØGNUMGONGD AV TØKUM DÁTUM
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Species Hg, mean (range) Reference
Black guillemot, 10 eggs, Koltur, 1999 0,51 (0,35-0,97) Olsen et al., 2003
Black guillemot, 8 eggs, Skúvoy, 1999 0,51 (0,39-0,73)
Black guillemot, 10 eggs, Koltur, 2000 0,36 (0,16-0,55)
Black guillemot, 9 eggs, Skúvoy, 2000 0,30 (0,14-0,42)
Black guillemot, 10 eggs, Koltur, 2001 0,32 (0,18-0,45)
Black guillemot, 10 eggs, Skúvoy, 2001 0,33 (0,19-0,44)
Northem Fulmar, 3 eggs, 1972 0,21 (0,17-0,26)' Bloch et al., 1987
Put'fin, 1 egg, 1972 0.45 Bloch et al, 1987
Great skua, 3 eggs, 1972 1,35 (0,95- 1,59)1 Bloch etal., 1987
Great skua, 8 eggs, Saksun, 1977 1,0(0,68- 1,4) Bloch et ai, 1987
Great skua, 5 eggs, Skúvoy, 1977 1,2 (0,92-1,7) Bloch et ai, 1987
Great skua, 6 eggs, Svínoy, 1977 0,9 (0,63 - 1,2) Bloch etal., 1987
Larus fuscus, 1 egg, 1972 0,44 Bloch etal., 1987
Common guillemot, 5 eggs, 1972 0,20 Dyck and Kraul, 1984
1: The concentration of methylated mercury is available in the ref. Numbers in parentheses are minimum and maximum values.
(Olsen et al., 2003). However, paralleling
this decrease in mercury was also a de-
crease in PCB, and this is interpreted as an
indication that the reason for the decrease
may not be that the ambient level of these
pollutants has decreased, but rather that the
birds have a decreasing intake of “typical”
mercury and PCB carriers. Therefore as
part of a BSc study black guillemot eggs
samples from the Environmental Specimen
Bank were analysed for stable isotopes of
nitrogen and carbon to study whether the
observed decrease in PCB was accompa-
nied by a decrease in trophic position and
thus could stem from interannual variations
in diet (Ólafsdóttir, 2002). The results indi-
cated that there had not been any shift to
lower trophic level feeding accompanying
the decreasing pollutant concentrations. It
is nonetheless “suspicious” that both mer-
cury and PCB decrease to such extents and
other explanations are sought which may
sustain such change. Hence it is speculated
whether the black guillemots these years
may have changed the diet from a more
lipid rich fish species towards a leaner and
thus less polluted kind.
The mercury concentration in great skua
eggs are twice as high or more than the con-
centration in black guillemot eggs (Table
14), a fínding which is most likely related
to a higher intake of mercury with prey in
the predators great skuas than in the lower
tier feeding black guillemot. It is also noted
that the mercury concentration in black
guillemot eggs are higher than in the guille-
mot sp. eggs sampled in 1972 (Dyck and
Kraul, 1984). This may not be an indication
of a trend though, as the study of black and
common guillemot feathers in early seven-
ties (Appelquist et al., 1985) showed a
100% higher feather mercury concentra-
tion in the former species. Analyses of mer-
cury in black guillemots eggs in Greenland