Catches in the intervening years were estimated by as- 

 suming that the ratio between catch and stock biomass 

 from cohort analysis using only commercial data (ICNAF 

 1977) in each of the above years was the same in the 

 preceding and succeeding 2 yrs, with the exception that 

 the mean of the 1970 and 1974 ratios was used for 1972, 

 and the mean of 1974 and 1976 was used for 1975. 



The 1962-75 numbers at age from the commercial 

 catch were taken from Anderson et al. (see footnote 2). 

 The 1976 numbers at age were revised from those used in 

 the last ICNAF assessment (ICNAF 1977). The general 

 procedure used previously was to: 1) apply the length 

 frequencies and age-length keys reported by individual 

 countries to their catches to obtain numbers at age by 

 country, 2) combine all such numbers at age for respec- 

 tive countries, and 3) prorate the summed numbers at 

 age upwards to include catches from countries lacking 

 sampling data. However, since significant differences 

 were evident among age-length keys submitted by 

 various countries for 1976 (Anderson et al."), it was 

 decided to combine country age-length keys by quarter. 

 The procedure used was to: 1) determine numbers at 

 length by country by month from available length fre- 

 quencies and corresponding catches, 2) combine the 

 numbers at length by quarter and prorate upwards to in- 

 clude country catches lacking sampling data, 3) apply 

 the combined quarterly age-length key to the quarterly 

 numbers at length to obtain quarterly numbers at age, 

 and 4) combine the quarterly numbers at age to obtain 

 the annual numbers at age. The estimated numbers at 

 age for 1977 were determined by applying the above pro- 



United States recreational fishery for Atlantic mackerel. Int. Comm. 

 Northwest Atl. Fish. Res. Doc. 76/XH/142, Ser. No. 4038 (mimeogr.). 7 p. 

 "Anderson, E. D., C. F. Cole, and P. W. Wood. 1976. Variability in 

 mackerel age data reported to ICNAF. Int. Comm. Northwest Atl. Fish. 

 Res. Doc. 76/XW146. Ser. No. 4042 (mimeogr.), 13 p. 



Figure 1. — Northwest Atlantic from North Carolina 

 to Labrador showing ICNAF Subareas 3, 4, and 5 and 

 Statistical Area 6. 



cedure to the available January-March catch and sam- 

 pling data and then prorating the results upwards to 

 include the catch expected to be taken during the re- 

 mainder of the year. Numbers at age for the 1962-77 

 commercial catches were prorated upwards to include 

 the added U.S. recreational catches. 



Mean weights at age (Table 1) adopted by ICNAF 

 (1974) and used in previous assessments were employed 

 in the present analysis. These values were applied to the 

 numbers-at-age catch data for 1962-77 to obtain calcu- 

 lated catches which were compared with the observed 

 catches. These values were also applied to the stock size 

 numbers at age calculated from cohort analysis to obtain 

 stock biomass values. The summed biomass values for 

 each year were adjusted using the appropriate ob- 

 served/calculated catch ratios. The mean weights at age 

 were used unadjusted in the projections of catch and 

 stock biomass for 1978-79. 



Table 1.— Mean weights at age 

 (kilograms) for Atlantic mackerel 

 (ICNAF 1974). 





Mean 





Mean 



Age 



weight 



Age 



weight 



1 



0.095 



6 



0.506 



2 



0.175 



7 



0.564 



3 



0.266 



8 



0.615 



4 



0.350 



9 



0.659 



5 



0.432 



10 + 



0.693 



Stratified mean catch-per-tow (kilograms) indices for 

 Atlantic mackerel were calculated from U.S. research 

 vessel spring (1968-77) and autumn (1963-76) bottom 

 trawl surveys conducted in SA 5-6 in which sampling is 

 based on a stratified random design (Cochran 1953) and 

 strata (Fig. 2) constitute different depth zones and areas 

 (Grosslein 1969). Survey methods, procedures, and gear 



