Fróðskaparrit - 01.07.2004, Blaðsíða 77

KYKSILVUR í LIVUR, EGGUM OG FJØÐUR
CEPPHUS GRYLLE EAEROENSIS IN THE FAROE ISLANDS
75
moult, so that the moulting becomes an im-
portant part of the detoxification of the
body pool of mercury (see for instance
Lewis and Furness, 1991), and thus feath-
ers will reflect the contamination at the site
of foraging during moult (Goede et al.,
1989).
Therefore, as a stationary species is cho-
sen as indicator species, it can be assumed
that the feather mercury concentration will
reflect the mercury load of that particular
area as long as the trophic level of the
species remains the same. Studies have re-
vealed that indications of the trophic level
of a seabird (or other species) may be
achieved via the analyses of fractionation
of stable isotopes of nitrogen in particular,
but also of carbon and sulphur (Hobson and
Welch, 1992; Hobson et al., 1994). Espe-
cially the fractionation of nitrogen isotope
l5N relative to that of l4N (denoted 6 15 N)
is supposed to provide information on the
trophic level, whereas the fractionation of
carbon isotopes (13 C/12 C, denoted 8 13 C )
is supposed to give insight into the proxim-
ity to the terrestrial environment. Typically,
a change in 3-4 %o of 8 15 N is thought to ac-
company a one tier shift in trophic status
(Peterson and Fry, 1987).
Due to the storage of birds in museums it
has been possible to elucidate historical
trends in mercury contamination through
the analyses of feathers (Thompson and
Furness, 1989; Appelquist et al., 1984) as
well as spatial trends like the study includ-
ing guillemots frorn the Baltic and the
North East Atlantic (Somer and Appel-
quist, 1974; Appelquist et al., 1985; Fur-
ness et al., 1995).
Methods
Black guillemots (142 individuals in all)
were shot using mainly steel-hail near
Sveipur and Hestoy from November 1995
to February 1997, with sampling taking
place approximately every second month.
The birds were registered and the external
measures taken on one and the same day.
The birds were stored frozen until further
treatment. During dissection, the sexual
status was recorded, for the female this sta-
tus was inferred from the appearance of the
ovary and oviduct, and for the males the
sexual status was determined from the ex-
ternal appearances among them the plum-
age and possible brood patches in combina-
tion with an assessment of the gonads. The
birds where thus sorted into age and sex
classes of adult (ie. breeding) females and
males and juveniles (pre-breeding). Body
feathers from the back and under one wing
were taken from 15 indiviđuals and analy-
sed separately for mercury. These individu-
als were taken at Hestoy in August 1996
and near Sveipur at Streymoy in June 1996.
A selection of samples from each bird were
taken into storage at -f20()C in the Environ-
mental Specimen Bank at the Food and En-
vironmental Agency, awaiting further op-
portunities for analyses and studies (see
also www.hfs.fo/enviromental_specimen.
htm).
Black guillemot eggs were sampled on
Koltur and on Skúvoy in three consecutive
years in 1999, 2000 and 2001. One egg was
taken from each nest and the santpling
would ideally be done early in the egg-lay-
ing period, which begins in early June. The
eggs were stored in refrigerator until fur-