310 
Fishery Bulletin 115(3) 
Simulation of 76 years under 
present-day management 
(ITQ system) 
l 
Simulation of 76 years under 
alternative management 
(addition of area management via 
closures to the ITQ system) 
1 
Annual data collected 
(performance metrics) 
(n=76) ^ 
Annual data collected 
(performance metrics) 
A. (n=76) 
Pair-wise comparisons of performance metrics via Wilcoxon signed-rank test 
I 
Identification of preferred option 
(simulations that result in improvement to the Atlantic surfclam stock 
and commercial fishery via improvement in performance metrics: 
density of the clam stock, number of clams per bushel, landings per unit 
effort [number of bushels per hour], number of 10’ squares visited to 
reach quota, distance traveled per fishing trip) 
Figure 6 
Diagram of the methods used to identify a preferred option to 
meet management objectives (i.e., improvement in the biomass of 
the Atlantic surfclam ( Spisula solidissima) stock and economic op- 
portunities of the commercial fishery in the Mid-Atlantic Bight). 
ITQ=individual transferable quota. 
by the dredge is increased from 0% to 20%, a higher 
percentage of simulations show significantly increased 
stock density and the degree of increase in stock den- 
sity was also larger (Table 5). The increase in stock 
density with an increase in incidental mortality can be 
explained by the fact that without closures (i.e., under 
present-day management), small clams are subjected 
to additional mortality over the entire stock. Because 
of the closure rules, the fishery is shifted from regions 
where mortality on small clams would be most sig- 
nificant to areas of lesser impact because fewer small 
clams reside there. A closed 10' square offers protection 
to the clams inside it until that 10' square is reopened 
to the fishery, and these 10' squares are characterized 
by a disproportionate number of small clams. As a con- 
sequence, the total mortality on small clams over the 
entire stock is reduced and stock density commensu- 
rately increases. 
Number of clams per bushel As the closure duration in- 
creased from 3 to 7 years, fewer clams were required to 
fill a bushel. Having fewer clams per bushel suggests 
that larger clams are landed under alternative manage- 
ment and that as the duration of the closure increased, 
the size of landed clams increased. The percentage of 
simulations that showed significantly more clams per 
bushel under present-day management reached 100% 
(Table 3) for all 5-year and 7-year closure durations. 
The number of clams per bushel was on av- 
erage 4% greater under present-day man- 
agement than under the 7-year closure du- 
ration (Fig. 7, Table 4). The increased clam 
size as the duration of the closure increased 
was not affected by an increase in inciden- 
tal mortality (Table 5). 
Landings per unit of effort As the size defin- 
ing a small clam decreased, a greater pro- 
portion of simulations had significant LPUE 
increases under the 5- and 7-year closure 
durations in comparison with LPUE under 
present-day management. The proportion 
of clams in the stock defined as small in- 
creased as the size defining a small clam de- 
creased. For example, as the definition of a 
small clam changed from 93-120 mm SL to 
80-120 mm SL, more clams in the popula- 
tion are defined as small because the clams 
between 92 and 80 mm SL are now added 
to the number of clams deemed to be small. 
The LPUE declines when the size definition 
increases from 80-120 mm SL to 93-120 
mm SL. The 10' squares with the highest 
clam density, which are now dominated by 
fewer small clams when the 93-120 mm SL 
definition is used, are being closed on the 
basis of the closure location rule (close 10' 
square with largest ratio of the number of 
small clams to the number of market-size 
clams). Thus, more clams are protected 
when the definition of a small clam is smaller (i.e., 80- 
120 mm SL) which leads to a larger number of clams 
in the stock when the 10' square reopens. 
All of the examined closure durations resulted in 
average increases of 6% in LPUE (Fig. 7, Table 4). The 
3-year closure duration resulted in 61% (Table 3) of 
simulations showing a significant increase in LPUE 
compared with that under present-day management. 
The 5-year closure duration had the highest average 
percentage of simulations that showed a significant 
increase in LPUE compared with LPUE under pres- 
ent-day management (range: 33-89%; average: 64%; 
Table 3). The 7-year closure duration had the lowest 
average percentage of simulations showing a signifi- 
cant increase in LPUE in comparison with that under 
present-day management (range: 33-56%; average: 
44%; Table 3). When additional incidental mortality is 
imposed, the effect of alternative management in in- 
creasing the LPUE is enhanced (Table 5). The 5-year 
closure duration resulted in an average 15% increase 
in LPUE, and 75% of simulations had significantly in- 
creased LPUE in comparison with that under present- 
day management (Table 5). 
Number of 10' squares fished The number of 10' 
squares fished during a year increased as the closure 
duration decreased (Fig. 7, Table 4) because captains 
are targeting 10' squares that recently opened after be- 
