11.1 M. merluccius
11.2 Merluccius spp.
11.3 Conclusions
The long term effect of changes in mesh size has been investigated by:
(a) constructing theoretical curves of the relationship between yield per recruit and age of first capture. These curves have been used to determine the optimum age of first capture for which the yield per recruit is a maximum; andAs in the case of estimating the effects of changes in fishing mortality, a number of assumptions concerning the values of the parameters were used, as shown in the tables.(b) determining the current age of first capture to see how this compares with the optimum age of first capture.
Table 9 and Figure 7 show the theoretical relationship between yield per recruit and age of first capture at the current level of fishing mortality. The optimum age of first capture is at least seven years. By comparison, the current age of first capture is about one year, which is considerably smaller than the optimum value.
Table 11 and Figure 9 show the theoretical relationship between yield per recruit and age of first capture at the current level of fishing mortality. The optimum age of first capture is between four and six years. By comparison the “effective” age of first capture is between four and five years which is somewhat smaller than the optimum value.
For both species but particularly for M. merluccius, the analysis shows that it should be possible to increase the sustainable yield per recruit by increasing the mesh size (and hence the age of first capture).
