Íslenskar landbúnaðarrannsóknir - 01.09.1978, Blaðsíða 159

SALMON MANAGEMENT AND OCEAN RANCHING 157
Icelandic salmon stocks against inter-
mingling with foreign stocks.
Absence of a high seas fishery for im-
mature salmon and the abolishment of
coastal and estuarine fisheries in 1932,
which incidentally never developed to any
magnitude, permit assignment of the
catch to each individual river, the first
prerequisite for a rational management of
the fishery.
From the time of the first colonization of
the country the fishing rights were vested
with the property owners, the farmers,
who used the salmon resources for food or
for sale. With the advent of the first British
sports anglers about a century ago a re-
creational fishery for salmon has de-
veloped, which today is economically
more rewarding than a direct commercial
fishery for meat alone.
The studies reported on in this collec-
tion of papers should be seen against this
background. Some of them involve intro-
duction of new techniques with the results
of the initial application. Others deal with
results of long-term studies. But all were
centered around two cardinal questions,
viz., how to manage an existing salmon
fishery for a desired maximum return and
how to increase the yields beyond con-
straints imposed by existing environ-
mental factors.
SALMON MANAGEMENT
A management scheme of a salmonoid
stock essentially must consider the es-
capement. Any attempt to regulate such a
resource for the so-called maximum sus-
tainable yield (MSY) obtained from a
series of different spawner recruit curves
will have as its ultimate consequence a
destruction of the runs. This has been ex-
perienced in a long series of declining sal-
mon fisheries; it can be established for
theoretical reasons and it can be verified
by simulation models. Heuristically the
same result is obtained easily by consid-
ering the large variability in spawner-re-
turn ratios, where a fixed catch quota at
times must coincide with small returns
and depress future runs because of insuffi-
cient escapement.
Regardless of the approach to salmon
management, the need is always present
for an assessment of the escapement. One
attempt through direct electronic count-
ing has been discussed above. However, at
the present time this method is of limited
applicability. Therefore, some eífort was
expended to obtain such estimates from
available catch data.
In its -simplest form the total catch or
the cumulative catch curve at any time
during the fishing season affords a direct
measure of run strength, provided the
catchability coefficient and vulnerability
remain fairly constant from year to year.
Both measures are to some degree depen-
dent upon the nature of a salmon run and
can eventually be expressed as a
mathematical time function.
Normally the salmon ascend in distinct
groups or schools, separated by time in-
tervals of varying length. An accumula-
tion usually takes place in the estuaries
and ascent might be triggered by rain and
a sudden increase in river discharge. In
the Pacific salmon, where this has been
studied in more detail, the entry pattern
can be described as a series of pulses of
different heights, decaying in a negative
exponential manner. Where there are de-
lays, such as at the first waterfall in a river,