Íslenskar landbúnaðarrannsóknir - 01.09.1978, Blaðsíða 34

32 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
and northeastern Iceland are one year
older than indicated.
Previous age analysis of 1,026 salmon
scales by Fridriksson (1940) collected in
1938 and 1939 from fish from four rivers
are listed in Table 4. The age of 1,149 fish
from five rivers was determined from scale
samples collected from 1911—1914 and
analyzed by Dahl (Saemundsson 1913 and
1917) (Table 5). Fridriksson’s readings
indicated that the smolts were younger on
the average than in the more recent study
discussed above, while Dahl’s results gave
generally older smolts, i.e., 29.2—53.1 % of
the smolts were 4-year-olds.
Age. al maturity
Most of the salmon in Iceland spend 1-2
years in the sea, and a few 3 years (Table
3). Scale readings of 1,799 salmon from 10
rivers from various parts of the country
showed that 52.9% of the fish were grilse,
46.6% had spent 2 years in the sea, and
0.5% 3 years. The ratio between 1- and
2-year-olds varies between rivers. The
causes of the variations may be several,
among which are the changeable strength
of individual year classes, and the rep-
resentativeness of the samples.
In the river Ellidaár in the southwest
65.0% were grilse but only 31.9% in Laxá
in Kjós which is about 30 km further to the
north. The three main tributaries to the
river Hvítá in Borgarfjördur had
50.0-59.7% grilse; of these the
neighbouring Thverá and Nordurá had
59.7 and 59.4% respectively. In the west-
ern part of northern Iceland the
neighbouring rivers Midfjardará and
Vídidalsá had 35.6 and 51.8% grilse, re-
spectively. Laxá in Adaldalur in the east-
ern part of northern Iceland had 36.6%
grilse and a few salmon that had spent 3
years in the sea. In the ölfusá—Hvítá in
the south there were 63.6% grilse and also
a few 3-year fish. In the Sog, the tributary
which joins the river Hvítá to form ölfusá,
there were 59.1% grilse and 3.0% 3-year
fish.
When comparing the results of the age
analysis of mature salmon discussed
above with those of Fridriksson and Dahl
(Tables 4 and 5) they showed a percen-
tage of grilse in the river Elldiaár much
higher, i.e., 88.0 and 85.2, respectively,
than seen in recent age analysis. The same
was true in the river Nordurá, where Dahl
determined 74.3% grilse against 59.4% in
recent years. In the river Laxá in Adal-
dalur, Dahl’s and recent readings are ab-
out the same for the 2-year-olds in the sea;
Dahl, however, had fewer grilse, 22.1%
against 36.8%, but many more 3-year-
olds, 16.8% against 0.8%. The available
figures for the river ölfusá are not com-
parable, because the salmon migrating
through it consist of several stocks from
various parts of the big river system. Also,
61.7% of the salmon of Ölfusá-Hvítá,
from which the scale samples were col-
lected 1946—1965 (Table 3), were netted
and the rest were caught by rod and line,
while all the older scale samples (Tables 4
and 5) were had from netted fish. It might
be noted that in the Sog, which has its own
stock, all the scale samples were taken
from rod-caught fish.
Previous spawners
In tables 3, 4, and 5 are listed the percen-
tages of salmon with previous spawning
marks on their scales. These fish had thus
entered the rivers to spawn a second,
third, or even fourth time when caught.