Íslenskar landbúnaðarrannsóknir - 01.09.1978, Page 99

AN EVALUATION OF TWO TAGGING METHODS 97
fect the length of migration for Pacific
salmon. One possible explanation for the
early arrival of the June smolts in Iceland
is the possibility that they have a shorter
migration, although this remains much an
open question.
SUMMARY OF RESULTS
Comparison of microtags and Carlin tags.
1. Approximately 1.6 microtagged sal-
mon returned for each Carlin-tagged
salmon when released in the same
numbers.
2. There is a strong indication that the
Carlin tags reduced survival in smaller
size classes; the same appeared to be
true for microtags in certain compara-
ble groups. However, other groups of
microtagged smolts did not show any
decrease in survival with decreased
size. The reason for this apparent con-
tradiction could best be explained by
the effects from fin erosion present
primarily in certain smaller fish.
3. The survival ofsmall and medium out-
door smolts was not affected by ventral
fin clips. Large outdoor smolts were
affected by ventral fin clips, indicating
that fin erosion masked the ventral fin
effect in smaller smolts.
4. Upon adult return, the microtagged
salmon were 100-300 g heavier than
the Carlin-tagged salmon, with the
greatest differences in the small smolt-
again suggesting the greater effect of
Carlin tags on smaller fish.
5. The adult weight of small and medium
outdoor smolts was not affected by
ventral fin clips. Large outdoor smolts
were affected by the fin clips, further
suggesting a masking of the clipping
effect by poor fin condition.
6. There were no differences in sex ratios
of returning adults tagged with Carlin
tags and microtags.
7. Tag loss of Carlin tags was approxi-
mately 10% (90% confidence interval
2.4%—17.1 %); plastic tags attached
with polyethylene thread had a mean
loss of 24% (confidence interval,
16.1-33.9%); microtags had a mean
loss of 1.7% (confidence interval,
1.3-2.1%).
Comparison of time and location of smolt re-
leases.
1. Smolt releases above the lagoon at
Kollafjördur Fish Farm were superior
to releases below the lagoon in all com-
parisons.
2. June smolt releases were superior to
May releases, and April releases were
much inferior to all other release times
in all smolt types tested in the 1975
experiments.
3. Smolts released in June were signific-
antly smaller at return than smolts re-
leased in May.
4. Smolts released in June tended to re-
turn earlier as adults than smolts re-
leased in May, which related to size
differences.
ACKNOWLEDGEMENTS
The authors whish to acknowledge the
primary funding of this project by the
United Nations Development Fund, and
the further contriburion by the Indepen-
dence Foundation of Philadelphia,
U.S.A., which funded the data analysis
and project completion. Tony J. Rasch
collaborated extensively with the authors
in the data analysis.
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