Íslenskar landbúnaðarrannsóknir - 01.09.1978, Page 85

AN EVALUATION OF TWO TAGGING METHODS 83
well as on time of downstream or up-
stream migration. Time ofupstream mig-
ration will not be discussed in this report,
but it was checked for the different size
classes and smolt types and was found to
be not signifícant.
Similarly, the effects of fin clips on the
growth ofsalmon and trout are of consid-
erable interest. Fin clips have been a
common way of identifying fish and in
some cases have been used for growth
studies in lakes and rivers. Since we fin-
clipped some microtagged fish for tag-loss
purposes, it is useful and convenient in
order to observe possible growth diíferen-
lials, to compare the weights of adults re-
sulting from microtagged smolts with
microtagged smolts having additional
ventral clips.
An additional question that often arises
in hatcheries is whether the faster-grow-
ing fish in the hatchery are going to grow
faster when out of the hatchery. In order
to test this, one has to be sure that the
populations under study are fast- and
slow-growing and the growth is not being
affected by other factors such as fin ero-
sion and tags. Thus. Thus, we examined
our results in terms of the effects of smolt
type on adult size where tag effects appear
to be understood.
Survival.
Comparison of Carlin tag and microlag.
Survival of Carlin- and microtagged 2-
year smolts in the 1974 and 1975 experi-
ments is shown in Fig. 5. Most striking
observation is that the results from the
1975 experiment are much inferior to
thosefrom the 1974experiment. Thereare
three apparent reasons for this. The first is
based on observation of the 2-year-out-
door smolts in 1975 which were appar-
ently of inferior quality (primarily due to
fin erosion) compared to the previous
year, especially in the small-size classes.
Secondly, the excessive handling of these
fish during the sorting operation may have
been detrimental. The third explanation
lies in the fact that 2-year-outdoor smolts
released in May as these were, did not do
as well as those released in June - a fact
which will be discussed later in this report.
If we consider the 1974 experiment to
represent more normal conditions, there is
a 50-100% difference in survival between
microtags and Carlin tags, which is sig-
nificant at the .05 level. This gives a return
of approximately 1.6 microtagged salmon
for each Carlin-tagged salmon. This is
fairly close to a 1.5-2.0 ratio between Car-
lin tagged and untagged smolts found at
the Fish Farm in the past (Isaksson, 1976).
The 1975 results at least do not contradict
the 1974 evidence of reduced survival
from Carlin tagging.
There is no indication from Fig. 5 that
the Carlin tag affects survival ofsmall fish
more than large, but this problem cannot
be fully understood until we have looked
at other groups of smolts in different size
classes tagged with microtags. In Fig. 5
there is no statistical difference (.05 level)
between the survival ofsmall and medium
smolts, whereas the difference is signific-
ant between the medium and large smolts.
This is true for both the Carlin-tagged
and microtagged smolts.
Effect of ventral fin-clips.
Fig. 6 shows the survival of microtagged
2-year-outdoor smolts in different size
classes. Some of the smolts had only a
microtag but others had an additional