Íslenskar landbúnaðarrannsóknir - 01.09.1978, Blaðsíða 18

16 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
Fig. 2. Commercial gillnetting for salmon, in the river ölfusá, Southern Iceland. Photo Thór Gudjónsson.
peated in 1969 and 1970. Thepoor catches
in the river from 1971-1974 had other
causes. On May 5, 1970 an eruption
started in the volcano Hekla in southern
Iceland, and ashes fell on the MidQardará
watershed (Thórarinsson 1970), appar-
ently killing salmon parr and smolts in the
river system. The catches of 803 fish were
way below average during these years, but
in 1975 it reached 1,414 fish, which was
close to the 5-year average ending in 1965.
Ashes also fell on the watershed of the
neighbouring river Vídidalsá to the east,
but did not seem to have as ill effect there
as in the Midfjardará river system.
Salmon migration in the North Atlantic
Salmon smolts released from the State
Experimental Fish Farm at Kollafjördur
have been tagged with Carlin external
taags every year since 1966 and with mic-
rotags since 1974 (Gudjónsson 1970;
Isaksson, and Bergman 1978). The tagging
was primarily carried out to determine the
survival of artificially reared smolts. Some
information has also been gathered about
homing and migration.
During the years 1966-1974, a total of
82,687 1- and 2-year smolts was tagged of
which 2,614 returned to the Fish Farm.
The 1-year smolts tagged from
1966-1970, 14,516 in number, resulted in
only five returns, whereas 8,960 2-year-
olds resulted in 351 returns or 3.9%. The
1- year-olds had been reared indoors un-
der electric light all winter, whereas the
2- year-olds had been outdoors for a year.