Fróðskaparrit - 01.01.1987, Síða 82

86
SPAWNING OF ATLANTIC HALIBUT
tween 10 and 900 m (Table 1). The hauls la-
sted between 45 and 130 minutes and filte-
red between 2100 and 5600 m3 sea water at
the sampling depths. 5 halibut eggs were
captured. South of 61°30’N, 2 eggs were
found at 800 m depth. In the northern area,
1 and 2 halibut eggs were found at 50 and
100 m depth respectively. The latter gives
the largest egg concentration observed at
any depth with 0.48 eggs per 1000 m3 filte-
red sea water. The average diameter of the
halibut eggs was 3.22 ± 0.12 mm. Unfortu-
nately, all halibut eggs were dead and cyto-
lized after capture, such that their develop-
mental stages could not be determined.
Additional to the halibut eggs, 3 small
eggs (two with diameter less than 2.0 mm,
and one with diameter 2.7 mm, species
unknown) and 20 larger eggs with average
diameter 3.60 ± 0.08 mm, segmented yolk,
and a single yellow oil globule(average
diameter 0.97 ± 0.12 mm), were captured
during the surveys.
Discussion
Apparently, some differentiation exists in
the distribution of halibut with respect to
age/size during winter in the investigated
area. Most of the fish in deep water were
mature, while in shallower strata small,
immature fish were more abundant. This is
consistent with observations made in the
Nova Scotia/New Foundland area in North
America (McCracken 1958). Furthermore,
the almost complete absence of immature
fish below 700 m depth, which from the ap-
pearance of fish with running gonads and
pelagic eggs in the water column clearly
should be considered a spawning area for
the species, is consistent with observations
from spawning areas on the coast of Nor-
way (Devold 1938, Mathisen & Olsen
1968, Haug & Tjemsland 1986). The occur-
rence in February of some mature fish with
running gonads at depths above 700 m,
indicate that some spawning must also take
place at these depths.
The apparent sexual difference in age
distribution in the deeper strata, with a
large proportion of males being younger,
must be attributable to the lower size and
age at which the males attain sexual matu-
rity (Jákupsstovu & Haug 1987), and, thus,
recruit to the spawning stock.
Based on data from the coast of North
Norway, Olsen (1969) suggested that old
fish which had spawned in previous years
arrived on the spawning grounds earlier
than first time spawners. The present size
compostion data give no evidence for such
conclusions i the Faroe area.
Our hydrographical observations of ex-
tremely cold bottom water in the north-
most part of the protected area are consi-
stent with the fact that this is a part of the
Faroe Bank Channel which runs north-
westwards between the Faroe Plateau and
the Faroe Bank and is the deepest channel
through in the Greenland-Scotland ridge.
Trough this channel is a continuous over-
flow of cold water masses from the Norwe-
gian Sea to the North Eastern Atlantic; this
cold subsurface current then follows the
western flank of the Iceland-Faroe ridge,
westwards along the deep parts of the
southern Icelandic slope before it turns
southwards to the southwest of Iceland
(Hansen 1985). There also is some evi-
dence for another branch of this flow
descending westwards along the northern
slope of the Faroe Bank (Hansen loc. cit.),