JUNE: ATLANTIC MENHADEN GROUPINGS 



SIZE OF SUMMER SCHOOLS IN 



RELATION TO APPARENT 



ABUNDANCE OF THE FISH 



It was shown earlier that the mean single- 

 school summer catch declined over the 8-year 

 period in the two northern areas and fluctuated 

 randomly in the two southern areas. To deter- 

 mine if these trends were an artifact of sampling 

 or actually reflected variations in apparent 

 abundance of the summer stock in the respective 

 areas, I plotted the average catch per vessel week 

 given by Nicholson (1971b) against the mean 

 single-school summer catch in the corresponding 

 season. There was good agreement between the 

 two estimates in every area (Figure 12), but 

 the relationship was closer for the South At- 

 lantic and Middle Atlantic Areas than for the 



15 — 



I 10 



North Atlonfic Areo 



Chesapeake Bay Area 



Middle Atlantic Area 



South Atlantic Area 



J L 



10 



20 25 10 15 20 



Colch per Single-School Set (MT) 



25 



500 



400 



300 - 



I- 



z 



» 100 



300 - 



10 IS 



20 25 10 IS 20 2S 



Cotch per Single-School Set (MT) 



Figure 12. — Relationship between the purse-seine catch 

 of Atlantic menhaden per vessel week and the mean 

 single-school summer catch in the major statistical areas, 

 1955-62. 



Figure 13. — Relationship between the estimated number 

 of purse-seine sets for Atlantic menhaden and the mean 

 single-school summer catch in the major statistical areas, 

 1955-62. 



Chesapeake Bay and North Atlantic Areas. 

 The correlation coefiicient for the South At- 

 lantic Area is significant at the 1% level and, 

 that for the Middle Atlantic Area at the 5% 

 level. Although the coefficients for the Ches- 

 apeake Bay and North Atlantic Areas are pos- 

 itive, neither differs significantly from 0. These 

 findings indicate that summer schools became 

 smaller as stock abundance in a given area 

 decreased. 



The relation between school number and 

 school size is also of interest in assessing changes 

 in stock abundance. A plot of the seasonal num- 

 ber of successful purse-seine sets (a measure 

 of school density) given by Nicholson (1971b) 

 on the corresponding mean single-school summer 

 catch (Figure 13) shows a wide scattering of 

 points within areas and considerable variability 

 between areas. The correlation coefficient is pos- 

 itive for the Chesapeake Bay and North Atlan- 

 tic Areas, negative for the Middle Atlantic Area, 

 and about for the South Atlantic Area, with 

 only that for the North Atlantic Area having 



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