(6.7.1)
The following table presents the annual total catch Y, (t) and mean biomass , (t) for the fishery of the Iberic stock (Div. VIIIc and IXa) of sardine, Sardina pilchardus, between 1977 and 1996, used by the Working Group of ICES (ICES, 1998a).
Year 
Y (t) 

1977 
125750 
750289 
1978 
139990 
759192 
1979 
153441 
763313 
1980 
191682 
804765 
1981 
214133 
842091 
1982 
204504 
802573 
1983 
181139 
713376 
1984 
202686 
794856 
1985 
204107 
810539 
1986 
180606 
679808 
1987 
168825 
547179 
1988 
158540 
481295 
1989 
137126 
431719 
1990 
139157 
368099 
1991 
127756 
316365 
1992 
126054 
453161 
1993 
138795 
539096 
1994 
132800 
416842 
1995 
121384 
368158 
1996 
111431 
246037 
GROUP I
1. Calculate F_{i} corresponding to each year i.
2. Calculate the biomasses, B_{i}, at the beginning of each year. (Use the procedure proposed by Schaefer, that is, the biomass at the beginning of a year is approximated by the arithmetic mean of the mean biomasses of the previous and the following year).
3. Calculate the equilibrium catches, Y_{E}, which would correspond to the observed values of F.
4. Calculate the equilibrium mean biomasses, E, which would correspond to the observed values of F.
5. Draw the graph of E against F_{i}.
GROUP II
The Schaefer model was adjusted and the following parameters were estimated:
k = 1562851 t
r = 0.426 year^{1}
1. Calculate the equilibrium biomasses and the equilibrium catches corresponding to the fishing levels observed in each year, using the Schaefer model.
2. Draw, in the graph of Group I point 5, the equilibrium biomasses calculated with the Schaefer model.
3. Calculate F_{MSY,} B_{MSY} and Y_{MSY}
4. Calculate F_{0.1,} B_{0.1} and Y_{0.1}.