(5.3.5 & 5.3.6)
GROUP I
During the meeting of the Assessment Working Group (ICES, 1998b) on the Iberic stock (Div. VIIIc and IXa) of hake, Merluccius merluccius, the recruitment (million individuals at age 0) and the spawning biomass (thousand tons) was estimated for the period 1982-1996. The values obtained are shown in the following table:
|
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 Shepherd S-R relation was adjusted to the pairs of values in the table (r2 = 0.71), and the relation parameters are the following:
α = 3.5 Kg -1
k = 64.94 thousand tons
c = 3.52
1. Draw the dispersion graph of the resulting recruitments, against the parental spawning biomasses.
2. Calculate the expected recruitments in each year of the period 1982-1996 according to the Shepherd S-R model and in the previous dispersion graph, draw the respective curve.
GROUP II
1. Calculate the annual catch in weight and the spawning biomass per recruit for the stock of hake, using the mortality and biological parameters estimated by the Working Group for the long-term projections (given in Section 8.15), namely:
|
Natural mortality coefficient: |
M = 0.2 year-1 |
|
|
|
|
Fishing mortality in 1996: |
F96 = 0.24 year-1 |
Mean weight in the catch (g):
|
Age (year) |
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8+ |
|
|
4 |
37 |
106 |
205 |
358 |
517 |
706 |
935 |
1508 |
Maturity ogive (percent):
|
Age (year) |
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8+ |
|
% maturei |
0 |
0 |
1 |
6 |
20 |
49 |
76 |
91 |
100 |
Mean relative pattern of exploitation of the period 1994-1996:
|
Age (year) |
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8+ |
|
si |
0.001 |
0.11 |
0.398 |
1.3 |
1.261 |
1.019 |
1.473 |
1.874 |
1.874 |
GROUP III
1. Using the results of Groups I and II, calculate biological reference Limit-Points, Floss and Fcrash.
