Íslenskar landbúnaðarrannsóknir - 01.09.1978, Page 56

54 ÍSLENZKARLANDBÚNAÐARRANNSÓKNIR
TABLE 5.
Ricker curve paramelers
All years combined
= 4.3405 = 0.0004296
Replacement level = 3417
Smax = 2328
Rmax = 3717
Smsy = 1365
Rmsy = 3296
Slope al replacement =-0.46799
Residual mean square = 1014071
1935—1955
= 5.7049 = 0.00058893
Relacement level = 2957
Smax = 1698
Rmax = 3564
Smsy =1120
Rmsy = 3304
Slope at replacement =-0.74133
Residual mean square = 1180410
1956—1967
= 3.0778 = 0.0003027
Relacement level = 3714
Smax = 3304
Rmax = 3741
Smsy = 1570
Rmsy = 3004
Slope at replacement =-0.12422
Residual mean square = 499702
a run of 3296 (Table 5). The maximum
rate of replacement is 4.3 recruits/
spawner.
For the first documentary period, the
model suggests that the rebound potential
of the stock was higher than the long-term
mean. The maximum rate of recruitment
for this period is 5.7 recruits/spawner.
The replacement level of the stock is lower
than the long-term mean at a level of2957.
Fig. 1. Spawner recruit curves, Ellidaár river.
------------------ All years combined
------------------ 1935-1955
—————————— 1956-1967
This implies that the capacity of the river
during this time was lower than the long
term mean conditions. The MSY is 2184,
which is higher than the mean since the
maximum rate of recruitment is much
higher for the first documentary than for
the mean.
In the second documentary period (Fig.
1) the replacement point has been shifted
positively relative to the mean. The esti-
mate of MSY is 1434 fish on a recruitment
of 3004 based on twelve data points. The
maximum rate of replacement is 3.1 re-
cruits/spawner and it is a good indication
that the increased number of spawners
during this era is yielding recruits at a
diminishing rate of interest. The residual
mean square of the three data groups indi-
cates the magnitude of the error of the fit
for each.
For the long-term average group esti-
mated recuits, É. has 77% confidence in-