Íslenskar landbúnaðarrannsóknir - 01.09.1978, Side 38

36 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
occasions. The mature salmon return to
the trap at the outlet. The experiment has
had some success. Char are also found in
the lake and spawn there.
Stocking rivers
Icelandic rivers have been stocked for de-
cades with small numbers of unfed fry.
After the Ellidaár River Hatchery started
in 1932 a supply of several hundred
thousand unfed fry were on the market
annually. They were released in many riv-
ers. In the early fifties 1-summer-old fry
were available and in the sixties smolts
were on the market, al first mostly 2- and
3- yearoids. During the last decade mostly
1- and 2- year-old smolts have been used
for stocking.
The stocking of rivers with unfed fry,
1-summer-old fry, and smolts have been
plotted against the catch records for each
district (Alexandersdóttir 1975). The
study shows no obvious correlations be-
tween the releases and catches. The re-
leases of unfed fry can be expected to have
been of little value in most cases, because
of poor handling of the fry during trans-
portation and faulty methods in releasing
them. Besides, the fry were often released
in river areas, where salmon vere spawn-
ing, and competing with the natural fry
and parr. This is still true in some cases,
especially when 1-summer-olds are liber-
ated.
y\n experiment was made by the Insti-
tute of Freshwater Fisheries releasing un-
fed fry and fry fed for a few weeks in the
barren stream Fossá, a clearwater tribut-
ary to the glacial river Thjórsá, and its
tributary Raudá in the valley of Thjórsár-
dalur in southern Iceland. The release
took place on May 30,1974. The river has
been electrofished several times since
then, the last time being in September
1976. The parr have shown a normal
growth, being from 6.7-12.2 cm in length
after 3 summers in the stream. The rate of
survival is unknown.
There is little direct evidence available
for the success of releasing smolts, except
for the experiments at the Kollafjördur
Fish Farm and in the river Ellidaár and
the river Artúnsá (Isaksson, Rasch, and
Poe 1978). The releases of 1-year-old
smolts which have been reared indoors
exposed to electric lights for 24 hours a
day all winter have been a failure, as men-
tioned earlier (Gudjónsson 1973, Ísaksson
1976). A great number of artificially
reared smolts, which have been released
in Icelandic streams in the past, have re-
ceived that treatment.
Improvement in stocking
Improvement in returns of artificially-
reared salmon smolts is expected in the
future, when the smolts will be kept for
2-4 weeks in special release ponds located
on the banks of the rivers, in which smolts
are to be released and fed before they mig-
rate to the sea. The results of experiments
with this method carried out in 1975-1977
in the rivers Ellidaár and Artúnsá were
compared with direct releases in these riv-
ers, showing that two to four times as
many smolts returned as mature fish from
the ones kept in the release ponds against
those released directly in the rivers
(Ísaksson, Rasch, and Poe 1978).