Íslenskar landbúnaðarrannsóknir - 01.09.1978, Blaðsíða 103

AN EVALUATION OF SMOLT RELEASES 101
those cold streams, a release of smolts
would have to be made every year.
The most common way of releasing
smolts in Iceland has been to release them
directly into the river system from the
transportation truck. It has been sus-
pected that this release method is bad for
the smolts, since they do not get a chance
to recover after transportation and might
not stay long enough in t-he stream to get
an imprint, which is necessary for their
return. As an alternative, it has been
suggested that feeding for a period of 2-4
weeks before release in a release pond on
the river bank would enhance survival
and reduce straying. In the following ex-
periments, the release pond method and
the direct plant method were tested, both
in a productive salmon river and a barren
stream without salmon. In addition, some
2.000 wild smolts were fyke-netted from
the productive stream in order to derive
an estimate of the natural production of
smolts in the river, as well as the smolt-to-
adult survival.
RELEASE OF SMOLTS INTO A
NONPRODUCTIVE STREAM
Descriþtion of the stream
Artúnsá is located about 30 km north of
Reykjavik and about 10 km from the
Kollafjördur Fish Farm. The stream
originates in a valley which cuts into the
west side of Mt. Esja. The stream is very
short, with only 3 km from the estuary to
an impassable waterfall in the foothills of
Mt. Esja. The lower half of the stream is
flat with many good fishing holes. The
upper half is steep with many big boulders
in the streambed and few holes in which
salmon can live (Fig. 1). The water flow,
witch is variable (averaging about 0,5 m3/
sec, is almost entirely dependent on
snowmelt and rainfall. When it rains, the
stream discharge increases very quickly
and moves gravel and rocks in the
streambed. During dry spells the river can
become just a trickle. The water temp-
eratures are cold, varying with the am-
bient air temperatures. On very warm
days in the summer it may reach 10°C, but
is usually 6-8°C.
The estuary is very similar to the es-
tuary of the Kollafjördur Fish Farm. On
low tide, the salmon meet with difliculties
in entering the stream; most of the salmon
enter on high tide. This certainly is not a
problem of major concern, judging from
the experience at the Fish Farm.
Tagging and release
In the spring of 1975, a release pond was
built about 200 m from the estuary of Ar-
túnsá. The pond was excavated in the
riverbed at a convenient location where
water from the river could be piped in
without major danger of the pond being
flooded during rain. The pond could not
be drained, making it difíicult to force the
smolts out into the river at the time of
release. The outmigration thus was a vol-
untary one.
The smolts used in this experiment
were microtagged at.the Kollafjördur Fish
Farm during the first week of May. In
total, 6.000 smolts were tagged, two lots,
each with 2.000 for the release pond, and
2.000 for thedirect plant (Table 1). Repli-
cation was possible only with the smolts
kept in the release pond, due to shortage of
smolts at the Fish Farm.
13*