336 
Fishery Bulletin 99(2) 
even when the full range of M and faster growth were con- 
sidered, growth overfishing was not likely for the Chesa- 
peake Bay region fishery. 
Overall, yield-per-recruit curves showed that a sixfold 
increase in M resulted in a 50% decrease in yield for both 
growth rates (Figs. 1 and 4). As M increased, yield-per-re- 
cruit decreased. For a given M, yield-per-recruit increased 
to a maximum at an intermediate level of t c . Increases 
in yield slowed from 5-15 yr and decreased from maxima 
thereafter at older ages. In only one case (M= 0.02 and 
A'=0.105), yield-per-recruit increased with increased t c up 
to 20 yr. In all other cases, yield decreased for f c >20 yr, 
indicating that, beyond 20 yr, biomass was lost to natural 
mortality. 
Discussion 
Our results indicate that yield-per-recruit for black drum 
in the Chesapeake Bay region is below its maximum for 
all but the lowest values of M used in our simulations. For 
MAO. 04, current fishing mortality was below F MAX . Only 
when M=0.02 and f t .<15 does the upper bound of F CUR fall 
above F MAX . We discounted this case of extreme low M 
because of the unusually long lifetime that it predicts — 
some 200 years. Yield-per-recruit and economic efficiency 
could be maximized for black drum in Chesapeake Bay by 
decreasing t r to 5 years along with higher rates of fishing 
mortality. However, this may not be the most viable man- 
agement option for this species for several reasons. First, 
because the relation between yield-per-recruit and F is 
essentially asymptotic, harvesting black drum in the Bay 
at or near F MAX would require a huge increase in fishing 
effort, making harvest of this species economically inef- 
ficient, especially with the current low demand for these 
fish. Besides, benchmarks such as F MAX are no longer 
thought to provide a sustainable measure of long-term 
maximum yield from a fishei'y. Second, the current t c may 
reflect the mean age of migrating adults that are recruited 
to the fishery. If so, decreasing t c may not be possible 
because young fish may not undertake migration along 
the coast, and a decrease in mesh size may result in fail- 
ure of the net to “gill” the larger fish, with the result that 
catches would be diminished. 
Large reductions in biomass, especially of older fish, 
were shown in biomass modeling. Biomass decreases 
42-59%' under the most likely values of mortality (M=0.08, 
F C ur = 0-04; M=0.06, F CUR ~- 0.06, respectively) more than 
that of the unfished stock. Reductions in biomass (up to 
87%) are exacerbated when heavy fishing mortality is con- 
centrated on young fish. Concurrent with these reductions 
in biomass, is a rapid and dramatic loss of older fish from 
the stock. This juvenescence occurs quickly — t CRITICAl is 
reduced from 15 in the unexploited stock to 10 at F=0.02 
for M- 0.06, and from 13 to 10 at M- 0.08. At greater F, the 
decrease in t CRITICAL is even greater and the abundance of 
older fish diminishes further. 
Altogether these modeling results show no indication of 
growth overfishing in the Chesapeake Bay region where 
old fish are predominantly targeted. Moreover, it is diffi- 
cult to growth overfish a stock when fishing concentrates 
on capturing primarily older, larger fish. For example, 
black drum have already obtained 58% of their lifetime 
growth in length, and 22% of their lifetime weight when 
they first recruit to the Chesapeake Bay region at age 
six (Jones and Wells, 1998). By their mean age of capture 
in this region, they have obtained 90% of their lifetime 
growth in length and 51% in weight. Exploited cohorts 
have already surpassed their maximum growth by the 
time they enter the Bay region, and thereafter, natural 
mortality predominates. Cohort biomass has already de- 
clined from its optimum by the age fish enter the exploited 
stock in the Bay region. 
Although these modeling results show no indication of 
growth overfishing in Chesapeake Bay, they do indicate 
that black drum are vulnerable when heavy fishing is di- 
rected to young fish in the southern portion of their range 
along the U.S. East Coast. We chose a high level of F in the 
first five years of life to dramatically illustrate the effect 
of targeted fishing on small fish and the potential effects 
of bycatch from other fisheries. These simulations clearly 
indicate the importance of limiting fishing mortality in re- 
gions where young fish occur. Prior to 1989, black drum 
landed in the Florida east coast commercial fisheries aver- 
aged 320 mm (Murphy and Muller 2 ), and 80% of the catch 
was 4 yr or younger (Murphy and Taylor, 1989), raising 
the potential of growth overfishing at that time. Capture 
at this young age also raises concern for recruitment over- 
fishing, which our modeling does not address, especially 
when fish are targeted before they can reach sexual ma- 
turity (age 5). The potential for recruitment overfishing 
is minimal in areas, such as Chesapeake Bay, where the 
fishery targets older fish that have reproduced for many 
years before capture. Moreover, recent bans on gillnetting 
in Florida and other regulations on black drum fishing 
since 1989 should preclude recruitment overfishing and 
help preserve the stock. 
Models are typically used in management to regulate 
fishing mortality in order to obtain sustainable harvests 
from a stock. These regulations have historically resulted 
in harvests with large biomass that are valued in commer- 
cial fisheries. In contrast, recreational anglers are not as 
interested in obtaining maximum biomass as they are in 
catching fewer, but larger fish. Moreover, increased produc- 
tion of larger fish occurs when fishing mortality is below 
F MAX and when recruitment is high. Hence, in the black 
drum fishery, which is targeted by both commercial and 
recreational fishermen, management objectives are at cross 
purposes. The commercial fishery benefits when yields are 
maximized to the detriment of survival and growth for 
the trophy-size fish desired by recreational anglers. In the 
Chesapeake Bay region, fishing mortality is low and sup- 
ports the objectives of managing the recreational fishery. 
However, the most influential fishing mortality is on young 
fish and is not under the control of the Bay region manage- 
ment agencies, but is controlled by states farther south. 
The long-range migrations of the East Coast black 
drum stock argue for a coast-wide management strategy. 
Through our modeling, we have shown that fishing prac- 
tices in the Bay region have little impact on the production 
