S 3 



SPRING 



AUTUMN 



--J-— T 



Figure 3.— Stratified mean catch (kilograms) per tow of Atlantic 

 mackerel from the U.S. spring (1968-77) and autumn (1963-76) bottom 

 trawl surveys. 



2£ 



X 



o 



1968 



1970 



1972 



1974 



1976 



YEAR 

 Figure 4. — Exponential curve calculated through 1968-77 time-series 

 (1969 point omitted from calculation of curve) of spring survey catch- 

 per-tow (kilograms) indices for Atlantic mackerel. Equation for the 

 curve is: Y = 6.382 exp (-0.345 A'), r = 0.976. 



fitting an exponential curve by least squares to the data 

 points (Fig. 4), and the predicted values calculated from 

 the curve were used in place of the original values to 

 determine the fishing effort index. Cohort analysis (Pope 

 1972) was performed using F = 0.30 for ages 4 and older 



Table 3. — Fishing mortality rates (F) for Atlantic mackerel in ICNAF Subareas 3, 4, and 5 and Statistical Area 6 derived from cohort analysis 



with natural mortality (A/) = 0.30. 



Year 

















Year 



















class 



1962 



1963 



1964 



1965 



1966 



1967 



1968 



1969 



1970 



1971 



1972 



1973 



1974 



1975 



1976 



1977 



19.M 



(.038) 



— 





— 



— 



— 



— 





— 





— 



— 



— 



— 



— 



— 



1952 



.030 



1.0421 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



1953 



.088 



'(.0421 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



1954 



jit:; 



.019 



'(.039) 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



1955 



.043 



.006 



'(.039) 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



i956 



.050 



.006 



.033 



'1.0521 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



1957 



.051 



.017 



.321 



.713 



'(.060) 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



1958 



.127 



.313 



.374 



.946 



.288 



.357 



(.1551 



— 



— 



— 



— 



— 



— 



— 



— 



— 



1959 



.030 



.067 



.066 



.095 



.163 



.446 



.156 



.336 



'(.185) 



— 



— 



— 



— 



— 



— 



— 



1960 



.006 



.004 



.014 



.025 



.054 



.060 



.013 



.039 



.090 



'(.2681 



— 



— 



— 



— 



— 



— 



1961 



.030 



.010 



.012 



.016 



.026 



.040 



.007 



.042 



.195 



.262 



'(.3161 



— 



— 



— 



— 



— 



1962 



— 



.004 



.032 



.018 



.023 



.041 



.119 



.049 



.369 



.291 



.500 



(.451) 



— 



— 



— 



— 



1963 



— 



— 



.044 



.017 



.034 



.032 



.200 



.059 



.145 



.150 



.670 



.892 



'(.515) 



— 



— 



— 



1964 



— 



— 



— 



.024 



.042 



.107 



.351 



.081 



.142 



.290 



.239 



.426 



.575 



'(.532) 



— 



— 



1965 



— 



— 



— 



— 



.028 



.045 



.149 



.249 



.162 



.342 



.47(1 



.449 



.596 



.503 



'(.745) 



— 



1966 



— 



— 



— 



— 



— 



<.001 



.039 



.136 



.207 



.472 



.419 



.283 



.454 



.474 



2.002 



.390 



1967 



— 



— 



— 



— 



— 



— 



.027 



.064 



.181 



.327 



.441 



.465 



.580 



.686 



.888 



.390 



1968 



— 



— 



— 



— 



— 



— 



— 



.003 



.030 



.097 



.215 



.409 



.507 



.536 



.990 



.390 



1969 



— 



— 



— 



— 



— 



— 



— 



— 



.077 



.173 



.246 



.410 



.410 



.523 



.787 



.390 



1970 



— 



— 



— 



— 



— 



— 



— 



— 



— 



.056 



.091 



.545 



.430 



.547 



.598 



.390 



1971 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



.015 



.305 



.598 



.551 



.708 



.390 



1972 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



.168 



.463 



.469 



.916 



.390 



1973 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



.058 



.452 



.652 



.390 



1974 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



-.202 



-.330 



J .220 



1975 



— 



_ 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



— 



'.018 



-.067 



1976 





— 







— 



— 



— 







— 





— 





— 



— 



-.006 



F 



.038 



.042 



.039 



.052 



.060 



.111 



.155 



.144 



.185 



.268 



.316 



.451 



.515 



.532 



.745 



J .390 



(age 3+ I 1 

































'Mean F for age 3+ assumed. 



-Determined from assumed stock size and known catch. 

 Weighted by stock numbers at age from Table 12. 

 'Age 4 + . 



