Jökull - 01.12.1969, Blaðsíða 144

ing shoals had been located in deep water
(probably ab. 200 m) where the sea temperature
was less than 0° C (Anon. 1968). In the report
it is also stressed that the conventional herring
areas off the north and northeast coast of Ice-
land, i.e. the southwest border of the cold
tongue, were almost completely devoicl of anv
C. finmarchicus concentrations. Feeding condi-
tions were on the other hand so good in the
area S of Jan Mayen and during tlie late
summer also off the east coast of Iceland that
the summer weight increase ol' the herring was
twice as high as in any one of the previous
10 years (Jaliobsson 1968). The distribution of
the herring food especially C. finmarchicus
seems to contribute to the new tendency of
the herring migrations which began in 1965,
to follow the eastern border of the tongue of
cold water northwards insteacl of migrating
against the direction of the current along the
southwest border of the cold tongue in a
northwesterly direction. The Icelandic summer
anc.1 autumn catch in 1966 was 706,000 tons of
which 98% were Norwegian herring.
1967
In the spririg 1967 the southern border of
the drift ice was only 20—40 n.m. off the
north coast of Iceland and the iceborder ex-
tended further to the east than in the pre-
ceeding years with the exception of 1965.
This year the main westward migration of
the Norwegian lierring arrived at the eastern
boundary of the tongue of cold water a little
further north than in previous years.This prob-
ably was one of the reasons why practically no
herring remained in the area off East-Iceland
as in 1966, i.e. at the southern bounclary of the
tongue of cold water, during the summer of
1967. Instead almost the entire migrations
turned northwards along the eastern boundary
of the cold water ancl by 20th of June the
herring had arrived in the Jan Mayen area.
Then an interesting thing happened: a large
proportion of the herring migration was ob-
served to turn off the main NNE migrational
route in a westerly and southwesterly direction.
This lasted, liowever, only for a week or so,
the herring soon met the very cold polar water
(less tlran — 1° C) ancl turned again in NNE
direction following some 200 n.m. behind the
140 JÖKULL 19. ÁR
other component of the migration that had
continued their NNE course without interrup-
tion. Thus the herring did not remain in the
Jan Mayen area as in 1965 and 1966 but
migrated all the way to the Bear Island-Spits-
bergen area where they remained throughout
the summer. In September and October the
herring retracted their 800 n. m. route ancl
reached the overwintering grounds east off Ice-
land at the end of October. In order to make
an attempt to understand the drastic changes
in the migrational pattern of the Norwegian
herring that took place during the spring and
early summer of 1967 it is probably not
enough to consider them in relation to changes
in sea temperature and other hydrographic
features. In addition to these environmental
changes one must also take into account im-
portant structural changes of the stock itself
which took place in the autumn of 1986. It
has aiready been mentioned that during the
late summer 1962 large concentrations of three
year old Norwegian herring (i.e. 1959 yearclass)
invaded the herring fishing areas off north
and east Iceland. This immature and recruit-
ing component of the 1959 yearclass became
an integrated part of the older herring con-
centrations in this area. Another component
of the 1959 yearclass did, however, not migrate
westwards towards Iceland but stayecl during the
prespawning phase in the Bear Island-Spits-
bergen ancl Barents Sea area. When these herr-
ing enterecl the spawning phase ot their life
cycle during the period 1963-1965 they clicl not
appear to mix with the main adult population
of the Norwegian herring which hacl their
main spawning grounds off the west coast of
Norway (off Möre). Instead separate spawning
grounds off the Lofoten islands deveioped.
Thus there were two separate spawning areas
during the period 1963—1966 and indeed there
appearecl to be two separate stock units in the
Norwegian herring in this periocl (Devold
1968, Jakobsson 1968).
During the summer 1966 there is, however,
evidence from Icelandic tagging experiments
(Jakobsson 1968) tliat some of the “western”
component feeding in the Jan Mayen area
migrated further north east ancl mixed with
the “eastern” component in the feeding areas
off Bear Island and Spitsbergen. Whether it