Catch Composition 



Table 8 contains estimates of the Atlantic mackerel 

 catch in numbers at age during 1962-77. Ages ranged be- 

 tween and 10 + . Average age of the catch during the 

 period was 3.6 yr, with annual mean ages ranging be- 

 tween 2.3 and 4.8 yr. In 1977, 45 r c of the catch in 

 numbers was age 3 fish, with a mean age of 3.8 yr. Pre- 

 dominant age groups in the catches have varied, general- 

 ly reflecting the passage of dominant year classes 

 through the fishery. 



Abundance Indices 



United States research vessel bottom trawl survey 

 catch-per-tow data (Table 9) indicate a continued de- 

 cline in Atlantic mackerel abundance. The spring survey 

 catch-per-tow (kilograms) index decreased 37% from 

 1976 to 1977. Both the spring and autumn indices have 

 demonstrated a continuous biomass decline since 1968- 

 69 (Fig. 3). The spring survey mean catch per tow in 

 numbers has also declined continuously (Table 10) and 

 has shown a marked decrease in the number of age 1 

 Atlantic mackerel in 1976 and 1977. 



The standardized U.S. commercial catch-per-day in- 

 dex (Table 11) has generally been consistent with esti- 

 mates of abundance from survey data and with stock 



Table 9. — Stratified mean catch (kilograms) per tow 

 (In and retransformed) of Atlantic mackerel from 

 United States bottom trawl surveys in the spring 

 (strata 1-25, Gl-76) and autumn (strata 1-2, 5-6, 9-10, 

 13, 16, 19-21, 23, 25-26). 



Table 11. — Atlantic mackerel catch per standardized 

 U.S. day fished. 



Spring' 



Autumn- 



Year 



In 



Retransformed 



In 



Retransformed 



1963 



— 



— 



.013 





.016 



1964 



— 



— 



<.001 





COOl 



1965 



— 



— 



.046 





.073 



1966 



— 



— 



.057 





.085 



1967 



— 



— 



.195 





.372 



1968 



.575 



3.998 



.117 





.217 



1969 



.029 



0.065 



.154 





.459 



1970 



.471 



2.039 



.068 





.099 



1971 



.425 



1.969 



.052 





.073 



1972 



.354 



1.332 



.070 





.107 



1973 



.228 



0.748 



.034 





.043 



1974 



.277 



0.769 



.046 





.108 



1975 



.121 



0.255 



.010 





.016 



1976 



.144 



0.317 



.028 





.039 



1977 



.118 



0.199 



— 





— 



'Based on 



catches with No. 



41 trawl; 



1968 



■72 catches 



were 



ivith No. 36 trawl and were adjusted to 



equivalent 



No. 41 catches using a 3.25:1 ratio (41/36). 





-Based on 



catches with No. 



36 trawl. 









Catch per 



day 





Catch per day 



Year 



(metric tons) 



"i ear 



(metric tons) 



1964 



0.43 





1971 



1.29 



1965 



0.49 





1972 



0.84 



1966 



0.84 





1973 



0.53 



1967 



1.75 





1974 



0.17 



1968 



2.80 





1975 



0.53 



1969 



1.92 





1976 



0.59 



1970 



2.07 









biomass estimates obtained from cohort analysis (Table 

 12), although it increased in 1975 and 1976 while the 

 other indices continued to decrease. The U.S. commer- 

 cial index may be limited as a measure of overall stock 

 abundance because it has been based on small inshore 

 catches, and particularly since these catches have com- 

 prised an increasingly smaller proportion of the total 

 catch in recent years. The U.S. Atlantic mackerel catch 

 from directed effort averaged 3.6 ( c of the international 

 catch each year during 1964-67, 1.4% in 1968-69, 0.2% 

 during 1970-76, and <0.1 c c in 1974-75. The increase in 

 the index in 1975-76 may reflect only localized improve- 

 ments in abundance. 



Distant-water fleet catch-per-effort data are con- 

 sidered to be unreliable as a measure of Atlantic mack- 

 erel abundance. Previous analysis of distant- water fleet 

 statistics by Anderson (1976) indicated that various 

 country-vessel tonnage classes experienced different pat- 

 terns of catch per hour fished during 1968-74, most of 

 which were not in agreement with the change in stock 

 biomass determined by cohort analysis. Total stock bio- 

 mass peaked in 1969 (Table 12) and then declined sharp- 

 ly, whereas distant-water fleet catch per effort generally 

 increased or was erratic in year-to-year changes. 

 Anderson (1976) suggested that learning, improvements 

 in vessel efficiency through technological changes, or 

 both occurred in varying degrees for nearly all country- 

 tonnage classes engaged in the Atlantic mackerel fishery 

 which invalidates their catch rates as consistent 

 measures of stock abundance. In view of the previous 

 inconsistency in these data, it is difficult to interpret the 

 current catch rates. Although 1977 data are not avail- 

 able, 1976 data indicated increases in catch per effort for 

 certain Bulgarian, German Democratic Republic, and 

 Polish vessel classes and decreases for some U.S.S.R. 

 vessels. The difficulty in interpreting distant-water fleet 

 catch rates was recognized at the time of the last ICNAF 

 assessment (ICNAF 1977), and it was also felt that a 

 schooling species such as Atlantic mackerel was subject 

 to continued accessibility to fishing gear even at low 

 levels of abundance. 



Table 10. — Stratified mean catch (number) per tow of Atlantic mackerel by year class from the VM'.V 

 bottom trawl surveys in ICNAF Subarea 5 and Statistical Area 6. strata 1-25. (>l-7<» 



7ti U.S. spring 



Year class 



Year 1976 1975 1974 1973 1972 1971 1970 1969 1968 1967 1966 1965 1964 



1963+ -Total 



1973 



— 



— 



— 



— 



1.949 



6.683 



8.188 



15.957 



3.669 



21.081 



6.309 



3.319 



0.365 



0.574 68.094 



1974 



— 



— 



— 



2.067 



0.749 



1.347 



0.185 



0.492 



0.249 



1.401 



0.440 



0.237 



0.107 



— 7.274 



1975 



— 



— 



5.330 



1.101 



0.141 



0.128 



0.030 



0.028 



0.020 



0.014 



0.001 



— 



— 



— 6.793 



1976 



— 



0.447 



4.92S 



0.365 



0.070 



0.014 



0.006 



0.009 



— 



0.004 



— 



— 



— 



— 5.843 



1977 



0.043 



0.254 



0.340 



0.153 



0.050 



0.017 



0.010 



0.024 



0.011 



0.018 



0.007 



0.019 



— 



0.946 



