Fróðskaparrit - 31.12.2000, Síða 85

NØRINGIN HJA TOSKINUM A LANDGRUNNINUM:
GÝTINGARØKI, EGGSPJAÐING OG FØÐIN HJA LARVUNUM
89
(the pre-bloom period), these copepods
spawn mainly in the western and north-
western shelf regions and the offspring are
then advected clockwise and dispersed
onto the central shelf. Later in spring, their
spawning increases on the central shelf too
(Gaard, 2000).
The shelf ecosystem is also inhabited by
several fish stocks, which breed and grow
within the ecosystem. One of these fish
stocks is the Faroe Plateau cod. Its spawn-
ing takes place mainly from February to
May (Joensen and Táning, 1970). Peak
spawning, however, occurs in the second
half of March (Hansen et al., 1990). The
main spawning grounds are in two areas,
one to the west and one to the north of the
islands at bottom depths of about 80-150 m
(Jákupsstovu and Reinert, 1994). These
areas are close to the tidal front that sepa-
rates the shelf water from the offshore envi-
ronment. The relatively long renewal time
of the shelf water is a prerequisite for re-
taining the cod eggs and larvae within the
ecosystem. However, by spawning so close
to the front, the risk for the eggs and larvae
to drift out of the ecosystem may be con-
siderable. Hansen et al. (1994) hypothe-
sised that this risk would be especially high
during periods with strong winds. As cod
spawns in these areas despite this risk, there
may be other benefits that, in the long term,
compensate for the risk of drifting off the
shelf.
In this study, we have examined the
food-related spawning strategy of Faroe
Plateau cod by comparing spawning locali-
ties and offspring advection with produc-
tion and availability of preferred food items
for cod larvae on the Faroe Shelf during
spring.
Materials and Methods
The data presented in this paper originate
from several research cruises with the R/V
Magnus Heinason in Faroe Shelf waters
and the surrounding area. Demersal
spawning cod were collected during Febru-
ary-March 1995 and 1999; hydrographic
data, cod eggs, and young cod larvae were
collected in April 1995 and 1999; egg pro-
duction rates of Calanus finmarchicus were
measured in April 1997, 1998, and 1999;
and larger cod larvae were collected in May
1995.
In order to avoid possible effects from
diel vertical migration of the fish and
plankton and to avoid possible diel differ-
ences in spawning activity of C. finmarchi-
cus, all sampling was carried out during
daytime, between 06:30 and 18:30.
Cod abundance, size and maturity
Demersal spawning cod were collected
during the annual spring ground fish sur-
veys. One hundred fixed stations, covering
the area on the Faroe Plateau within the 500
m contour, were sampled annually, be-
tween 24 February and 21 March 1995, and
between 26 February and 20 March 1999.
The fishing gear was a box trawl (116 feet)
with a mesh size of 40 mm in the cod end.
The bridles had a length of 60 m at shallow
stations and 120 m at deep stations. The
doors were of Steinhamn Type No. 8. The
trawling time was one hour and the distance
covered was about three nautical miles.