The 1958 purse seine fishery will now be 

 reviewed in the light of the data summarized 

 in the preceding sections of the report and 

 the hypotheses developed there. 



The catch (in tons) in 1958 declined for the 

 third consecutive season and was only 73 per- 

 cent of the record catch in 1956, but 84 per- 

 cent of the average catch for 1952-57. The 

 reasons for the continued decrease are not 

 completely understood, but one of the important 

 factors undoubtedly was the variation in re- 

 lative strength of individual year classes 

 (June, 1961). In 1955, for example a good 

 catch resulted primarily from the combined 

 contributions of two strong year classes, those 

 of 1951 (age-4 fish) and 1953 (age-2 fish). The 

 incoming 1954 year class (age-5 fish) made a 

 weak showing in that year. In 1956, a record 

 catch was produced mainly as a result of the 

 continuing heavy contributions of the 1953 

 (age-3 fish) and 1951 (age-5 fish) year classes, 

 combined with the strong entry of the 1955 

 year class (age-1 fish). The contribution of the 



1955 year class in that year was more than 

 three times that of the 1954 year class at the 

 same age in 1955; the latter year class at age 2 

 in 1956 continued to make a weak showing. 

 Although the catch declined slightly in 1957, it 

 was maintained at a relatively high level by 

 the continuing strong contribution of the 1955 

 year class (age-2 fish) and a strong entry 

 of the 1956 year class (age-1 fish). The 1953 

 (age-4 fish) and 1951 (age-6 fish) year classes 

 also continued to make important contributions 

 to the catch in that year. In 1958, the contribu- 

 tion by the newly recruited 1957 year class 

 (age-1 fish) was the smallest since that of the 

 1954 year class (age 1 in 1955) and amounted 

 to about two-fifths that of the 1955 year class 

 and about one-half that of the 1956 year class 

 at the same age. Catch per unit of effort of 

 the 1957 year class in numbers offish (31,000) 

 was less than half that contributed by the 1955 

 year class at the age 1 in 1956 (65,000) and 

 less than three-fourths that contributed by the 



1956 year class (42,000) in 1957. 



Assuming that the same proportion of each 

 incoming year class was available to the 

 fishery during the past 4 seasons, it would 

 appear that the 1954 and 1957 year classes 



were weak, while the 1955 and 1956 year 

 classes were strong, and the relative strength 

 of each new year class was reflected in the 

 season's catch. 



Contributions by older year classes also con- 

 tinued to decline and in 1958 were the smallest 

 in the past 4 seasons. In 1955, fish of age 3 and 

 older ages accounted for 20 percent of the 

 catch in numbers of fish; in 1956, 16 percent; in 



1957, 9 percent; and in 1958, 4 percent. While 

 data are available for only 4 seasons, it would 

 appear that the increased exploitation of ages 1 

 and 2 (estimated at approximately 20 percent) 

 may have been sufficiently great to have re- 

 moved a disproportionate number of each new 

 year class, with the result that the catch by 

 number (and weight) of older fish has declined 

 accordingly. The apparent decrease in abund- 

 ance of older age groups and the greater 

 dependence on a single year class makes the 

 fishery much more susceptible to wide fluctua- 

 tions in yield in the future. 



In the South Atlantic Area, the 1958 catch 

 was about average for the past 5 summer 

 seasons, but greater than that in the 1957. 

 Based on the unadjusted effort data, it would 

 appear that schools were more numerous than 

 in the previous 3 seasons, but smaller in size. 

 Although earlier year classes at ages 1-3 

 individually made greater contributions to the 

 catch in previous seasons (the contribution by 

 the 1955 year class at age 1 in 1956, for 

 example, was over three and one-half times 

 that of the 1957 year class at the same age in 



1958, and the contribution by the 1955 year 

 class at age 2 in 1957 was over one and one- 

 half times that of the 1956 year class at the 

 same age in 1958), the increased catch in 1958 

 may be traced to the combined contributions of 

 three successive year classes, 1955-57. The 

 mean length and weight of fish in the catch 

 was below that in 1957 and resulted from a 

 greater proportion of age-1 fish (1957 year 

 class). Based on the length-age data presented 

 earlier in this section and discrepancies be- 

 tween this and other areas in year-class 

 strength, recruitment pattern, mean length and 

 weight at each age, and derived total annual 

 mortality rates, it would appear that the 

 summer fishery in the area was dependent 

 upon a separate stock. 



22 



