Kuykendall et al.: A management strategy evaluation for Spisula solidissima 
311 
Table 2 
Summary statistics for average proportion differences for the number of clams per bushel and landings per unit of effort 
(LPUE), measured as the number of bushels fished per hour and given as examples of the results for the model that used 
the 4-year closure duration in an evaluation of management strategy for the Atlantic surfclam ( Spisula solidissima ) in the 
Mid-Atlantic Bight. Comparison can be made with data in Table 6. Size of clams is given as shell length (SL) in millimeters, 
and closure duration is measured in years. N is the number of simulations where a significant difference exists between 
the performance metric under present-day or alternative management at present-day abundance. The maximum N is 9. 
Definition of a small clam 
Number of clams per bushel 
Present management N 
X 2 
Alternative management N 
X 2 
LPUE 
Present management 
N 
X 2 
Alternative management N 
X 2 
104 mm SL 
93 mm SL 
80 mm SL 
64 mm SL 
Closure duration (yr) 
3 
4 
5 
7 
3 
4 
5 
7 
3 
4 
5 
7 
3 
4 
5 
7 
5 
9 
9 
9 
2 
9 
9 
9 
2 
5 
9 
9 
2 
3 
9 
9 
0.01 
0.02 
0.03 
0.04 
0.01 
0.02 
0.03 
0.04 
0.01 
0.01 
0.02 
0.04 
0.01 
0.01 
0.01 
0.03 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
1 
1 
1 
0 
1 
0 
1 
0 
0 
1 
1 
0 
0 
0 
1 
- 
0.03 
0.04 
0.05 
- 
0.04 
- 
0.02 
- 
- 
0.05 
0.04 
- 
- 
- 
0.02 
4 
7 
3 
5 
6 
5 
7 
4 
7 
9 
7 
3 
5 
5 
8 
4 
0.06 
0.09 
0.05 
0.06 
0.07 
0.07 
0.08 
0.12 
0.05 
0.05 
0.08 
0.12 
0.07 
0.05 
0.07 
0.09 
ing closed for some duration of years. A 10' square that 
has been closed for a longer duration will result in the 
landing of larger clams and have a higher stock den- 
sity, and therefore LPUE will be higher and lead to the 
vessels targeting these 10' squares for a larger number 
of trips. Consequently, fewer 10' squares will be vis- 
ited to fill quotas. Increasing the incidental mortality 
imposed on clams that remain after dredging resulted 
in a larger percentage of simulations with significantly 
fewer 10' squares fished during the year. Increased in- 
cidental mortality also caused larger percent decreases 
in the number of 10' squares visited under alternative 
management. 
Distance traveled per fishing trip In an average of 24% 
(range: 11-33%; Table 3) of 3-year closure simulations, 
the distance traveled to the fishing ground increased 
significantly, with an average increase in distance 
over all simulations of 3% (Fig. 7, Table 4). The 5-year 
closure duration also resulted in an average increase 
in distance traveled of 3% (Fig. 7, Table 4), but 47% 
(range: 44-56%; Table 3) of simulations showed signifi- 
cantly increased distance traveled under area manage- 
ment. The 7-year closure duration demonstrated the 
highest percentage of cases having significantly greater 
distances traveled (average: 58%; Table 3). Accordingly, 
the 7-year closure duration also resulted in the larg- 
est average percent increase in distance traveled (8%; 
Fig. 7, Table 4). As closure duration increases, some of 
the 10' squares that are closed are close to the ports; 
the fishery would target these otherwise. Thus travel 
distance increases. A longer closure duration results 
in more 10' squares close to the ports being closed: 
distance traveled must increase commensurately. The 
average percent increase in distance traveled was 4% 
(Fig. 7, Table 4) for all closure durations. When inci- 
dental mortality imposed on clams that remain after 
dredging was increased, the percentage of simulations 
that had significantly greater distances traveled under 
area management decreased (Table 5). 
Closure location based on rule 2: the number of small 
clams per square meter 
Stock density The 3-year closure duration resulted 
in an average increase of 4% in stock density (Fig. 8, 
Table 6), but an average of only 36% (range: 33-44%; 
Table 7 of simulations showed significantly increased 
stock density compared with that under present-day 
management. The 5-year closure duration resulted in 
an average increase in stock density of 4% (Fig. 8). 
The 5-year closure duration also had the highest av- 
erage percentage of simulations that showed a signifi- 
cant stock density increase compared to present-day 
management (range: 33-67%; average: 50%; Table 7). 
The 7-year closure duration resulted in a 5% aver- 
age increase in stock density (Fig. 8). On average, the 
7-year closure duration showed significant increases 
in stock density in only 39% (range 0-56%; Table 7) 
of the simulations in comparison with present-day 
management. An increase in incidental mortality en- 
hances the effect of alternative management (Table 8 
