FISHERY BULLETIN: VOL. 69, NO. 4 



Table 2. — Percentage contribution (in number of fish) 

 of each age-group in the Bay of Biscay from 1967 

 through 1970. 



Age-group 



Year 



1967 



1968 



1969 



1970 



Mean 



00.0 

 01.9 

 78.0 

 16.3 

 03.8 



01.1 

 05.6 

 54.9 

 37.5 

 00.9 



00.0 

 03.9 

 74.6 

 19.5 

 02.0 



00.0 

 32.5 

 34.7 

 24.3 

 08.5 



00.3 



no 



60.5 

 24.4 

 03.8 



100.0 



Table 3. — Calculated numbers of fish and corresponding 

 weights for a cohort of 1,000 albacore and estimated aver- 

 age annual catch in number and by age groups from 

 1963 through 1968 from the Bay of Biscay. See text 

 for explanation of procedures. 



Age 



Cohort 



Weight 



Estimates for an 

 average year's cotch 



Weight 



Total 



1,000 



7,109,078 



45,394.7 



Biscay from 1963 through 1968 was 45,400 met- 

 ric tons (data from Food and Agriculture Or- 

 ganization, 1969). I assumed that the average 

 percentages obtained for 1967 through 1970 were 

 also representative of the years 1963 through 

 1968. 



I used proportion to estimate the average an- 

 nual catch from the Bay of Biscay in number 

 of fish using the total weight of the cohort, the 

 number in the cohort, and the average annual 

 weight of the Bay of Biscay catch. This total 

 was then separated into age-groups (Table 3) 

 using the percentages in Table 2. 



I used these figures to reconstruct three theo- 

 retical albacore populations in the North Atlantic 

 based on total mortality coefficients of 0.50, 0.96 

 (determined from length frequencies), and 1.40 

 (Tables 4, 5, and 6). In each case I began the 

 calculations using the estimated number of 3- 

 year-old albacore landed. I assumed a natural 

 mortality coefficient (M) of 0.23 and obtained 

 the fishing mortality coefficient (F) by subtrac- 

 tion. I used the number of 3-year-olds landed 

 (Ls), fishing mortality (F), and total mortality 



Table 4. — Theoretical albacore population in the North 

 Atlantic, ages 1 through 5, based on a total mortality 

 coefficient (Z) of 0.50 from age 3 through 5. See text 

 for procedures. 



Age 



Number 

 of fish 



Total 

 deaths 



Natural 

 deaths 



Fishing 



deaths 



(surface 



only) 



thousands 

 33,372 



26,514 



20,241 



12,276 



7,445 



thoujandl ol fi'h 



0.23 6,858 6,837 21 



0.27 6,273 5,491 782 



0.50 7,965 3,664 4,301 



0.50 4,831 3,096 1,735 



0.50 2,930 .. 270 



Table 5. — Theoretical albacore population in the North 

 Atlantic, ages 1 through 5, based on a total mortality 

 coefficient (Z) of 0.96 from age 3 through 5. See text 

 for procedures. 



Table 6. — Theoretical albacore population in the North 

 ■Atlantic, ages 1 through 5, based on a total mortality 

 coefficient {Z) of 1.40 from age 3 through 5. See text 

 for procedures. 



854 



