FISHERY BULLETIN: VOL. 85, NO. 3 



Table 6. — Estimates of spawning stock size in thousands by age for Atlantic menhaden, 

 1954-81 seasons, at start of the fourth quarter of each fishing season. 



'Derived from 1 March 1955 estimates (see text). 



appeared in the fishery, it was assumed that some 

 representatives were still present in the popula- 

 tion at the beginning of quarter 4 (age X.75). Es- 

 timates of numbers present were obtained by a 

 forward calculation using the mortality estimates 

 of the previous interval obtained from the VPA's. 



not available, means from the nearest three year 

 classes were used. 



Estimates of egg production were obtained from 

 the expression used by Nelson et al. (1977), which 

 was derived from data of Higham and Nicholson 

 (1964): 



Estimates of Potential Egg 

 Production 



The age structure of the Atlantic menhaden 

 population varied substantially during the time 

 period under study. Therefore, an alternate 

 method of examining spawning stock (i.e., poten- 

 tial egg production) as used by Nelson et al. 

 (1977) was employed. 



Sizes at age X.75 for spawners derived from the 

 1955-78 year classes were calculated from the von 

 Bertalanffy growth parameters derived earlier 

 for the entire fishery (Table 3). However, because 

 of insufficient data, growth curves were not fitted 

 to the 1947-54 year classes, so observed mean 

 lengths at age during the fourth quarter were 

 used for the spawners derived from these year 

 classes. If the fourth quarter length at age was 



ln(£;) = 0.3149 + 0.0176L 



where, E = thousands of eggs produced per fe- 

 male, and 

 L = estimated fork length. 



This equation was used with estimated mean 

 length at age X.75 for fish 2 years and older. As- 

 suming a 50/50 sex ratio, potential egg production 

 by age by season was obtained by multiplying the 

 values per female by number of females at age 

 (Table 7). 



Estimates of Numbers of Recruits 



Estimates of the number of recruits for each 

 year class were obtained from the results of the 

 VPA's. The year class-size estimates for 1955-64 

 are from the mixed time-interval analyses and 



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