Íslenskar landbúnaðarrannsóknir - 01.09.1978, Side 171

SALMON MANAGEMENT AND OCEAN RANCHING 169
precludes an in-season adjustment of
fishing mortality as a management option
which is available in commercial salmon
fisheries. Added to this is the high varia-
bility in environmental factors and thus in
total freshwater survival. Finally, there
remains the intangible bqt real problem of
fishermens’ satisfaction and willingness to
pay the set license fee. The logical out-
come of such considerations leads to a
management strategy which provides a
higher stock of spawners than would be
dictated by a straight commercial salmon
fishery, as those existing along the
perimeter of the North Pacific Ocean.
The postwar development in Iceland
has been a continuous and sharp upward
trend in relation to the condition in other
nations, albeit several factors enter in,
such as better record keeping, building of
fishways (Fig. 7) and release of high qual-
ity smolts, but the major reason is the
existence of suíficient escapement to buf-
fer against the large environmental varia-
bility in survival.
Eventually a point will be reached
where the average catches start to level oíf
as the carrying capacity of a river system is
being fully utilized. A next quantum in-
crease of production can then be reached
through smolt releases, both in salmon-
producing streams and in others without a
native stock of salmon. These options
have been discussed elsewhere by Isaksson
et al. (1978).
Other avenues, still somewhat untried,
lie in the construction of spawning chan-
nels or, alternatively, in use of gravel in-
cubators where flooding and scouring are
a source of egg loss. Recent Canadian ex-
periments (Stockner, in press) point to a
successful increase of the carrying
capacity by fertilization of especially con-
structed nursery channels where water
flow is controlled. All remedies of this na-
ture will benefit the recreational fishery.
OCEAN RANCHING
The yield of the Icelandic salmon fishery
is presently increasing. Several factors are
contributing to this trend which has pre-
vailed during the entire postwar period.
In addition, improved hatchery
techniques in later years have permitted
releases of smolts with high survival rates;
this represents a real augmentation of the
natural production of many streams.
As brought out by IsAKssoNet al. (1978),
it appears that hatchery-released smolts
predominantly occupy the lower reaches,
which reduces competition with the indi-
genous juveniles. The Artúnsá experi-
ment (loc. cit.) opens new avenues for in-
creasing the recreational fishery by re-
leasing smolts in streams which normally
are nonproducing entities. Expansion
along these lines necessilates an ever-in-
creasing hatching production of smolts.
At the present time the existing hatch-
ery capabilities in Iceland set an upper
limit for expansion ofsmolt production. A
recommendation of this study is to build
large central hatcheries with a capacity of
1 million smolts or more in order to
minimize the production cost. On the
other side, it is not possible immediately to
acquire the necessary number ofeggs from
a single river or source. To date a number
of different donor streams and release
streams has been used. From the purist
standpoint it can be argued that such
mixing of the gene pool is wrong or less
desirable than using a single stream both
for egg-taking and release.
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