AHRENHOLZ ET AL.: ATLANTIC MENHADEN POPULATION AND FISHERY 



9r 



(r 

 m 



2 



01 



O 



o 



AGE IN YEARS 



Figure 10. — VPA (virtual population analysis) estimates of numbers at age present in the 

 Atlantic menhaden population for the 1955 year class for three levels of natural mortality 

 (lower left), and natural logarithms of these same numbers at age (upper right). 



X 



CO 



tr 

 o 



LU 



tr 



a. 

 ui 

 m 



3 

 Z 



18 



16 



14 



12 



10 



, Mr 0.55 

 U-- 0.45 

 M= 0.35 



J — I — I — I — I — I — I — I — I — I r I 'y^i. I I i I I III' 



1956 58 60 62 64 66 68 70 72 74 76^ 78 



YEAR CLASS 



Figure 11. — Annual VPA (virtual population analysis) estimates of numbers of Atlantic 

 menhaden recruits at age 1 for three levels of natural mortality. 



tained from the quarterly VPA series. These esti- 

 mates were rearranged to correspond to fishing 

 seasons (Table 6). There were no estimates for 

 numbers at age landed in the 1954 North Caro- 

 lina fall fishery. Hence, the parental spawning 

 stock for the 1955 year class was obtained by 

 using 1955 estimates for age X.O and back- 



calculating numbers at age to the beginning of 

 the 1954 fourth quarter (age (X - 1).75) with 

 mean fourth quarter survival rates at age for fish- 

 ing years 1955-57. An additional adjustment was 

 made to complete the estimates of spawning stock 

 size. If an age group was represented during quar- 

 ters 1-3 but not in quarter 4 of the last year it 



583 



