Fróðskaparrit - 01.01.2005, Síða 103

MERKINGARROYNDIR VIÐ FØROYSKUM TOSKI 1952-1965
101
tion (a result of the migration pattern) of
predators and preys is affecting the struc-
ture and trophic importance of food webs
(Steingrund and Gaard, 2005). In fisher-
ies management, the migration pattern of
commercial fish stocks is often used as a
guideline when defining management ar-
eas and management units, for example
in the Baltic sea (Bagge and Steffensen,
1989). When protecting local fish popula-
tions by defining areas closed for fishing
(temporarily or permanently), it is crucial
to have sufficient information about the
migration pattern of the fish populations in
question. There are several closed areas in
Faroese waters (ICES, 2004).
During its life the cod normally occu-
pies several different areas and habitats.
The larvae normally drift with the current
from the spawning area to the nursery area
for fry or juvenile fish. The juvenile fish
migrate to the feeding grounds of adult
fish when they are large enough. When
sexually mature the adult cod migrate to
the spawning area in spring and return to
the feeding area after spawning. Some
Canadian cod stocks occupy an overwin-
tering area after the feeding season in
summer/autumn and the spawning season
m spring (Chouinard and Swain, 2005).
Some populations of cod may not occupy
a]l these three (or four) different areas,
smce the nursery area sometimes is the
more or less the same as the feeding area,
as is the case in e.g. the Barents Sea (Ot-
tersen and Sundby, 2005). The feeding
area may also be more or less the same
as the spawning area (e.g. close to the
spawning area “Norðhavið” on the Faroe
Plateau, unpubl.). Some cod stocks occu-
py the same area regardless of individual
size or season, e.g. on the Faroe Bank
(unpubl.).
The migration pattern of cod may not
be constant versus time. Nursery areas
may change as observed in the North Sea
where the German Bight gradually lost its
importance as nursery area for juvenile
cod (age 1) from 1971-2002 (Blanchard
et al., 2005). Spawning areas may also
change as observed for West Greenland
offshore cod (Wieland and Storr-Paulsen,
2005) and Arcto-Norwegian cod (Ottersen
and Sundby, 2005). Feeding areas may
also change as observed for West Green-
land offshore cod in 1989-1991 that moved
to East Greenland waters (Wieland and
Storr-Paulsen, 2005). On a broad scale,
the migration pattern seems to be more
robust for north-east Atlantic cod stocks
compared to the north-west Atlantic (Ro-
bichaud and Rose, 2004).
On a broad scale, the migration pat-
tern of cod groups may be grouped into
four: sedentary, accurate homers, inac-
curate homers and dispersers (Robichaud
and Rose, 2004). Sedentary groups had
lower biomass than the others confirming
that migration/dispersal begets abundance
(Robichaud and Rose, 2004). The authors
also hypothesised that the migration pat-
tern was dependent on hydrographic con-
ditions (“oceanographic regimes”). In
the north-east Atlantic the environment
is characterised by predictable oceano-
graphic conditions leading to fairly stable
migration patterns whereas the opposite is
the case in the north-west Atlantic. Cod on