Íslenskar landbúnaðarrannsóknir - 01.09.1978, Blaðsíða 112

110 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
escapement which was spawning above
the trap.
Eslirnalion of egg to smolt survival
If we have the wild smolt survival and the
resultant run of salmon in a year, it is
possible to calculate the-egg-to-smolt sur-
vival using the escapement a few years
earlier and the average fecundity of the
females.
The estimated survival ofwild smolts is
approximalely 26% '(Fig. 2). The total
estimated return from wild salmon as ap-
proximately 3,600 in 1976 which means
that the total outmigration of smolts in
1975 was close to 14.000. Fridriksson
(1949) showed that the majority of the
smolts at Ellidaár stay three winters in
freshwater, which means that the smolts
in question were mostly 1971 (brood). Ac-
cording to Mundy et al. (1978), the es-
capement at Ellidaár in 1971 was 1,560
salmon. Assuming a 50% female ratio,
780 females spawned in that year.
Fecundity data from grilse spawned at
Kollafjördur indicate that a female grilse
lays about 0.5 liters of approximately
8,800 eggs per liter or an average deposi-
tion of 4,400 eggs. Since the present data
indicate that the grilse at Ellidaár are
smaller than those at Kollafjördur, we will
use a figure of 4,000 eggs per female.
The total egg deposition at Ellidaár in
1971 was 780 X 4,000 = 3,120,000 eggs.
The total survival from eggs to smolts
(14,000) was thus 0.4%. This rough figure
seems to be comparable to figures re-
ported by Buck and Munro (1972) for
Girnock Burn in Scotland which
amounted to 0.5-0.7%. These figures, of
course, are low compared to the 50%
eggs-to-smolt survival obtained in hatch-
eries.
Survival of hatchery and wild smolts
The survival rates of the various hatchery
smolts including 1976 and 1977 recovery
seasons are shown in Fig. 2. The release
pönd smolts produced better survival
than that obtained from the direct plant
smolts, significant at the 0.05 level. Survi-
val was doubled by using the release pond.
This difference might be even greater
since the smolts in the direct plant were
15.5 cm long compared to 14.0 cm in the
release pond groups.
The total return from the release pond
group (8.2%) is very similar to the survi-
val of 2-year outdoor smolts released at
Kollafjördur Fish Farm in 1975 with only
one group exceeding 9% and all others
being below 6% (Isaksson and Bergman,
1978). There is no question that a consid-
erable improvement in return rates would
have been observed by using higher qual-
ity smolts. Therefore, direct plants of
smolts into rivers should be discontinued.
The release ofhandled hatchery smolts,
those tagged at the river, was primarily
intended as a control for the wild smolts. If
one compares the survival of handled and
unhandled hatchery smolts, there is ap-
proximately 24 percent difference in sur-
vival which is assumed due to the extra
handling at the river. Application of this
factor to the wild smolts increased the es-
timated survival from 20.8 to 25.8%.
The survival of the wild smolts, which
only measured 12.5 cm at downstream
migration, is exceptional compared to the
hatchery smolts; as a matter of fact, such
figures have never been obtained for At-