Fróðskaparrit - 31.12.2000, Page 94

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REPRODUCTION OF FAROE PLATEAU COD:
SPAWNING GROUNDS, EGG ADVECTION AND LARVAL FEEDING
spawning grounds. Inside these spawning
grounds (mainly the northern one), the po-
sitions of the densest concentrations of
spawning cod may also vary interannually.
The peak spawning time in the western
spawning area occurred at the same time of
year in 1995 and 1999 (Table 3). Even
though the material is based on data from
only one station, the large cod catches and
the high maturity status each year indicate
that the results are representative for the
whole western spawning area. The materi-
al for the northern spawning area did not al-
low direct comparison in time and location,
but indicates, nevertheless, that the peak
spawning time could be somewhat later in
1995 (two stations having average maturity
of 5.0 on March 5) compared to 1999 (5.7
and 5.9 on 13 March at the same stations).
These stations had good cod catches (be-
tween 900 and 6.100 kg) and were located
just north of the second largest island and
north of the northemmost island, respec-
tively (Fig. 2).
The in situ temperature on the Faroe
Shelf in April 1995 and 1999 (mainly be-
tween 6.5 and 7.0°C) is typical for that time
of the year (Smed, 1952; Hansen, 2000;
Heath et al, 2000b). At this temperature,
the duration from spawning to hatching for
cod eggs has been estimated to be about 12-
14 days (Iversen and Danielsen, 1984).
The average, residual anticyclonic current
at the spawning grounds is about 5-10 cm
sec'1, corresponding to about 4-9 km day'1
(Hansen, 1992; Hansen and Farsen, 1999).
Hence, the cod eggs can be expected to drift
about 50-100 km clockwise from the
spawning areas before they hatch. Thus,
eggs that are spawned in the western cod
spawning area can be expected to hatch in
the northern shelf region, while eggs that
are spawned in the northern spawning
grounds can be expected to hatch in the
north-eastern and eastern shelf regions
(Figs. 2 and 4).
Since only those cod eggs that were so
well developed that the characteristic pig-
ment pattern for cod larvae could be recog-
nised in the embryos were counted, the
eggs in Fig. 4 are estimated to represent
only the last one or two days prior to hatch-
ing. Hence, the cod eggs in Fig. 4 most
likely have been transported about 50-100
km anticyclonically from their spawning
grounds. The distribution of these eggs in
mid-April 1995 showed one abundance
maximum in the north-western and north-
em shelf regions and another on the eastern
shelf region. The question arises as to
whether or not the two patches originate
from the westem and northern cod spawn-
ing grounds, respectively. In the north-
western shelf regíon, cod eggs were distrib-
uted quite close to the salinity gradient bor-
der. This could make the eggs quite vul-
nerable to drifting off the shelf during peri-
ods of south-westerly storms, which are
quite common in the area. Further east,
they were advected closer to land. Unfor-
tunately, no samples were collected in the
southern part of the shelf that year, and,
therefore, the distribution information in
Fig. 4 does not show a complete picture.
In late April 1999, the larvae were large-
ly concentrated in the central and western
shelf areas. These larvae (and eggs) may
have been transported in an almost com-