Fróðskaparrit - 01.01.1987, Side 84

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SPAWNING OF ATLANTIC HALIBUT
i.e., just north of the spawning area. The
extremely narrow front between this cold-
water current and the warmer (8°C) water
further south in the protected spawning
area might represent a clue for halibut to
identify the spawning area, although there
is no evidence from tagging experiments in
North Norway that halibut navigate in rela-
tion to currents when on migration (Godø
& Haug 1988). The potential deep-water
current navigation of halibut in Faroese
waters should be studied further.
The number of halibut eggs found during
our February surveys was rather low. How-
ever, according to Jákupsstovu & Haug
(1987), the sampling probably took place
before the peak in spawning and more
planktonic eggs could probably have been
expected later in the year. This is suppor-
ted by previous surveys in areas near or just
above the continental slope between the
Faroes and Iceland (Vedel-Táning 1936)
and south west of Iceland (Mclntyre 1958),
in Aril and early May, which yielded consi-
derable numbers of eggs, clearly in excess
of our present results.
The rather homogeneous hydrographical
conditions observed from the surface to
bottom south of 61°30’N, and from the sur-
face to c. 400 m depth north of 61°30’N may
have contributed to an even vertical egg
distribution, thereby lowering their relati-
ve abundance at all depths and reducing
their chances of being caught in horizontal
hauls with the type of gear/filtering capaci-
ty used. All eggs were found in temperatu-
res and salinities of respectively 8.0-8.1°C
and 35.0-35.2 %0. They were found at lar-
ge depths in the south, whereas in the
north, they were only found in the upper
layers. This apparent difference may ind-
icate an influence of physical factors upon
the vertical distribution of the eggs similar
to those seen in Norwegian fjord areas by
Haug et al. (1986). Further verification is
needed, preferably later in the year when
more abundance of planktonic eggs can be
expected to be found.
The observed egg diameters of the hali-
but eggs found is consistent with previous
measurements of pelagic halibut eggs (Ve-
del-Táning 1936, Haug et al. 1984, Kjørs-
vik et al. 1987). According to Russell
(1976) the larger eggs found which had seg-
mented yolk and a single yellow oil globule
were most probably from Argentinus silus,
a species whose planktonic eggs were
found in this area also during the previous
surveys of Vedel-Táning (1936).
Acknowledgements
Thanks are due to the crew and field assi-
stants, A. Henriksen in particular, on
board r/v »Magnus Heinason« for help du-
ring field work, B. Hansen for help with
the hydrographical recordings and con-
structive criticism, M.S. Nielsen and A.
Svendsen for technical assistance, S. Sund-
by for criticism of the manuscript and R.T.
Barrett for corrections of the English. Fi-
nancial support was received from the Nor-
wegian Council of Fisheries Research
(INFFR), project no. 1.405,003.
References
Bedford, B.C. 1983. A method for preparing sections
of large numbers of otoliths embedded in black
polyester resin. J. Cons. int. Explor. Mer 41: 4-12.
Devold, F. 1938. The North Atlantic halibut and net
fishing. Fisk Dir. Skr. Ser. Hav Unders. 5: 1-47.