Data on age composition of catches and fishing efforts for 1979/80 - 1987/88 were used to analyse N. guntheri stock status. On the basis of these data using VPA method with different adjustments stock estimates were obtained. Instantaneous natural mortality coefficient was M = 0.7 - 0.9 (Atlantic Fisheries Research Institute data). To estimate terminal value of instantaneous fishing coefficient (F) different adjustments were used. Long-term mean of F, Gamma method, Pope and Shepherd method, using F regression on fishing effort and using average weighted F. Prior to the beginning of fishery N. guntheri abundance was estimated as 227 thousand tons (using all the above-mentioned methods). For 1986/87 the figure was only 102 thousand tons when calculation was done using regression equation and 160 thousand tons when the Gamma method was used (actual values of first and second age groups abundance were not taken into consideration). Of all these methods adjustments of F using the regression equation at which the correlation coefficients were the highest is the most preferable. Taking into consideration the fact that in the 1986/1987 season the recruitment in the first age group was not less than long-term mean (5947 million specimens), the abundance of N. guntheri in 1987/77 was 152 thousand tons. Then the following TAC values were obtained :
a) Fishing intensity (F) in the predicted period is equal to the mean value of fishing mortality for the main commercially taken age groups (2 - 4 years);
b) Fishing intensity in the predicted period is at the level of 1987/88;
c) Fishing intensity in the predicted period is F0.1.
In the first two cases TAC is 12.3 - 12.7 thousand tons and in the third case - 32.3 thousand tons. The analysis of estimations demonstrates that at the current level of fishing (1987/88) the size of the stock of N. guntheri will remain unchanged.
Document Number:
WG-FSA-88/33
Agenda Item(s)
Abstract