(4.5)
During the meeting of the assessment Working Group (ICES, 1998b) of the Iberic stock (Div. VIIIc and IXa) of hake, Merluccius merluccius, the following stock parameters were estimated for the period 1982-1996:
|
Year |
N (age 0) |
Spawning Biomass |
|
1982 |
125 |
59.8 |
|
1983 |
107 |
61.4 |
|
1984 |
136 |
58.8 |
|
1985 |
97 |
44.1 |
|
1986 |
104 |
26.4 |
|
1987 |
97 |
24.2 |
|
1988 |
84 |
22.8 |
|
1989 |
56 |
18.9 |
|
1990 |
59 |
19.4 |
|
1991 |
69 |
20.5 |
|
1992 |
86 |
21.5 |
|
1993 |
70 |
21.0 |
|
1994 |
63 |
16.5 |
|
1995 |
32 |
15.2 |
|
1996 |
83 |
18.0 |
The annual recruitment at the exploitable phase is considered as being the number of individuals with age 0.
1. Draw the dispersion graph of the resulting recruitments, against the parental spawning biomass.
2. The parameters of Shepherd, Ricker, Beverton & Holt and Deriso S-R relations were estimated and are shown in the following table, as well as the respective determination coefficients, r2:
|
Parameters |
Shepherd |
Ricker |
Beverton & Holt |
Deriso |
|
α (R/g) |
3.50 |
4.43 |
4.91 |
4.40 |
|
k (1000 tons) |
64.94 |
78.13 |
45.39 |
106.27 |
|
C |
3.52 |
|
|
0.896 |
|
r2 |
0.71 |
0.68 |
0.66 |
0.75 |
a) Calculate the expected recruitments in each year of the period 1982-1996 using the four S-R models.
b) The determination coefficient, r2, can be used as an indicator of a good or bad adjustment of the model to the observed data, depending on the number of observations (r2 can be interpreted as a percentage of variation of the observed points that is explained by the model. Values close to 1 indicate a good adjustment and values close to zero indicate a bad adjustment). Using this indicator, make your comments about the adjustments of each model.
