Fróðskaparrit - 01.07.2004, Síða 82

80
MERCURY 1N LIVER, EGGS AND FEATHER OF BLACK GUILLEMOT
CEPPHUS GRYLLE FAEROENSISIN THE FAROE ISLANDS
as would be the case if the bird had changed
their diets the years the pollutants measure-
ments were ongoing towards a lower troph-
ic level. But as the stable isotopes analyses
do indicate a change in the downward di-
rection, it is speculated whether the black
guillemots these years may have changed
the diet from a migrating species towards a
local species occupying a higher trophic
level, as would be the case in going from
for example sandeel to cod. The likelihood
of the reduction in egg mercury concentra-
tion being a reflection of changing environ-
mental pollution of mercury is limited. It is
plausible that part of this decrease could be
a consequence of reduced pollution, how-
ever it is not possible to substantiate this
because the location of the source of the
mercury, which is available for these black
guillemots colonies, is not known. A simi-
lar study of stable nitrogen isotopes and
mercury in fulmars from Shetland and Out-
er Hebrides gave a similar trend where spa-
tial comparisons of mercury and 6 I5N
gave inverse relative changes and thus con-
cluded that the trophic level was not the
principal factor in determining mercury
concentration (Thompson et al., 1998).
Discussion
Spatial comparisons
As the growth of feathers offloads the
bioavailable body pool of mercury, the pro-
duction of eggs provides a route for detox-
ication in the female (Backstrom, 1969;
Lewis et al., 1993). It is questionable
whether this excretion is detectable above
excretion following the non-sexually relat-
ed processes, and studies of mercury in
adult specimens of known age of gulls,
great skuas and an albatross species have
revealed that the mercury concentration in
adults is not dependent on age nor sex (Fur-
ness et al., 1990; Thompson et al., 1991;
1993). The present study did find a differ-
ence between the adult female liver mer-
cury concentration and that in the juvenile
females, but not between the females and
males. Thus the detoxification due to
growth of eggs is not of a magnitude suffi-
cient to be detected above the variability
stemming from other elements of biologi-
cal processes and “lifestyle”. The analyses
of the present material also showed that
there were age-related differences in liver
mercury concentrations, but that the indi-
vidual variability among the males was so
great that this difference could not be de-
tected when only the males were studied.
Data for comparision is available from
Greenland, where the black guillemot egg
mercury concentration was found to be
0,34 mg/kg and 0,26 mg/kg ww in 1999
and 2000 respectively, in two different
colonies (Riget et al., 2003). Combining
the data from the two sites in the present
study gives mean egg mercury values of
0,51 and 0,33 mg/kg (calculated from data
in Tab 1), for 1999 and 2000 respectively.
Black guillemot eggs from three colonies in
Arctic Canada in 1993 and 1998 have been
shown to contain mercury in the range 0,39
mg/kg to 0,60 mg/kg (Braune et al., 2002),
and are thus in the same range as the ones
from the Faroe Islands.
The May liver mercury concentration in
black guillemots in Iceland (Gunnarsson et
al, in press), was 0,9 mg/kg, and thus sim-