Íslenskar landbúnaðarrannsóknir - 01.09.1976, Blaðsíða 11

TAGGING EXPERIMENTS AT KOLLAFJÖRÐUR 9
Table 5
Returns from the 1972 Tagging Experiment
Grcxjp number Age of smolt in yea rs Number of weeks in outdoor ponds Number of tagged smolts released Mean length of tagged smolts R e t u r n s
1973 (after one year) 1974 (after two years) Total re- turns Re- turn % Type of experiment
K O.P. Total K O.P. Total
1 2 45 1998 14.2 77 3 80 3 0 3 83 4.1 Production return-rate
2 2 35 1992 16.8 146 2 148 2 0 2 150 7.5
3 2 35 629 19.5 55 5 60 2 0 2 62 9.8
4 2 35 995 14.6 50 0 50 1 0 1 51 5.1 Type of attachment
5 2 35 998 14.6 44 0 44 6 1 7 51 77
6 2 0* 1497 14.8 44 5 49 1 0 1 50 3.3 Photoperiod
7 1 0* 970 14.9 19 0 19 - - 19 1.9
8 2 35 1000 14.0 70 0 70 5 0 5 75 7.5 Fin clip Vs. tag
Total 1-5 ^MM 6612 j 372 10 382 14 1 15 397 6.0 I
m = Kept under artiflcial light for 30 weeks
mm « Excluding fish in photoperiod experiment and fin-clipped
K = Kollafjöröur
O.P.- Other places
released were on the average larger in the
1972 experiment. Any real differences will
be noted in the length/recapture-rate ana-
lysis.
There does not seem to be any difference
in the return-rate of fish tagged with wire
attachement (5,1) and those tagged with
polyethylene attachement (5,1). One intere-
sting difference, though, was a higher return-
rate after two years in the sea of salmon
tagged with Carlin tags with polyethylene
attachement (13% of the total) as compared
to those with Carlin tags with wire (2% of
total). A reasonable explanation for this is
not available. The polyethylene thread used
was not of the conventional type used for
smolt tagging in other countries and was con-
siderably less pliable.
The remrn-rate of one-year-old smolts in
the photoperiod experiment (group 7) is fair-
ly satisfactory compared to two-year-old out-
door smolts of approximately the same ave-
rage size when tagged (e.g. group 4). The
control group (6) is superior to the one-year-
olds but does not compare with a correspon-
ding group from outdoor ponds (group 4).
It is thus clear that the artifical environment
has not been a satisfactory substimte for na-
mre. Another interesting thing is that stray-
ing is greater in group 6 (10%) than in any
other group. The amount of straying in all
other groups combined was only 2,9%.
Group 3 was different from the other
groups in that the smolts had been carrying
the Carlin tag for a year before their re-
lease. These fish were tagged and released
in 1971 as one-year-smolts and subsequently
electrofished in the outlet creek. They were
re-released in 1972 as two-year-smolts. The
effect of this long tag-adjustment time on
remrn-rate is open to speculations.
In spite of a small average size (14,0 cm)