Íslenskar landbúnaðarrannsóknir - 01.09.1978, Blaðsíða 31

THE ATLANTIC SALMON IN ICELAND 29
bottom with coarser material than salmon
parr do. Besides, the brown trout parr are
found on shallower water and closer to the
river banks than the salmon parr, and feed
more on terrestrial animals in the drift
than salmon parr do. Tómasson (1975)
and Karlström (1971) found this to be
true in the river Ulfarsá and river Laxá in
Adaldalur.
Egglishaw (1970), who studied pro-
duction of salmon and trout in the Shel-
ligan Burn in Scotland, states that the
stream would presumably produce more
salmon if the trout were eliminated, but
not as much as its present total yield of
salmon smolts and trout, because 30% of
the trout food is of terrestrial origin.
Power (1973) found a different dis-
tribution pattern of salmonid species in
small streams in northern Norway. He
maintains that the char occupied „head-
waters and cold streams, trout warmer
tributaries and downstream parts of rivers
too small for salmon,and salmon the lower
reaches of rivers.“ The char fry emerged
earliest and had a slight advantage in size
over 0+ parr of salmon and trout. This
pattern of distribution might also exist in
Iceland in similar rivers.
An experiment was carried out in 1976
in a Californian standard raceway at the
Kollafjördur Fish Farm to study competi-
tion between salmon and Arctic char fry in
a pond environment (Alexandersdóttir
1978). A control was run in another race-
way with salmon fry only. The bottom of
the raceways was about 2lz mud and V3
gravel. The experiment was started in
June and ended in September. The sal-
mon fry concentrated in the gravel area,
whereas the char fry were evenly distri-
buted throughout the raceway. No food
was given. The char grew fastest and had
less mortality than the salmon. The in-
stantaneous rate of growth of the char fry
was 6.59, of the salmon fry 0.19, and of the
control group 2.35. At the close of the
experiment the average length of the char
was 6.6. cm, the salmon 4.5 cm, and the
control group 5.6 cm. The salmon fry had
been fed before the experiment conr-
menced.
Thomas (1962) studied the feeding
habits of salmon, trout, and eel in the
River Teify in western Wales. He found
that there is a close resemblance between
the dietary habits ofsalmon and trout parr
of the same age, but an appreciable differ-
ence between the diet of the eel and the
other species. Sinha and Jones (1975) also
have studied the food of eel, salmon, and
trout in western Wales. They maintain
that the eel have ,,in general, much the
same diet as salmonids and must be re-
garded as competitors for available food.“
The eel can thus be expected to compete
with salmon for food in the rivers in south-
ern and western Iceland, where they are
found mainly.
Maitland (1965) studied the feeding
habits of threespined stickleback and
other species in the River Endrick in
Scotland. He found that the diet of the
threespined stickleback overlapped to a
significant degree with that of the other
species studied, among them salmon and
trout fry.
Capacity of the nursery areas
Fort and Brayshaw (1961) state that
young fish in the river require „maximum
wetted perimeter. The lower the flow in
the river the less food and the less cover is
there for them.“ Hynes (1972) states that