304 
Fishery Bulletin 115(3) 
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Figure 3 
(A) Map showing the location of home ports and a representation of the model do- 
main outlined for this study of management strategy evaluation for Atlantic surf- 
clam ( Spisula solidissima ) in the Mid-Atlantic Bight. (B) Model domain with ports 
(black squares), fishable areas (white squares), unfishable areas (light gray squares), 
and land (dark gray squares). Each cell in the domain has a resolution of IQ'xlO'. 
The domain contains 52 10' squares available to the fishery (white squares). Dis- 
tance represents distances along the x and y axis of ten-minute squares in the grid. 
for 10' squares that were fished. The memory of LPUE 
for a 10' square fished during a trip is updated after 
each trip. Over time a captain’s memory of the entire 
domain degrades as the stock changes because the 
captain has up-to-date information only for recently 
fished 10' squares. Each captain has a skill level that 
can range from 1 to 10 in the model — a level that de- 
termines the amount of time the dredge is actively 
fishing with 10 representing 100%. All captains in this 
study had a skill level of 10. See Powell et al. (2015) 
for a more detailed description of “captain memory de- 
velopment” and skill levels. 
Each simulation spans a total of 201 years. The time 
step is given in days and certain fishing activities are 
time-stepped in hours, and data for evaluation of per- 
formance metrics are collected annually. Model days 
are converted to calendar dates to allow for seasonal 
variability in weather and fishing behaviors (e.g., fewer 
trips during winter months). No fishing occurs in the 
first 100 years of each simulation to allow the Atlantic 
surfclam population to reach equilibrium with specified 
characteristics, such as abundance and distribution of 
individuals that are based on larval survival. After this 
period of time, the population is near carrying capac- 
ity and is characterized by a locally patchy distribu- 
tion with regional characteristics consistent with the 
latitudinal and cross-shelf temperature gradients. The 
next 25 years represents historical fishing. During this 
time, a captain’s memories of stock distribution and 
LPUE develops and the stock is fished down to a de- 
sired specified level. Area management is imposed in 
year 126 and the final 76 years are used to evaluate 
the area management option (i.e. the combination of 
closure location rule and closure duration used) in rela- 
tion to present-day management. 
Three initial stock distributions ranging from dense 
to sparse levels of patchiness were specified to cover a 
range in stock patchiness. Patchiness was established 
by assigning new recruits to each 10' square by using 
a negative binomial random distribution that produced 
distinctive variance in the abundance of clams in each 
10' square relative to the mean abundance for all 10' 
squares. Variation in patchiness of the distribution is 
included in this study as a sensitivity analysis with a 
range that is typical of bivalve populations and consis- 
tent with Northeast Fisheries Science Center Atlantic 
surfclam and ocean quahog ( Arctica islandica) survey 
data. An Allee effect was not included; population den- 
sities are assumed not to limit fertilization efficiency. 
Recruitment is an annual event. The recruitment rate 
is set by a broodstock-recruitment relationship (Pow- 
ell et al., 2015) that results in levels of postsettlement 
abundance that are representative of present-day 
abundance that is based on data from the Northeast 
Fisheries Science Center 2011 Atlantic surfclam and 
ocean quahog survey. 
