Abstract — Crab traps have been used 
extensively in studies on the popula- 
tion dynamics of blue crabs to provide 
estimates of catch per unit of effort; 
however, these estimates have been 
determined without adequate consid- 
eration of escape rates. We examined 
the ability of the blue crab ( Callinectes 
sapidus ) to escape crab pots and the 
possibility that intraspecific crab 
interactions have an effect on catch 
rates. Approximately 85% of crabs 
that entered a pot escaped, and 83% of 
crabs escaped from the bait chamber 
(kitchen). Blue crabs exhibited few 
aggressive behavioral interactions in 
and around the crab pot and were 
documented to move freely in and out 
of the pot. Both the mean number 
and size of crabs caught were sig- 
nificantly smaller at deeper depths. 
Results from this study show that 
current estimates of catch per unit of 
effort may be biased given the high 
escape rate of blue crabs documented 
in this study. The results of this paper 
provide a mechanistic view of trap 
efficacy, and reveal crab behavior in 
and around commercial crab pots. 
Manuscript submitted 15 December 2009. 
Manuscript accepted 18 October 2010. 
Fish. Bull. 109:48-55 (2011). 
The views and opinions expressed 
or implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National Marine 
Fisheries Service, NOAA. 
An evaluation of the effects 
of blue crab ( Callinectes sapidus) 
behavior on the efficacy of crab pots 
as a tool for estimating population abundance 
S. Kersey Sturdivant (contact author ) 1 
Kelton L. Clark 2 
Email address for contact author: kersey@vims.edu 
1 Virginia Institute of Marine Science 
College of William & Mary 
P.O. Box 1346 
Gloucester Pt., Virginia 23062 
2 Morgan State University 
Estuarine Research Center 
10545 Mackall Road 
St Leonard, Maryland 20685 
Population dynamics of blue crabs 
( Callinectes sapidus) can be studied 
by using a variety of fishery depen- 
dent and independent methods, such 
as the use of crab pots (Abbe and 
Stagg, 1996), bottom trawl data, and 
commercial fisheries landing statistics 
(Lipcius and Van Engel, 1990). Com- 
mercial fisheries data sets provide 
extensive information on blue crab 
landings which are related to popula- 
tion dynamics (Lipcius and Van Engel, 
1990), but pots and trawl information 
are also used because of the need for 
independent assessments of popula- 
tion dynamics. Pots are viewed as an 
important method for assessing blue 
crab abundance through estimates 
of catch per unit of effort (CPUE) 
(Abbe and Stagg, 1996) because CPUE 
is generally assumed to be propor- 
tional to total abundance (Harley et 
ah, 2001). However, previous stud- 
ies have indicated that CPUE may 
not accurately correlate with changes 
in abundance (Harley et al., 2001). 
Factors that have been shown to bias 
CPUE for crustaceans include soak- 
time (Miller, 1974; Smith and Jamie- 
son, 1989a), freshness of bait (Smith 
and Jamieson, 1989b), temperature 
(Sharov et al., 2003), and pot design 
(Miller, 1974; Smith and Jamieson, 
1989b). The usefulness of surveys 
for population assessment depends 
on accurate methods to identify and 
control for these biases. 
Behavioral factors, such as intra- 
specific interactions, affect crustacean 
catch rates and can lead to biased 
CPUE estimates. Studies have shown 
that interactions among conspecifics 
negatively affect portunid crabs and 
American lobster ( Homarus america- 
nus) catch rates (Williams and Hill, 
1982; Jury et al., 2001), and Miller 
(1974) showed that catch rates of 
Dungeness crab ( Cancer magister ) de- 
creased with increasing pot density. 
Jury et al. (2001) observed with the 
use of underwater videotape recordings 
that the aggressive behavior of Ameri- 
can lobsters played a vital role in over- 
all American lobster catch rates. What 
is not clear is whether there is a con- 
sistent relationship between aggressive 
species and pot catch rates. 
The blue crab is an economically 
and ecologically important species to 
Chesapeake Bay (Van Engel, 1958) 
and has well documented intraspecific 
(Jachowski, 1974; Clark et al., 2000) 
and interspecific (deRivera et al., 
2005) agonistic behavior. It is possible 
that blue crab behavior in and around 
crab pots may have a significant role 
on pot catch rate. To address this 
notion, we developed techniques to 
observe crab behavior in and around 
a crab pot. 
Since the 1950s underwater video 
monitoring has been used in marine 
science to observe the behavior of 
fish and invertebrates (Barnes, 1963; 
