AHRENHOLZ ET AL.: ATLANTIC MKNUADEN POPULATION AND FISHERY 



clusters of yield values: high abundance gears 

 (1955-62), low abundance (high Fp^p) years of 

 1963-68 (with the exception of 1967), and years of 

 low to moderate population size (1969-79). These 

 clusters are less distinct when yield is measured 

 in numbers of fish rather than biomass. A 



Graham-Schaefer curve, fitted to fishing mortal- 

 ity and yield in numbers of fish, resulted in a 

 numbers MSY of 2.383 billion fish at an optimum 

 Fpop = 0.522 (Fig. 14). Each year's yield in num- 

 bers as compared to biomass (Fig. 13, 14) suggests 

 that the fishery in the late 1970's was not produc- 



i ^ TY~^ t p 1 :8 — % — i^ — 1.1 ^ 1.2 



POPULATION F 



Figure 13. — Catch of Atlantic menhaden in thousands of metric tons plotted against 

 estimates of population F for years 19-5.5-79. Curve a is the result of fitting the Pella- 

 Tomlinson's ( 1969) generalized yield function with adjustments for nonequilibrium con- 

 ditions iPRODFIT, Fox 1 1975)1. Curve b is a nonlinear least squares fit of the parabolic 

 (Graham-Schaefer) production model. 



X 

 CO 



u. 

 O 



CO 



z 

 o 



m 



z 



I 

 o 



< 

 o 



POPULATION F 



Figure 14.— Catch of Atlantic menhaden in billions offish against estimates 

 of population F for years 1955-79. The curve is the result of a nonlinear least 

 squares fit of the parabolic (Graham-Schaefer) production model. 



587 



