Íslenskar landbúnaðarrannsóknir - 01.09.1978, Blaðsíða 163

SALMON MANAGEMENT AND OCEAN RANCHING 161
Fig. 2. Mean daily catch in Ellidaár averaged for the years 1927-1974.
count, follow the same trend as discussed
above for the total exploitation rates, but
these are lower by 5-10%. This confirms
what long has been known by the fisher-
men, that the best catches are made in the
lower reaches of a stream during the initial
ascent of the salmon. Once the fish move
higher up in the river, the catchability
coefficient declines.
In Ellidaár the total run and thereby
the spawning stock can be estimated di-
rectly from the catches using an average
exploitation rate of 37% based on all the
years 1935-1973, with associated confi-
dence limits ranging from 19-55% on the
95% level. However, it is doubtful that
this rate can be applied directly elsewhere
especially in the larger streams where
there are both variations in vulnerability
and catchability coefficient. The latter
must be seen as a result of the peculiar
nature of the rod and reel fishery where
capture is dependent upon an active re-
sponse of the fish itself striking after a lure.
Changes in catchability are also a sea-
sonal time function which can be explored
further by the average daily landings in
Ellidaár for the years 1935-1973 (Fig. 2).
The left limb of the curve ascends as
would be expected with a normal dis-
tribution of entries. But the descending
limb declines as a step function and re-
mains constant at several levels.
The uniqe records being maintained for
the Icelandic salmon streams permit a
further exploration. In the river Laxá the
daily landing through one season like 1973
follows the same average pattern as dis-
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