Fróðskaparrit - 01.07.2004, Blaðsíða 97

KYKSILVUR í FØROYUM - EIN GJØGNUMGONGD AV TØKUM DÁTUM
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cury than the larger (and older) ones. This
is in line with the well-known potential for
bioaccumulation of mercury. One may also
note that the concentrations of mercury in
trout from the two freshwaters Leitisvatn
(=Sørvágsvatn) and Fjallavatn are very
similar, and these waters are also close in
geographical terms situated on the island
Vágar.
Overall, the mercury concentrations in
trout were higher than in the Arctic char. It
is also seen that the mercury concentration
in Arctic char from Leynavatni is higher
than in the Heygardalsvatni, even though
the ones from Leynavatni were smaller in
both weight and length. Of importance to
note in this case is that the average age of
the two groups of char is about the same,
where Arctic char from Leynavatni had an
average age of 7,8 years while the average
age for char from Heygardalsvatni was 8,0
years. There was however, a dramatic dif-
ference in size-at-age between these two
populations stemming from on the one side
the fact that the físh in Heygardalsvatn feed
on manmade feed because there was smolt
rearing in this basin, and on the other, that
the Leynavatn char population is what is
usually termed a dwarf morph (Gydemo,
1983).
The mercury concentration in Arctic
char from á Mýrunum in 2000 is at a simi-
lar level as in Arctic char from Leynavatni,
whereas the 2001 data á Mýrunum seem
somewhat elevated. This may be interannu-
al variability stemming from what may be
termed natural variations in food availabil-
ity, or it may result from differences in wa-
ter body regulations. At present there are
not many waters with Arctic char in the
Faroe Islands, so it is not possibly to com-
pletely avoid waters with watersheds dis-
turbed to some extent by human activities.
It is believe however, that á Mýrunum is the
best choice for Arctic char sampling, be-
cause the damming here was done relative-
ly early in the hydro electrical development
history of the Faroes, and hence the erosion
at the shoreline is as low as it can be under
the circumstances. In addition to mercury
analyses, the Arctic char from á Mýrunum
wasi also analysed for selenium. Average
selenium concentration for the 2000 sam-
ples was 1,4 mg/kg, while the selenium
concentration in 2001 was between 1,76 -
2,26 mg/kg (Olsen et al., 2003).
Compared to lakes in Arctic Canada,
where the majority of lakes have Artic char
mercury levels less than 0,2 mg/kg (Lock-
hart et ai, 2001), the mercury concentra-
tion in the á Mýranar lake is high. It is also
high compared to the results of a study of
brown trout and Arctic char from high
mountain lakes in Europe and the Svalbard
Archipelago, where the mean mercury con-
centrations varied between 0,021 and 0,179
mg/kg (Rognerud et al., 2002). In Lake
Thingvallavatn, Iceland, the mercury con-
centration in Arctic char is approx. a tenth
of the level in the Faroese lakes (Jonsson,
1995). However, in certain lakes in west
and southwestern Greenland the average
mercury concentration in Arctic char is two
to three-fold higher than in the Faroes
(Riget et al., 2000). Overall thus, it may be
stated that the mercury concentration in
Arctic char in the Faroes is elevated above
the common level in many places.