Íslenskar landbúnaðarrannsóknir - 01.09.1976, Page 5

ÍSL. LANDBÚN.
j. agr. res. icel. 1976 8, 1-2: 3-13
The Results of Tagging Experiments
at the Kollafjörður Experimental Fish Farm
from 1970 through 1972
Árni Ísaksson
Institute of Freshwater Fisheries,
Reykjavík, lceland.
ABSTRACT
This paper deals with Salmon Tagging Experiments carried out at the Kollafjörður Experimental
Fish Farm from 1970 through 1972. All the tagging done in these experiments involved
Carlin tags* except for occasional fin clips. Emphasis was placed on the improvement of returns
of one-year-smolts and comparing one-and two-year-smolt return rate. The main findings were as
follows:
1. One-year-smolts tended to remain in fresh water past their migrating period in the first two ex-
periments where they had been exposed to a 0—10 week natural photoperiod. In the last one,
where they were exposed to a 30 week natural photoperiod, they migrated actively out.
2. The return rate of one-year-smolts increased from 0.01% in the 1970 experiment to 1.9% in
the 1972 experiment.
3. One and two-year-smolts subjeaed to a 10 week natural photoperiod before release exhibited
low return rates but better than fish kept in a constant light photoperiod indoors up to the time
of release.
4. Comparable return rates were obtained with Carlin tags attached with either polyethylene thread
or steel wire.
5. Straying of salmon to other rivers during this period was considerably lower than in early years.
6. The total return rate for tagged and untagged smolts in the 1971 experiment was 7.5% but
was closer to 11% in the 1972 experiment.
Introduction.
The Kollafjörður Fish Farm offers excellent
facilities to study absolute return rates
of Atlantic salmon since the smolts are re-
leased from the Fish Farm and return as
adults to a trap where every fish is handled
and inspected for tags or finclips. All the
pertinent background information on the
Fish Farm in presented by GuðjÓNSSON
(1967,1970 and 1972). The results of
tagging experiments from 1965 through
External tag attached through the dorsal musculature under the dorsal fin on salmon smolts.