Kuykendall et al: A management strategy evaluation for Spisula solidissima 
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Table 5 
Evaluation of the model simulations in which closure location rule 1 was used to examine the influence of increased inci- 
dental mortality on the stock and commercial fishery of Atlantic surfclam ( Spisula solidissima) in the Mid-Atlantic Bight. 
Tabulated are the proportion of simulations where metrics used to evaluate the Atlantic surfclam population and the effect 
of area management on the commercial industry were significantly greater under alternative management with 0% or 20% 
incidental mortality with present-day abundance. Rule 1 mandates that the cell with the highest ratio of the number of 
small clams to the number of market-size clams is closed each year. Number of clams per bushel is not included because 
present-day management always has higher numbers of clams per bushel. There were 9 simulations per percentage. Any 
fraction over 0.11 (1 significant difference out of 9) is unlikely to occur by chance (exact binomial test: a=0.05; Conover, 
1980). Size of clams is given as shell length (SL) in millimeters, closure duration is measured in years, and LPUE means 
landings per unit of effort. 
Definition of a small clam 
104 mm SL 93 mm SL 80 mm SL 64 mm SL 
Closure duration (yr) 
357357357357 
Stock density 
0% incidental mortality 
0.44 
0.33 
0.56 
0.44 
0.67 
0.44 
0.56 
0.56 
0.44 
0.22 
0.33 
0.33 
20% incidental mortality 
0.56 
0.78 
0.78 
0.44 
0.78 
0.78 
0.22 
0.56 
0.67 
0.22 
0.56 
0.56 
LPUE 
0% incidental mortality 
0.44 
0.33 
0.56 
0.67 
0.56 
0.44 
0.78 
0.78 
0.33 
0.56 
0.89 
0.44 
20% incidental mortality 
0.67 
0.78 
0.56 
0.67 
0.89 
0.78 
0.44 
0.67 
0.56 
0.22 
0.67 
0.78 
Number of 10' squares fished 
0% incidental mortality 
0.22 
0.00 
0.11 
0.11 
0.00 
0.00 
0.11 
0.00 
0.00 
0.33 
0.00 
0.00 
20% incidental mortality 
0.22 
0.00 
0.11 
0.00 
0.00 
0.11 
0.11 
0.11 
0.11 
0.11 
0.00 
0.00 
Total distance traveled 
0% incidental mortality 
0.33 
0.56 
0.78 
0.11 
0.44 
0.67 
0.33 
0.44 
0.44 
0.22 
0.44 
0.44 
20% incidental mortality 
0.11 
0.33 
0.56 
0.56 
0.22 
0.44 
0.33 
0.44 
0.44 
0.33 
0.22 
0.44 
average proportion of increase in LPUE was improved. 
The 5-year closure duration showed the most improve- 
ment with LPUE increased by an average of 12% (com- 
pared with 8% without additional mortality). 
Number of 10' squares fished As the duration of a 
closure increased, the percentage of simulations with 
significantly more 10' squares fished during the year 
decreased. The average percentage of increase in 10' 
squares fished under present-day management and 
over all alternative management strategies was only 
3% and 4% respectively, however (Fig. 8, Table 6). The 
high percentage of simulations that showed no signifi- 
cant difference between present-day and any closure 
duration (66%, 75%, and 59% for the 3-, 5-, and 7-year 
closure durations; Table 7), accompanied by the small 
percent changes, indicate little effect of any alternative 
management strategy in changing the number of 10' 
squares visited during fishing. As incidental mortality 
increased, slightly fewer 10' are visited with increas- 
ing closure duration (Table 8). The percentage of cases 
where significantly fewer 10' squares were visited un- 
der alternative management increased; however, the 
average percentage of increases of 10' squares visited 
under present-day or alternative management were 
still 5% or less (Fig. 8, Table 6). 
Distance traveled per fishing trip The distance traveled 
per fishing trip increased significantly in 94% of simu- 
lations for the 3-year closure duration and in 90% of 
simulations for the 5- and 7-year closure durations (Ta- 
ble 7). The average percent increase for each of the clo- 
sure durations was only 5%, however (Fig. 8, Table 6). 
An increase in incidental mortality resulted in a lower 
percentage of simulations with increased distance trav- 
eled during fishing trips (averages of 41%, 61%, and 
64% for the 3-, 5-, and 7-year closure durations; Table 
8). The percentage of increase was less than 4% for all 
closure durations. 
Discussion 
Perspective 
The goal of this study was to use an MSE to investigate 
possible options that could enhance productivity in the 
Atlantic surfclam stock without unjustifiably limiting 
the fishery through undesirable economic impacts. An 
MSE allows an evaluation of alternative management 
options on the basis of performance metrics that are 
understood by and valuable to both stakeholders and 
fishery managers. The range contraction of Atlantic 
