Fróðskaparrit - 31.12.2000, Blaðsíða 97

NØRINGIN HIA TOSKINUM A LANDGRUNNINUM:
GÝTINGARØKI, EGGSPJAÐING OG FØÐIN HJA LARVUNUM
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Hence, in most years, significant egg pro-
duction of C. finmarchicus occurs during
early spring in the western and north-west-
ern shelf regions, which is markedly earlier
than in the central shelf region.
Faroe Plateau cod seem to select their
spawning grounds close to the main spawn-
ing areas of C.finmarchicus. At the time of
year when most first-feeding cod larvae oc-
cur on the Faroe Shelf (April), reproduction
of most of the neritic copepods is still at a
low level (Gaard, 1999). However, over-
wintered C. finmarchicus that have ascend-
ed from diapause in deep water (Heath and
Jónasdóttir, 1999; Gaard and Hansen,
2000) may have some significant spawning
at this early time of the year. This spawn-
ing is mainly in the western and north-
western shelf areas (Fig. 6; Gaard, 2000),
which are also the areas that are assumed to
be a major inflow area of C. fmmarchicus
onto the shelf during spring (Gaard and
Hansen, 2000). Thus, taking into account
the low reproduction of neritic copepods on
the shelf at this early time of the year
(Gaard, 1999), spawning of the overwin-
tered C. finmarchicus would, in most years,
be the most reliable food source for cod lar-
vae. By spawning in these areas, cod en-
sure that their eggs drift together with
spawning C. finmarchicus clockwise, first
to the west and north of the islands, and
then disperse onto the central shelf area.
This hypothesis is supported by the gut
contents (Table 4), where copepod eggs
(presumably mainly C. fimmarchicus eggs)
were the most important food items for
first-feeding cod larvae.
By spawning in areas close to the tidal
front, cod expose their eggs to considerable
risk of drifting off the shelf. The dominant
wind force in the area is from the south-
west (Gaard and Hansen, 2000). During
stormy periods, the risk of drifting off the
shelf to the north of the Faroes may be con-
siderable for cod eggs (Hansen et al. 1994).
Because the cod spawn in these areas, de-
spite this risk, the food-related benefits
may, in the long run, outweigh the possibil-
ity of drifting off the shelf.
In late spring, when cod larvae select
larger prey (mainly small copepodite
stages), they are dispersed inside the shelf
region and can prey on the neritic species,
which by that time in most years have start-
ed their reproduction.
Based on what is presented above, good
feeding conditions for Faroe Plateau cod
larvae would require a high level of repro-
duction of C. finmarchicus close to cod
spawning grounds during the early spring,
and then high copepod reproduction on the
shelf during late spring and summer. Some
advection of overwintered C. fimmarchicus,
together with some pre-bloom egg produc-
tion of C. finmarchicus close to the cod
spawning grounds, therefore, seem to be
the prerequisites for successful feeding
conditions for first-feeding larvae. On the
other hand, Gaard et al. (1998) suggests
that too high an advection of overwintered
C. finmarchicus onto the shelf during early
spring most likely would have an inhibitory
effect on phytoplankton production on the
Faroe Shelf. This could potentially nega-
tively affect copepod fecundity on the shelf
during spring. If this holds true, the best
feeding conditions for Faroe Plateau cod