Íslenskar landbúnaðarrannsóknir - 01.09.1978, Page 90

88 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
1-yr
2-yr
PHOTOPERIOD
MICROTAG
PHOTOPERIOD
MICROTAG
2-yr OUTDOOR
MICROTAG
2-yr OUTDOOR
CARLIN TAG
SMALL
MEDIUM
SIZE AT RELEASE
LARGE
Fig. 8. Relationship of sex ratio at return to smolt type and size at release (1974 tagging experiments).
known from the Kollafjördur Fish Farm
that the males are, on the average,
300-400 g heavier than the females. A
considerable difference in sex ratio be-
tween groups could thus affect the average
weight.
Sex Ratios at Return.
The sex ratios of microtagged- and Carlin-
tagged smolts released in three different
size classes in 1974 are shown in Fig. 8.
Looking at the Carlin-tagged 2-year-out-
door smolts we see that the male ratio is
highest in the small smolts, the ratio is
practically even in the medium sized
smolts, and the ratio becomes increasingly
female in the larger smolts. The same
trend is apparent in the microtagged 2-
year-outdoor smolts, although the
medium-sized smolts have a higher ratio
of females. Consequently, the differences
in sex ratio are clearly not tag-induced by
the Carlin tag.
The only group that does not follow this
pattern is the 2-year-photoperiod smolts
which show higher female ratio in the
smallest size class. The same fish had out-
standing survival in that size class and it
remains open to speculation whether
there is any link between these two factors.
In spite of this aberrance, there seems to
be superficial evidence that small (slower
growing) smolts tend to return with a
higher male ratio, but the opposite is true
for large smolts. One possible explanation
for this is the fact that large male smolts
have been observed returning to the sta-
tion after 2-3 months at sea. Some of the