FISHERY BULLETIN: VOL. 70, NO. 3 



20 

 10 

 

 10 





 10 





 10 



1 1 1 1 1 1 1 1 i 1 1 1 1 1 1 1 1 1 rriTni im i n m 



4-6 16-18 28-30 40-42 52-54 64-66 76-78 88-90 100-102 



Catch p«r Single-School S«t (MT) 



Figure 2. — Percentage size-frequency distributions of 

 2,643 single-school summer purse-seine catches of At- 

 lantic menhaden, 1955-62. 



em part of the range during the summer, and 

 progressively smaller schools occurred at lower 

 latitudes. Comparison of the mean catch per 

 single-school set within the four major areas of 

 the summer fishery (Table 1) shows that schools 

 in the North Atlantic Area averaged about 21 

 tons per set and 5 to 9 tons heavier than those 

 in other areas. Schools in the Middle Atlantic 

 Area were intermediate in size, averaging about 

 16 tons per set, while those in the Chesapeake 



Bay and South Atlantic Areas were smallest, 

 averaging about 13 tons per set. 



Size of summer schools declined from* 1955 to 

 1962. The mean catch per single-school set in 

 1955 was 22 tons; it decreased and fluctuated 

 ai'ound 16 tons from 1957 to 1960, and in 1962 it 

 was only about half that in 1955 (Table 1) . This 

 decline was largely attributable to a reduction 

 of school size in the North Atlantic and Middle 

 Atlantic Areas, where decreases in the means 

 amounted to about 40% over the 8-year period. 

 In general, mean school size in the Chesapeake 

 Bay and South Atlantic Areas fluctuated only 

 slightly about their grand means. The high 

 mean for Chesapeake Bay in 1955 resulted from 

 several large single-school catches recorded at 

 the beginning of the fishing season and probably 

 is atypical (see also p. 704). Too few single- 

 school catches were recorded in the South At- 

 lantic Area in 1961 and 1962 (1 and 3, respec- 

 tively) to be considered in calculation of these 

 seasonal means. But in view of the relatively 

 small size of single-school summer catches in pre- 

 vious years, additional data from this area in 

 1961 and 1962 would likely not have influenced 

 the grand seasonal means. 



There was a definite change in the grouping 

 of the fish in autumn. In every year schools be- 

 came noticeably reduced in number in surface 

 waters of the Gulf of Maine in late August or 

 early September, and during late September or 

 early October large masses of fish, or "school 

 aggregations,'" appeared off" Long Island, only 

 to disappear from these waters by mid or late 



' To avoid confusion, the word aggregation is used in 

 this paper in its general meaning and not as defined by 

 Breder (1959). 



Table 1. — Mean size of single-school summer catches of Atlantic menhaden from 2,643 purse-seine sets in the four 

 major statistical areas, 1955-62. The number of sets used in calculating the means are given in parentheses. 



702 



