Barbieri et al.: Yield-per-recruit analysis for Micropogonias undulatus 
643 
6.7, 6.1, and 5.6 years, respectively. ForL^ = 645 mm 
and the estimated level of l c for the period 1979-81 
(177 mm, corresponding to t c - 1), P ' = 0.72, i.e., on 
the average, 72% of their potential growth still 
remained when Atlantic croaker in North Carolina 
entered the exploited phase at age 1 during the 
period 1979-81. For alternative values of t c = 2-5 
years, values of P g were 0.59, 0.49, 0.39, and 0.33, 
respectively. 
Discussion 
Our modeling results indicate that, for the range of 
M and F used in simulations, yield-per-recruit of 
Atlantic croaker in the lower Chesapeake Bay could 
be maximized by a management strategy that incor- 
porates early age at first capture (£ c =l) and high rates 
of fishing mortality (F=2.Q). However, the analysis 
for Chesapeake Bay also showed this is probably not 
the most efficient management option for this spe- 
cies. Because of the essentially asymptotic relation 
between yield-per-recruit and F, harvesting Atlantic 
croaker at or near their maximum potential yield (i.e. 
at F max ) would require a disproportionate increase 
in fishing mortality making it an economically inef- 
ficient management option. In addition, given the 
multispecies nature of the main fisheries for Atlan- 
tic croaker in Chesapeake Bay (Austin, 1987; Chit- 
tenden, 1991), raising current levels of F would 
greatly increase overall rates of exploitation and 
probably interfere with management of other spe- 
cies such as weakfish, Cynoscion regalis, and spot, 
Leiostomus xanthurus. 
Decreasing the current level of t for Atlantic 
croaker in Chesapeake Bay would not be recom- 
mended for two reasons. First, for the range of M 
used in simulations, gains in yield-per-recruit from 
t = 2 to t = 1 were relatively small at F CUR . Second, 
because of the magnitude of the scrap catch of At- 
lantic croaker in Chesapeake Bay (Mercer 1 ), it is 
likely that this species is already entering the ex- 
ploited phase at age 1 or younger. The current esti- 
mate of t (t c = 2; Barbieri et al., 1994a) may be an 
overestimate because it was based on arbitrarily 
defined commercial market grades instead of over- 
all catches — including the scrap. Because the mar- 
ket accepts only fish above a certain size, a reduc- 
tion in mesh sizes to attempt 
to increase the proportion of 
age-1 Atlantic croaker in the 
catches would probably only 
increase the number of fish 
sold as scrap and have little 
or no effect on commercial 
market grades. 
Nevertheless, the analysis 
showed no indication that 
fully recruited Atlantic croaker 
in Chesapeake Bay are being 
growth-overfished (i.e. that 
the fish were being caught 
before they had a chance to 
grow to their ideal size). 
Yield-per-recruit modeling 
results and estimated values 
of F cur indicated that, over 
a likely range of M, current 
levels of harvest are below 
the levels at F and, under 
most scenarios, at or below the 
levels atF 0 r In addition, yield- 
per-recruit curves showed no 
signs of decrease at higher lev- 
els of F, even if M is as low as 
0.20. This pattern suggests 
that stocks of Atlantic croaker 
in the Chesapeake Bay region 
show the same great biologi- 
F 
Figure 4 
Curves of yield-per-recruit on fishing mortality (F) for Atlantic croaker, Micropogonias 
undulatus , in North Carolina (period 1979-81) estimated for mean age-at-first-capture 
(t c ) = 1 and natural mortality (M) = 0.20-0.35. F 0 1 = the level of F 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. 
