# 8.15 Fmed AND FMSY

(5.2.3) and (5.2.4)

During the meeting of the Assessment Working Group (ICES, 1998b) on the Iberic stock (Div. VIIIc and IXa) of hake, Merluccius merluccius, the following population parameters were estimated:

 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

For the long-term projections, the Working Group adopted the mean exploitation pattern for the period 1994-1996, as shown in the next table:

 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

1. Calculate the long-term annual mean biomass, the spawning biomass, the annual catch in weight and the mean weight in the catch.

2. Draw the curve of the annual catch in weight and the mean biomass against F, for values of Ffactor between 0 and 2.5 year-1, with intervals of 0.1 year-1. Calculate the TRPs Fmax and F0.1.

3. Calculate the biological reference point Fmed, knowing the recruitments (million individuals at age 0) and the spawning biomasses (thousand tons) between 1982 and 1996, estimated by the Working Group, presented in the following table:

 Year N (age 0) (million) Spawning biomass (1000 tons) 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

4. Calculate the long-term mean biomass, the spawning biomass, the catch in weight and the mean weight in the catch for Fmed. Compare with the values obtained in question 1 and make your comments.

5. Adopting the Ricker stock-recruitment relation, estimated by the Working Group (a = 4.43 R/kg and K = 78.13 thousand tons), calculate FMSY, BMSY and Y MSY. and compare the different F-target estimated.