FISHERY BULLETIN: VOL. 69, NO. 4 



Table 9. — Mean number of purse-seine sets per day, Atlantic menhaden fishery, by port and vessel class. 



of sets in Chesapeake Bay, reflecting the increase 

 in effort, was more than double the number in 

 any other area. 



There also were differences in the mean num- 

 ber of sets per day between areas (Table 11). 

 Generally, the greatest number of sets per day 

 was made in Chesapeake Bay, where vessels 

 averaged about 0.10 set per day more than ves- 

 sels in the Middle Atlantic. The fewest sets per 

 day were made in the South Atlantic, where the 

 tendency of schools to disappear by midday 

 limited fishing to the forenoon, and in the North 

 Carolina fall fishery, where the huge schools of 

 fish enabled the vessels to load with relatively 

 few sets. 



CATCH PER SET 



The mean catch per set varied monthly and 

 annually in each area (Table 12). In all areas 

 except the North Atlantic, it tended to be smaller 

 during the middle part of the season than during 

 the early or later part. In the Middle and North 

 Atlantic areas, it averaged 9 tons more in Octo- 

 ber than in any other month. Annually, it fluctu- 

 ated randomly in all areas except the Middle 

 Atlantic, where it decrea.sed after 1962. 



Since purse seines tend to capture an entire 

 school, the mean catch per set is an estimate of 

 mean school biomass. 



The school biomass apijears to increase as the 

 average age of the fish constituting the .school 

 increases. The catch per set in the North At- 



lantic, where 3-year and older fish constitute the 

 bulk of catch, was higher than in the South At- 

 lantic and Chesaijeake Bay, where 1- and 2-year- 

 old fish compose most of the catch (Nicholson 

 and Higham, 1964). In the South Atlantic in 

 1960 and 1961, and in Chesapeake Bay in 19-58, 

 1960, and 1961, when 2- rather than 1-year-old 

 fish composed an unusually high percentage of 

 the catch (Nicholson and Higham, 1964), the 

 mean catch per set was relatively high. In the 

 Middle Atlantic area in 1955 and 1956, when the 

 catch contained a large percentage of fish older 

 than age 2 (June and Reintjes, 1959, 1960), the 

 mean catch per set was relatively high. Both 

 the mean catch per set and the average age were 

 low in the North Atlantic in 1957 and 1958. In 

 the Middle Atlantic both the average age and 

 the mean catch per set tended to decrease fi'om 

 June to September and then increase sharply 

 in October, while in the North Atlantic both 

 tended to increase from June to October. 



Except for the South Atlantic area, where 

 the disapiiearance of schools by midday limits 

 the number of sets, the mean number of sets 

 per day (Table 11) and the mean tons per set 

 (Table 12) were inversely correlated, implying 

 that fewer sets were necessary to load a vessel 

 in areas where the school biomass was large, that 

 schools became more numerous as their biomass 

 decreased, or that heavy fishing pressure tended 

 to keep school size small. 



Relative abundance also aiipears to influence 

 school biomass, but the relationship is not clear. 

 When the catch per vessel week, a measure of 



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