Fróðskaparrit - 01.07.2004, Síða 111

KYKSILVUR í FØROYUM - EIN GJØGNUMGONGD AV TØKUM DÁTUM
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mius brosme). This monitoring of mercury
in físh for export was discontinued in the
early nineties and in the mid nineties envi-
ronmental monitoring on a wider selection
of species was begun. In Table 11 a broad
presentation of the mercury concentrations
measured in Faroese marine fish species
since 1993 is given. The highest concentra-
tion of mercury in fish is found in orange
roughly and tuna muscle and in sculpin liv-
er. Comparing the results of long rough dab
in Table 10 with those for the same species
taken at Norðurhavinum at 66° 01'N and
11° 54'W (Stange etal., 1996), where mer-
cury in muscle was found to be 0,02 mg/kg,
and cadmium in liver was 0,27 mg/kg, it is
apparent that the metal concentrations in
the fish from the Faroese shelf area are
somewhat higher.
A selection of the mercury data from the
monitoring of fish for export has been in-
cluded in Fig. 8 and in Fig. 9. In the Fig. 8
the results for a selection of these results
are given. The selection was done so as to
include only mercury results for a given in-
terval of fillet lengths, so that for cod and
saithe results for fillets in the interval 40 cm
to 80 cm were included, and for ling results
for fillets between 60 cm and 120 cm are in-
cluded. The analyses were done on salted
or fresh fillets, and when fresh fillets were
analysed, the reported value has been mul-
tiplied by two thus to be comparable to salt
fish measurements where the salting is as-
sumed to have led to a mass reduction of
50%. The actual mass reduction due to wa-
ter loss during salting and subsequent dry-
ing is variable, depending on the actual
quality produced (Hoydal, 1954). The wa-
ter content in the various qualities varied
from an average 32% to 48%, whereas that
of the fresh fish will be close to 80%
(Gregersen, 2001). Thus assuming a 50%
weight reduction may be an underestima-
tion of the actual weight loss due to evapo-
ration, but on the other hand does allow for
the weight of salt, which in a salted cod
may account for 16-18% (Hoydal, 1854).
The full length of the cod represented in
the 40-80 cm fillet range can be approx. 60
cm to 120 cm, when assuming the fillet
length is approx 2/3 of the fork length. This
is a quite wide range compared to the fish
included in the monitoring since 1994. In
the eighties, cod of all sized were analysed,
whereas when the purpose of the monitor-
ing during the nineties changed to become
a more general watch-keeping on the ambi-
ent pollution, a smaller fish size have been
used for analyses. This selection of moni-
toring size have been done with reference
to the monitoring guidelines of the JAMP,
and generally speaking this cod for moni-
toring use is younger (2-3 years of age) and
smaller than the fish taken for consumption
(JAMP Guidelines 1999). Thus, the results
of the earlier monitoring should be com-
pared to cod of the larger size in Table 11,
and then with the salt fish presentation of
data in Fig. 8 in mind; meaning that values
in the fígure must be divided by two to be
comparable to those in the table.
The overall level of mercury in cod in
Fig. 8, especially in the first part of the
graph, is high compared to those in Table
11 and apart from the obvious skewness in-
corporated when comparing salt fish-ww
data to fresh fish-ww data, part of the ex-