Íslenskar landbúnaðarrannsóknir - 01.09.1978, Page 107

AN EVALUATION OF SMOLT RELEASES 105
Table 2. The total straying from Ártúnsá
is little less than 30% for the smolts from
the release pond. Strays from the direct
plant are somewhat higher. The majority
of the straying fish went to Kollafjördur or
were caugt at Ellidaár. It is obvious that
the smolts displayed a great tendency to
return to Kollafjördur, their place of birth
and upbringing. One question is whether
the straying pattern worrid have persisted
in a barren stream, physically further
away and with an entirely different water
source. The water source for Ártúnsá and
Kollafjördur is Mt. Esja which may mean
that the water chemistry is very similar.
Higher mineral content and the smell of
salmon in Ellidaár may also be of major
importance. That theory is supported
somewhat by the fact that strays of hat-
cery smolts from Ellidaár to Kollafjördur
were only 2.2%, which is lower than-the
strays from Kollafjördur to Ellidaár. Al-
though a 2 test showed that the differ-
ence in straying between smolts from a
direct plant and a release pond was not
significant at the 0.05 level, there was an
indication that the release pond improved
homing.
Discussion
The release pond technique was first
utilized in the spring of 1974 on the An-
dakílsá, a short stream which flows di-
rectly into the sea at Borgarfjördur in
West Iceland. Possibilities of expansion of
the natural production are none, due to
shortness of the river. The approximate
return rate from the 2-year outdoor smolts
used in that experiment was 4%, with 2%
being caught in the river in addition to the
approximately 200 naturally-produced
salmon being caught in the river each
year.
The Ártúnsá experiment is the first
controlled experiment with direct plant
being done along with a release pond
plant. It demonstrates strikingly that
plants into barren streams should never
be performed without the use of a release
pond. This is even more important when
the smolts have to be transported very
long distances, resulting in weakened
smolts and higher mortality ifreleased di-
rectly into the river.
Judging frorn the experience obtained,
however, it is likely that within the next
fewyears the releases ofsmolts into barren
streams after temporarily holding them in
release ponds, will become a permanent
method in the fish cultural activity in Ice-
land.
RELEASE OF SMOLTS INTO A
PRODUCTIVE STREAM
Description of the stream
The Ellidaár river flows into Faxa Bay in
southwestern Iceland. The river is 6 km
long from the estuary to its outlet at
Ellidavatn lake. In spite of its origin in a
lake, it is highly affected by runoff and
may be subject to considerable flooding,
especially in late winter. The water temp-
eratures are well over 10°C for 3 months
during the summer which is characteristic
of a good salmon-producing strearn.
A trap is located about V3 km from the
mouth of the river (Fig. 3-top). For many
years, the adult salmon were transported
frorn the trap above a hydroelectric dam
on the river. This practice was discon-
tinued more than 10 years ago. A
14