Íslenskar landbúnaðarrannsóknir - 01.09.1978, Page 124

122 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
TABLE 3.
Thc rclalive survivals that must be achieved by difFerent sizes at release in order to produce equal numbers
of adult returns.
Relative survival of l-year smolts from release to return.
12 cm 14 cm 16 cm
heatec stagc val of from utdoor urn. 0.5 0.5 1 1.51 1.78
v = S £ | ® S
-si g 2 -S - o 1.0 1 1.42 1.65
1: bo o U c Q. 'C elative -year laceme onds ui 1.5 1.5 1 1.35 1.51
o? (n a q,

w bo «5 2 V l/> 0 1 8 ■ -n ° 0.5 1 1.35 1.94
Zli O <N 3 >2 © o a •—. r* t-i 3 c rs ® 1.0 1 1.74 1.92
45 .5 -= <A C c
4 ponc water i rearing Relativ< 2-year placem< ponds u 1.5 1.5 1 1.31 1.89
The relationship of survival to size at
release becomes better understood when
the returns f'rom the 1974 and 1975 ex-
periments were analyzed. Table 3 shows
what the relative survival rates would
have to be so that the total returns would
be the same whether 12-cm, 14-cm, or
16-cm fish were raised. Use of this table
will help determine which policy should
be followed in light. of the 1974 experi-
ments. As an example, suppose that four
heated ponds are to be used and the survi-
val of 12-cm fish is 9%. Then, more or
fewer returns could be expected from a
policy of raising 14-cm fish, depending on
whether or not their survival rate was
greater than or less than 9X 1.34 = 12%.
The number of returns cannot be the
sole basis for determining which policy to
follow. Other considerations are the food
costs under various policies and the
weights at return which may be related to
size at release.
CONCLUSIONS AND RECOMMEN-
DATIONS
A method for hand-computing some
hatcher)' management options was de-
veloped. When better data become av-
ailable, the methods can be refined, and
computations done to date should be
scrutinized. Data which are especially
needed are:
1. Growth rates for various fish sizes and
water temperatures.
2. Maximum densities in the several
kinds ofponds for various fish sizes and
water temperatures.
3. Overwinter mortality in the outdoor
ponds.
The results of calculations and obser-
vations have shown that Kollafjördur
Hatchery is presently being run with a
high degree of efficiency and thoughtful-
ness. Innovative ideas are being tested
and experiments are being conducted that
will make the operation even more effi-