Íslenskar landbúnaðarrannsóknir - 01.09.1978, Page 55

SPAWNER-RECRUIT RELATIONSHIP 53
method from which the rod and brood
stock removals below the trap were sub-
tracted from the estimated total run size.
Rod catch below the trap, Col. 3, RB,
rod catch above, Col. 4, RA, and total rod
catch, Col. 5, RT, are never estimated.
Stock removals below, Col. 6, BB, were
estimated as:
BBí+i= (BBi/TBi)TB;+i where TB, is
total brood stock in year i.
Brood stock above, Col. 7, BA, is esti-
mated as:
BAi+i = (Bai/TBi)TBi+i
Total brood stock removals, Col. 8, TB,
are estimated as:
A
TBk = TBi where i is the year with the
most similar trap count, within the
stratum, to k. Strata are defmed later.
Brood stock removals are usually prop-
ortional to trap count. Commercial re-
movals, Col. 9, CR, are estimated as:
CRl953 = CRl949
CRl958 = CRl956
A
CR1963-66 = C R1962
A ....
CR1968-74 = 50 based on historical m-
formation.
The figures of Table 4 were compiled
using the following protocol; Total run,
Col. 2, TR, is given by
TR = TC + RB + BB
River spawners, Col. 3, RS, is given by
RS = TR — (CR+BA+RA), the
spawning stock below the trap is consi-
dered negligible for the purposes of this
study since the river below Arbaer dam is
frequently drawn down to very low levels.
Brood stock, Col. 4, BS, is the number of
fish actually stripped according to hatch-
ery records. Since the assumption of a 1:1
sex ratio is imlicit in this work, BS = 2- (no.
females stripped) whenever this figure
was available. Hatchery losses prior to
stripping were not uncommon.
Total, Col. 5, TOTL, is the sum ofCols.
3 and 4. This is the number of spawners
for the spawner-recruit relation. The na-
ture of tagging information available does
not permit separation of the contributions
of the river and hatchery spawners to the
total run.
The recruits, Col. 6, represent the total
production in numbers by the spawners in
the adjacent column. The entries for year
n were computed by multiplying the total
run ofyears n + 4, n + 5, n + 6 by 0.22, 0.72,
0.06, respectively, and summing the re-
sults. The proportion in each age class has
been determined by Fridriksson (1940)
and Poe (1975).
R/S, Col. 7, is the indicated ratio of
Cols. 6 and 5.
Table 3 was generated by nonlinear
least squares regression using the two-
parameter Ricker equation (Ricker 1975,
11.15). The data were stratified a priori
into documentary periods one
(1935-1955) and two (1956-1970) on the
basis of considerations discussed above.
RESULTS
For the case of all data considered to-
gether, the long-term mean case, the data
do support the general contentions of the
Ricker model. The replacement level of
the stock is 3417, and the maximum re-
cruitnrent is 3717. The MSY is 2032 from

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