Jökull - 01.12.1969, Side 149

that took place in the spring and early sum-
mer of 1967.
It is possible to distinguish between two
different phases of the reactions of the Nor-
wegian herring migrations to changes in tem-
perature and water masses: during the first
few years untier consideration the herring
migrations responded very closely to changes
in the boundary areas of the warin Atlantic
and cold Arctic water masses. This was especi-
ally clear off the north coast in 1962 ancl off
the northeast and east coast in 1963 and 1964.
In addition the arrival of the herring ntigra-
tion seemed to be accelerated in warm years
(early advent of the biological spring) such as
the arrival of the herring migrations in 1964
wlren the migration arrived several weeks ear-
lier at the east coast than in the colder year
of 1963. There were thus temperature depen-
dent variations of the herring distribution
within the usual nrigrational pattern. If on
the other hand the hydrograpical changes are
so drastic that large areas traditionally occupi-
ed by the herring beconre uninhabitable or
even unviable new migration routes are form-
ed as described here above. When such revolu-
tionary changes have taken place it appears
that relatively small hydrographic changes
mainly affect the herring witlrin the franre of
tlre new behaviour pattern rather than causing
reversion to the previous pattern as slrown by
the changes in nrigration of tlre Icelandic
lrerring already discussed. Thus in spite of
great variations in herring migrational pattern
a certain concervatism is also observed. Finally
it is necessary to stress the fact that the radical
changes that have taken place in stock struc-
ture and stock abundance lrave been just as
variable in many respects as the hydrographic
conditions during the years under considera-
tion.
REFERENCES
Anon. 1964: Report of the Joint Investigations
on the Distribution of Herring in Rela-
tion to Hydrography and Plankton in the
Norwegian Sea June/July 1962. Annls.
Biol. Copenh. 19, 193—198.
— 1965: Report of the Joint Investigations
on the Distribution of Herring in Rela-
tion to Hydrography and Plankton in the
Norwegian Sea, June 1963. Annls. Biol.
Copenh. 20, 246-249.
Anon. 1966: Report of the Joint Investigations
on the Distribution of Herring in Rela-
tion to Hydrography and Plankton in the
Norwegian Sea, May/June 1964. Annls.
Biol. Copenh. 21, 183—188.
— 1967: Report of the Joint Meeting on the
Distribution of Herring in Relation to
Hydrography and Plankton, Seyðisfjörður,
20.—23. June 1965. Annls. Biol. Copenh.
22, 188-195.
— 1968: Report on the Joint Meeting on
Atlanto Scandian Herring Distribution,
held at Akureyri 12.—14. June 1966.
Annls. Biol. Copenh. 23, 215-220.
Devold, F. 1968: The Formation and Disapp-
earance of a Stock Unit of Norwegian
Herring. Fisk Dir. Skr. Ser. Havunders.,
15.
Dragesund, O. 1960: Observationer over sildas
gyting i Fangenskap. Fauna 4, 137—143.
Jakobsson, J. 1962: On the Migrations of the
North Coast Herring during the Summer
Season in Recent Years with Special Re-
ference to the Increased Yielcl in 1961 and
1962. ICES C. M. Herr. Comm. Doc. No.
98.
— 1968: Icelandic Herring Investigations
1966. Annls. Biol. Copenh. 23, 124—129.
— 1968: Herring Migrations East of Iceland
during the Summer and Autumn 1966 and
1967. Fisk. Dir. Skr. Ser. Havunders., 15.
— and Östvedt, O. J. 1965: Report of the
Joint Meetings of the Norwegian and Ice-
landic Scientists Working on Board G. O.
Sars and Ægir during the First Half of
June 1961. ICES C. M. 1965. Herr. Comnr.
Doc. No. 149.
Malmberg, S. Aa. 1967: Breytingar á ástandi
sjávar milli íslands og Jan Mayen. Ægir,
60, No. 12. 219-222.
— 1969:
Stefánsson, U. 1962: North Icelanclic Waters.
Rit Fiskideildar, 3, 57.
Östvedt, O. J. 1965: The Migration of Nor-
wegian Flerring to Icelandic Waters and
the Environmental Conditions in May—
June, 1961-1964. Fisk. Dir. Skr. Ser. Hav-
unclers., 13. No. 8.
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