Fróðskaparrit - 01.01.1987, Page 76

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SPAWNING OF ATLANTIC HALIBUT
61°30’N) of the spawning area. A more de-
tailed description of the Tucker trawl used
is given by Hopkins et al. (1982). Due to
the large depths involved and weather con-
ditions the opening/closing mechanism
could not be used and the trawl had to be
lowered and raised open. The approximate
volume filtered at the determined depth
during each haul (2800 m3 per hour) was
calculated using the area of the trawl op-
ening (1 m2) and the cruising speed of the
ship (1.5 knots).
Halibut eggs were identified by their dia-
meters and morphology (Russell 1976)
immediately upon arrival on deck. They
were then fixed in a solution of 2.5%
glutaraldehyde and 2.5% formaldehyde in
0.05 mol/1 cacodylate buffer (ph = 7.2, 350
mosmol/kg), for later determination of egg
diameters, and, if possible, developmental
stages according to Rollefsen (1934) and
Lønning et al. (1982).
Hydrographical data were recorded in
the centre of the two eggsurvey areas using
a Neil-Brown CTD-profiler connected to a
Hewlett-Packard computer. During the
1987 bottom trawl surveys, bottom
temperatures were also recorded at 20
minute intervals using a temperature sen-
sor mounted on to the trawl.
RESULTS
Size composition
Fish caught in the depths shallower than
700 m were generally smaller than those ta-
ken in deeper waters (Fig. 3). In the shallo-
wer depths, males seldom exceeded 100-
110 cm in length, while in the deeper areas
the length range of males was 50-180 cm.
Females were generally larger than males,
and individuals ranging in size from 50 to
Fig. 4. Age composition (% frequency) of male and femaie halibut caught above (stipled line) and below (solid line)
700 m depth southwest of the Faroes in 1983-1987. N— and N+ are number of fish caught above and below 700 m
depth respectively.