Íslenskar landbúnaðarrannsóknir - 01.09.1976, Page 23

TAGGING EXPERIMENTS AT KOLLAFJÖRÐUR 21
Table 2
Comparlson of Treatment and Returns of One- and Two-Year-Old Smolts
from 1969 - 1973 Tagging Experiments
Year of release Year of return Age of smolts Tag type Number tagged Return % Treatment of smolts
1969 * 1970 1-year Carlin 2413 0 Smolts subjected to intensive indoor rearing
2-year Carlin 2324 10 Smolts put in outdoor ponds 35 weeks before release
1970 1971 1-year Carlin 9200 0.01 Smolts subjected to intensive indoor rearing
1971 1972(73) 1-year Carlin 5250 0.32 Smolts put in outdoor ponds 12 weeks before release
2-year Carlin 583 0.51 Smolts put in outdoor ponds 10 weeks before release
2-year Carlin 3775 4.6 Smolts put in outdoor ponds 35 weeks before release
1972 1973(74) 1-year Carlin 970 1.9 Smolts subjected to artificial photoperiod for 30 weeks
2-year Carlin 1500 3.3 Smolts subjected to artificial photoperiod for 30 weeks
2-year Carlin 6600 6.0 Smolts put in outdoor ponds 35 weeks before release
1973 1974 1-year Plastic 2800 8.5 35 weeks of natural photoperiod throuqh transparent roof
1-year Adipose** 2300 g j 35 weeks of natural photoperiod 1 through transparent roof
2-year Plastic 1000 9.5 Smolts put in outdoor ponds 35 weeks before release
h Gudjonsson 1970
xx Fin-clip
rearing house into outdoor dirt ponds. Once
in these ponds they were fed with capelin
but before they had been fed either Ewos or
an Icelandic dry feed that was being deve-
loped by the Icelandic Fisheries Laboratories.
The fish were kept in the outdoor ponds for
10—12 weeks and released in late May. A
control group of two-year-smolts reared in-
door was treated the same way.
2. The Electric Fishing.
Earlier experiments had indicated that the
one-year-fish had a tendency to linger in
freshwater after their release. The outlet
creek of the station was therefore fished with
an electric shocker to get an indication of the
success of the treatment. It was assumed that
if the treatment of the one-year-smolts had
been successful they would migrate out to sea
to the same extent as the two-year-smolts.
The groups tagged and the recaptures in
the electric fishing are shown in Table 1. It
is evident from the table that both one and
two-year-smolts (groups 1—5) are reluctant
to migrate to sea if they do not get sufficient
time of natural photoperiod. Only groups 6
and 7 were practically absent in the creek
and only they had 35 weeks of outdoor re-
aring, three times more than any of the other
groups.
3. The Adult Return.
The returns of one and two-year-smolts for
five years with corresponding photoperiod
treatments are shown in table 2. The 1969
and 1970 releases of one-year-smolts clearly
show that these fish had a very poor return
rate compared to two-year-smolts from out-
door ponds. The one-year-smolts released in
1971 after a 10 weeks exposure to natural