Íslenskar landbúnaðarrannsóknir - 01.09.1976, Síða 17

TAGGING EXPERIMENTS AT KOLLAFJÖRBUR 15
salt water lagoon. The total number of tagged
two-year-smolts was 6000. The number of
one-year-smolts tagged was 2800 and an
additional 2300 were adipose clipped. Only
430 smolts were released from the floating
pen.
1. Two-year-smolts.
Using two-year-smolts, comparisons were
made between Carlin tags with conventional
steel wire, Carlin tags with polyethylene at-
tachment, and plastic tags with polyethylene
attachment from Neii and Sons in England.
The progeny of grilse were compared with
the progeny of older salmon to see whether
any inherited differences in age of return
would show up.
One group of two-year-smolts was cold
branded with an X on the left side in ad-
dition to a Carlin tag so that the returning
fish could be checked for the visibility of the
brand. The branding equipment used was
similar to the one described by Mighell
(1969). Branding time was approximately 2
seconds.
2. One-year-smolts.
The one-year-smölts released from Kolla-
fjörður Fish Farm in 1973 had been sub-
jected to a natural photoperiod through a
transparent roof for 35 weeks. The tempera-
tures were kept relatively high except for a
period of 2 months in Jan.—Feb. of 1973
when the natural temperatures were used to
imitate winter conditions. The photoperiod
treatment of one-year-smolts was a continua-
tion of a photoperiod treatment with artifi-
cial light performed in 1971 —1972 which
increased remrns of one-year-smolts consi-
*
derably above previous levels (Isaksson
1976).
The one-year-smolts were all tagged with
plastic tags with polyethylene thread made
by Neil and Sons in England. These fish
were subjected to various treatments before
their release in 1973. One experimental
group was exercised for a period of one
month before release. A control group was
kept in the same type of rearing unit without
exercise. Peterson (1973) has reported in-
creased returns of one-year-smolts in Sweden
by giving them fatty diet for a short period
before release. One group in the present ex-
periment was fed for a period of one month
a modified fatty diet from Fiskfóður h/f, an
Icelandic manufacturer of fish feed. The fatty
diet was formulated by Dr. Jónas Bjarnason
of the Icelandic Fisheries Laboratories. A
control group was fed a regular, nonfatty
diet from the same producer. In addition to
the tagged fish, a large group of one-year-
olds was adipose clipped to get an indication
of the survival of untagged fish.
RESULTS
I. T-wo-year-smolts.
The groups tagged in 1973 and the remrn
of grilse in 1974 are shown in table 1. The
returns of two-year-smolts range from 9,3 to
II, 6 percent. Since the smolts vary in average
length at tagging, apparent differences in
remrns may not be significant. Certain things,
however, are clear. There is no significant
difference in the returns of group 3, being
the progeny of grilse, and group 5, being
progeny of older fish. This supports previous
observations at the Fish Farm. There does
not seem to be any significant difference
between the English plastic tag and the
Swedish Carlin tag, comparing groups 2 and
6. Group 1 having a modified Carlin tag
with polyethylene thread does seem to have a
better return rate than the regular Carlin
tag (group 2).
The fish in group 7 were inspected for
cold brands upon their return. Out of 77 fish
that were inspected, only 38% of the brands