Íslenskar landbúnaðarrannsóknir - 01.09.1978, Page 167

SALMON MANAGEMENT AND OCEAN RANCHING 165
TABLE 3.
Calculated optimum catch
levels at Ellidaár river.
Period At MSY level Exploitation rate M
S R C
1935-67 1,458 3,725 2,266 0.61
1935-55 1,284 3,821 •2,537 0.66
1956-67 1,601 2,983 1,382 0.46
ascent the catch per unit seemingly is
proportional to the magnitude of the in-
coming runs. After the inflection point has
been passed the daily catches are more
stable and probably also are proportional
to the total resident stock in the river,
except that the catchability coefficient has
changed.
One sure and direct way of calibrating
the unit of effort as a time function is to
obtain independent counts of the run as
the fish enter a stream, and to relate the
catch per unit of effort to the total popula-
tion size, introducing other variables such
as water level, temperature, barometric
pressure, and other environmental
parameters which might be of impor-
tance. The predictive power of these fac-
tors can then be studied by a stepwise
regressing program.
At best this is a long, tedious, and time-
consuming study but is of paramount im-
portance for management of the rivers,
especially when we consider the economic
aspects.
The diagrammatic description of the
economics of the lcelandic salmon
fisheries in Fig. 6 has been formulated by
McCaughran (1974). Twodecisions must
be made: setting the number of fishing
rods, which is a government decision, and
fixing a license fee, which is a decision by
the fisheries associations. The fishermen’s
satisfaction is generally accepted to be in-
creasing continuously with the yield per
angling day, while increasing the license
fee and crowding may detract. No attempt
has been made as yet to measure in an
exact manner these functional relation-
ships.
However, a few very important facts
emerge from the Ellidaár data. The op-
timum escapement as defined by a
spawner(S)-recruit (R) relationship
(MuNDYet al. 1978) indicates a total fish-
ing rate as the maximum sustainable yield
(Table 3).
These rates are generally substantially
highter than those generated by the sports
fishery. A first and superficial conclusion
is, therefore, that the fishing effort could
be increased or that the fish could be har-
vested in other ways in this stream.
However, these estimates are point es-
timates based on average conditions.
While a spawner-recruit curve gives the
best mathematical fit, its utility for man-
agement is directly related to the as-
sociated variance. In this case the returns
from an escapement of the size given in
Table 3 may vary from 2,000 to 5,000 fish.
At present there is no way to determine
the size of the incoming run so that deci-
sions must be based on average perfor-
mance. Ultimately, therefore, all
strategies must be based on the risk in-
volved in the different management
schemes. A general form of the expected
utility of a management policy would be
n
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i = i
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