Kuykendall et a!.: A management strategy evaluation for Spisula solidissima 
321 
important economic gain in reducing the cost of fuel 
relative to the value of the landed clams. 
The number of 10' squares visited during fishing 
increases significantly in an average of 7% of simu- 
lations over all closure durations and definitions of a 
small clam in comparison with an average of 49% of 
simulations under present-day management. A reduc- 
tion in the number of 10 ' squares visited suggests that 
captains (who choose a fishing location on the basis of 
highest catch rate, but who are limited in the sum- 
mer by the 36-h time constraint) target the recently 
opened 10' squares. The distance traveled during fish- 
ing also increases significantly in up to 58% of simula- 
tions. An increase in distance traveled occurs in some 
cases because the closed 10 ' squares are close to the 
home ports and require that captains steam farther 
away from port to fish. In addition, some of the 10' 
squares recently opened are farther from home port, 
but the higher LPUE makes travel to them economi- 
cally advantageous. Reduced distance is often preferred 
because reduced steaming time reduces operational 
costs, thus increasing profit margins, unless the addi- 
tional cost of steaming is compensated by a reduction 
in other trip costs. This would be the case if LPUE also 
increases, as it does in these simulations. If a vessel 
steams for 8 h at a speed of 5 m/s, a 4% increase in 
distance traveled would result in approximately an ad- 
ditional 7.4 km (4 nautical miles), which would allow 
fishing of 1 additional 10' square away from home port 
without substantial additional costs if that 10' square 
yielded a higher LPUE. 
Influence of control rules 
The criterion used to select a closure location is im- 
portant for the success of management in offering en- 
hanced stock densities and additional economic oppor- 
tunity to the industry. Two closure location rules were 
investigated that represent end-members [extreme op- 
tions] of a range of choices for a control rule; one places 
importance on the number of small clams in relation 
to the number of market-size clams (rule 1) and the 
other places importance on the density of small clams 
in an area (rule 2). Optimizing area management would 
require evaluation of the influence of combined rules, 
such as the 10 ' square with the highest density of 
small clams among the 25% of 10' squares with the 
highest proportion of small clams. A comparison of the 
end-member options, however, shows that stock density 
increased in a higher percentage of simulations under 
closure location rule 1, the proportional rule, in com- 
parison with closure location rule 2 and present-day 
management. Average percent increases in stock densi- 
ty are also higher under closure location rule 1. Accord- 
ingly, an increase in stock density is seen when the 10 ' 
square with the greatest number of small clams in com- 
parison with the number of market-size clams is closed 
to fishing for some duration of years. Both closure loca- 
tion rules resulted in an average of 64% of simulations 
having increased LPUE when compared with present- 
day management (i.e., no closures). A higher average 
percentage of increase resulted with closure location 
rule 2. However, closure location rule 1 resulted in an 
increase in LPUE as the closure duration increased, as 
opposed to a gradual decline seen when using closure 
location rule 2. An increase in LPUE when high impor- 
tance is placed on the presence of small clams suggests 
that protecting small clams is a key factor in offering 
more economic opportunity to the fishing industry. 
When the choice of closure location is based on the 
ratio of the number of small clams to the number of 
market-size clams (rule 1), the percentage of simula- 
tions where fewer 10' squares were fished was much 
higher. This result suggests that these 10' squares re- 
tain high catch rates longer under closure location rule 
1. When the closure location is based on rule 1, transit 
distance was increased in substantially fewer simu- 
lations in comparison with closure location based on 
closure location rule 2 or present-day management. A 
decrease in distance traveled in a comparison of closure 
location rules 1 and 2 suggests that when importance 
is placed on the ratio of the number of small clams to 
the number of market-size clams, even though the 10' 
squares closed may be near home ports, once open they 
provide improved catch rates more often than if the 
location of the closed 10' square was selected on the 
basis of abundance of small clams alone. This outcome 
is consistent with the more persistent targeting of these 
10' squares under closure location rule 1. 
The average percent increase in the number of clams 
per bushel — a metric directly related to the size of land- 
ed clams — is essentially equal for both closure location 
rules. Because some of the performance metrics (e.g., 
number of clams per bushel) showed little difference 
between the 2 closure rules, a third option of combining 
the 2 rules might offer additional benefits for the com- 
mercial fishery. However, on the basis of the percentage 
of simulations that indicated improvement of the stock 
and the margins of increase, the 5-year closure dura- 
tion under closure location rule 1, which relies on the 
proportion of small clams to identify a 10' square to 
close, offers the most benefit for the stock and therefore 
is identified as the preferred option. Of greatest impor- 
tance is the increase in whole-stock density that occurs 
while landings are retained near levels of the present 
day. In addition, based on the percentage of simulations 
that indicate additional economic opportunities offered 
to the commercial fishery, the 5-year closure duration 
under closure location rale 1 offers the most benefit to 
the stock and thus again is identified as the preferred 
option. 
Influence of incidental mortality 
Little information exists about the incidental mor- 
tality of clams encountered by the dredge but that 
remain on the seafloor. NEFSC 2 assumes 12% in- 
cidental mortality, but this assumption is based on 
very little data and primarily on the outcome for 
market-size clams (Meyer et ah, 1981), few of which 
