Barbieri et al.: Yield-per-recruit analysis for Micropogonias undulatus 
641 
F 
Figure 2 
Curves of yield-per-recruit on fishing mortality (F) for Atlantic croaker, Micropogonias 
undulatus, in the lower Chesapeake Bay (period 1988-91) estimated for mean age-at- 
first-capture ( t ) = 2 and natural mortality (M) = 0.20-0.35. F 0 7 = the level ofF at which 
the marginal increase in yield-per-recruit due to a small increase in F is 10% of the 
marginal yield-per-recruit in a lightly exploited fishery; F CUR = the estimated current 
levels of fishing mortality. 
the level of F 0 l (Fig. 2; Table 3). For M = 0.20, F CUR 
is higher than F () p indicating that, although it pro- 
duces slightly higher yield values, current fishing 
mortality is not at its most economically efficient 
level. For example, for t c = 1 and t c = 2, over 90% of 
the yield obtained at F CUR can be achieved by lower- 
ing fishing mortality to the level of F 0 r For M = 0.25, 
both F ci;r andF 0 j equal 0.35, indicating that, although 
below the maximum potential yield-per-recruit, esti- 
mated current levels of harvest probably correspond to 
the most efficient level of F. In contrast, if M ranges 
from 0.30 to 0.35, F 0 1 is higher than F CUR (Table 3), 
suggesting there would still be room to increase yield 
efficiently with increases inF. However, at these higher 
levels of M, increases in F necessary to achieve the 
yields at F 0 , may be unrealistically high (Table 3). 
Values of t CR1TIC estimated with different values 
of M were relatively low for Atlantic croaker in Chesa- 
peake Bay. For M equal to 0.20, 0.25, 0.30, and 0.35, 
values of t CRITIC were 1.9, 1.4, 1.0, and 0.6 years, re- 
spectively. These values indicate that, for the range 
of M considered herein, maximum theoretical cohort 
biomass in the absence of fishing would be achieved 
before Atlantic croaker reach age 2 (years). 
Table 3 
Estimated value of current levels of fishing mortality (F CUR ) 
and level of fishing mortality at which the marginal in- 
crease in yield-per-recruit due to a small increase in F is 
10% of the marginal yield-per-recruit in a lightly exploited 
fishery ( F 0 , ) for Atlantic croaker, Micropogonias undulatus, 
in the Chesapeake Bay region for a range of fishing mor- 
tality (Ml = 0.20-0.35, and the percent increase or decrease 
in F cur necessary to make it equal to F 01 . 
M 
F 
r CUR 
F). i 
% Difference 
0.20 
0.40 
0.27 
-48 
0.25 
0.35 
0.35 
0 
0.30 
0.30 
0.45 
+50 
0.35 
0.25 
0.64 
+ 156 
Estimated values of P g for Atlantic croaker in 
Chesapeake Bay were also relatively low. For = 
3 12 mm, and the current estimated level of l c (265 mm, 
corresponding to t c = 2), P g = 0.15, i.e., on the aver- 
age, only 15% of their potential growth still remains 
when Atlantic croaker in Chesapeake Bay enter the 
exploited phase at age 2. For alternative values of t 
