Associate Expert FAO
Institut Scientifique des Pêches Maritimes
UNDP/FAO Project MOR/81/002
A multispecies yield per recruit model, based in Beverton and Holt,
is presented in Figure 1.
It is valid for : Boops boops
and Octopus vulgaris
The model includes the biological parameters for each species :
As well as economical parameters for each species :
Dollars/ton at Las Palmas, 1984
The biological parameters were determined based on cruises in the region 22–26°N (Western Sahara, 34.1.3) during 1980–1981–1982–1983 (Mennes, 1984 and Idelhaj, personal communication)
The economical parameters were determined in Las Palmas (Gréboval, 1982).
The yield per recruit is thus expressed in value.
Two cross sections are presented in Figure 2. The first cross section (A) shows that a reduction of fishing by 40% corresponds to MSY, if a mesh size of 60 mm is assumed.
The second cross section (fishing effort = 100%) (B) shows that 2 optima exist : the first one at 124 mm mesh size, the second one at 204 mm mesh size.
Mennes (1984), CECAF/TECH/84/62
Gréboval (1982), CECAF/TECH/82/45
Figure 1 : Plot. Beverton and Holt yield isopleths, valid
for 11 Sparids and 3 Cephalopods. Values for each s[ecoes are included in the model.
Actual fishery effor : 100
Actual mesh size (mm) : 60.
Casablanca, night of 11.12.84 - 12.12.84
Figure 2 : Plot. Beverton and Holt yield isopleths, valid
for 11 Sparids and 3 Cephalopods, values included.
Cross sections on 60mm mesh size and on 100 relative fishery effort.