Sturdivant and Clark: Effects of Callinectes sapidus behavior on the efficacy of crab pots for estimating population abundance 
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Discussion 
Intraspecific blue crab interactions did not affect crab 
trap efficacy, and although 52% of the observed interac- 
tions between crabs were aggressive or agonistic, none 
prevented entry or resulted in an exit from the pots. 
In situ, the presence of crabs in pots did not affect the 
catch rate. These findings are contrary to those from 
other studies where the relationship between crusta- 
cean behavior and catch rates was observed (Jury et 
ah, 2001; Barber and Cobb, 2009). Jury et al. (2001) 
observed large American lobsters actively defending 
and preventing conspecifics from entering pots and 
accessing the bait, and Barber and Cobb (2009) observed 
Dungeness crabs guarding the entrance to pots and 
restricting entrance to conspecifics. Clark et al. (2000) 
showed that at high blue crab density, foraging success 
is hampered by intraspecific aggression; however, the 
caveat from our study is that feeding does not occur in 
crab pots. In American lobster pots the bait hangs down 
between the entrances to the pot. American lobsters 
can enter the pot only by coming in close proximity to 
a lobster feeding on the bait. Observations from work 
by Jury et al. (2001) described lobsters wielding the 
bait and fending off interested conspecifics. In standard 
commercial crab pots, unlike lobster traps, the bait is 
placed in a wire cage inside the pot and is inaccessible. 
The unattainable bait may change the nature of the 
intraspecific behavioral dynamics of crabs in the pres- 
ence of food. In other studies showing that aggressive 
behavior impacts catch rate, the aggressive behavior 
may have been related to the defense of a habitat or 
territory. Barber and Cobb (2009) observed Dungeness 
crabs guarding the entrance to pots and not the bait. 
We found no evidence in the literature that blue crabs 
guard specific habitats or exhibit spatial fidelity. Male 
crabs, in tagging experiments where a similar size and 
molt stage were used, ranged widely, meandering on 
scales of 50 to 100 meters for several hours to days, but 
sometimes moving on a fairly constant course at rates 
exceeding 300 m/h (Wolcott and Hines, 1996). 
Blue crabs may have been using the pots as a ref- 
uge from predators rather than entering them to feed. 
Blue crabs have been found in higher abundance in 
structured, woody debris (Everett and Ruiz, 1993) and 
sea grass (Eggleston et al., 1998) than in unstructured 
habitat. The design of the experiment is such that pots 
were a structured habitat relative to the surrounding 
environment. The crabs may have entered the pots in 
response to their value as structure. As further evi- 
dence that blue crabs may use pots for the structure 
that they provide, crabs have been found in unbaited 
pots (Guillory, 1993). These results may indicate a pot 
design by species interaction is important in the ef- 
ficacy of pots. 
Although intraspecific interactions were not observed 
or quantified to have an effect on catch or escape rates, 
there was a significant effect of depth on catch rate 
in our field experiments. Blue crabs caught at the 3 
m depth were significantly smaller and less abundant 
than crabs caught at the 1 and 2 m depths. Studies 
have shown the importance of shallow water as ref- 
uge habitat for juvenile fishes and crustaceans in this 
system (Ruiz et ah, 1993). The shallow waters are as- 
sociated with increased abundance and decreased risk 
of predation for smaller organisms (Ruiz et al., 1993; 
Clark et al., 2000). In our study, the increased catch 
rate of smaller crabs at deeper “riskier” depths may 
be a function of an increased risk of predation; the 
smaller crabs used the pots as a refuge, which allowed 
them to exploit deeper depths. Significantly fewer blue 
crabs were caught at the 3-m depth than at the 1- and 
2-m depths. It is possible that the benthic secondary- 
production of the 1- and 2-m depths in CHB exceeds 
that of the 3-m depth enough to attract higher numbers 
of and larger crabs. 
In our field and mesocosm experiments blue crabs es- 
caped at high percentages of 41% and 85%, respectively. 
The field observations may actually underestimate and 
the mesocosm experiment may overestimate escape 
percentages. The percentage of crabs that escaped in 
the field experiment was calculated from tagged crabs 
placed in the pots. These point observations do not ac- 
count for blue crabs that entered and exited before the 
pot was sampled. In the mesocosm study, we were un- 
successful in our attempts to individually identify crabs. 
We had no method of determining the number of times 
an individual crab entered and exited the pot, and this 
may have artificially inflated our observed escape rate. 
We observed crabs entering and exiting the kitchen 
section of the pot with relative ease. Most crabs only 
needed a few minutes to find the exit, and some swam 
in through one side and directly out another opening. It 
is important to note that once crabs entered the parlor, 
the rate of escape decreased dramatically; crab escape 
from the parlor was only 2%. Most crabs that entered 
the parlor explored for a few minutes before becoming 
inactive. However, one particularly determined crab 
crawled around the parlor for several hours before es- 
caping into the kitchen. It is possible that blue crab 
population estimates that use pots should only rely 
on parlor captures as an accurate measure of relative 
crab abundance. The escape rate from the parlor was 
almost zero, but the ease and high escape rate from the 
kitchen will undeniably bias CPUE results if included 
in population estimates. 
The escape rate of crustaceans from pots is a rec- 
ognized factor in the trap fishery (Bennet, 1974). Tra- 
ditionally, escape rates for blue crabs have focused on 
mechanisms for excluding sublegal crabs from the catch 
and on inferences from the impacts of derelict pots 
(Guillory, 1993; 1998). Jury et al. (2001) found that 
American lobster traps retained only 6% of their po- 
tential catch. In previous studies, the range of escape 
rate for lobsters and crabs was approximately 60-70% 
(Muir et al., 1984; Karnofsky and Price, 1989). High 
and Worlund (1979) found that an average of 80% of 
tagged king crabs ( Paralithodes camtschaticus) escaped 
from pots. They identified a number of factors that im- 
pacted escape rate, such as presence of bait, soak time, 
