Íslenskar landbúnaðarrannsóknir - 01.09.1978, Side 29

THE ATLANTIC SALMON IN ICELAND 27
TABLE 2.
Number of salmonid parr per 100 m2 of river bottom in several Icelandic rivers.
River Year Number of parr per 100 m2
Úlfarsá 1975 18.0-677.0
Grímsá, tributary to Hvítá 1976 0.4-57.5
Tunguá, tributary to Grímsá 1976 16.3-79.8
Langá 1975 48.0-112.0
Langá 1977 62.0-121.0
Austurá, tributary to Midfjardará 1976 5.0-17.0
Svartá, tributary to Blanda 1976 3.3-37.3
Laxá in Adaldalur 1971 40.9-108.0
Mýrarkvísl, tributary to Laxá 1971 107.0
Reykjadalsá, tributary to Laxá 1971 126.0
and gastropods. There is no information
on parr older than 2+.
Other species in the nursery areas
All the five species of freshwater fishes
native to Iceland may occur in the same
rivers. Their distribution varies in differ-
ent parts of the country. The salmon are
found in the rivers with the warmest water
during the summer. Sea trout are most
abundant in rivers in the south and south-
ern half of the west coast, in most cases in
the same ones as the salmon frequent. The
European eel are primarily found in the
rivers where sea trout are abundant. The
sea char are numerous in rivers all over
the country except in the southern and
southwestern part. The threespined
stickleback is véry common in fresh water
up to 300-400 m above sea level
(Saemundsson, 1926).
The competition between salmon and
other species in Icelandic rivers has been
studied in only two instances and a study
was once made of competition between
salmon and char in a fish pond. In other
instances references have to be made to
studies of competition between salmon
and eel on one hand and salmon and
stickleback on the other hand in rivers in
Great Britain, which can be expected to be
somewhat similar to the situation in
Icelandic rivers.
In the river Ulfarsá are found all the five
species of fish which are native to fresh
water in Iceland. Tómasson (1975) studied
the food of salmon and of brown trout
which were both feeding on the same kind
of animals. Both species are territorial in
their behavior, but they prefer different
biotopes, and they are dependent on the
velocity of current, nature of the river bed,
distance from the river banks, and depth
of water. Karlström (1972) states that
salmon are rarely found in current with a
velocity below 0.10 m/sec, and less fre-
quently below 0.50 m/sec than over. The
brown trout, on the other hand, are often
found in current velocities under 0.10
m/sec and seldom over 0.50/sec. The
larger individuals of both species are
found in swifter current than the smaller
ones. The salmon parr are found near the
bottom on coarse gravel to light shingles,
i.e., with a diameter from 2-30 cm,
whereas brown trout parr occur nearer the