Sturdivant and Clark: Effects of Callinectes sapidus behavior on the efficacy of crab pots for estimating population abundance 
49 
Myrberg, 1973). Early underwater video recording tech- 
niques, which are still in use, include towed video sleds 
(Chapman, 1979), hand-held video cameras (Potts et ah, 
1987), and remotely operated vehicles (ROVs) (Spanier 
et al., 1994). Although in situ video recording is ideal, 
high turbidity (as in Chesapeake Bay) can prevent the 
use of this technique. In the absence of in situ video 
surveillance, mesocosm studies are very effective be- 
cause the environment can be manipulated to allow for 
accurate observation in representative constructions of 
the natural setting. 
By combining in situ experimentation with mesocosm 
observation, we attempted to assess whether blue crab 
behavior affected crab pot efficacy. The specific objec- 
tives of this study were 1) to determine whether intra- 
specific interactions affect catch and escape rates with 
respect to crab size and abundance; 2) to determine if 
catch or escape rates are influenced by abiotic factors 
such as depth or the submersion time of pots; and 3) 
to assess the effects of blue crab behavior on crab pot 
efficacy. 
Materials and methods 
Study site 
The study took place during July and August of 2003 
at the Smithsonian Environmental Research Center 
(SERC), in Edgewater, Maryland. Field experiments 
were conducted at Canning House Bay (CHB), a half- 
moon-shaped embayment of Chesapeake Bay in the 
Rhode River. CHB is characterized by sandy beaches 
intermingled with coarse woody debris, marsh plants, 
and ever-encroaching populations of common reed 
( Phragmites spp.). The Rhode River is a subestuary 
that connects to the mesohaline central Chesapeake Bay. 
Water temperatures in the Rhode River peaks in July, 
with an average of 27-28°C, and summer temperatures 
can exceed 30°C along the shore. Salinity varies season- 
ally in the river from 3 to 17 ppt. Mean tidal amplitude 
in the river is 0.3 m, and mean low tide level is 0.2 m 
above mean lower low water. Daily tidal action in the 
Rhode River is highly influenced by winds, and tidal 
fluxes greater than predicted can occur. Turbidity in 
the Rhode River is often high in summer, with Secchi 
depths <0.5 m (Everett and Ruiz, 1993). 
Crab pots 
We employed commercial crab pots used by waterman in 
Chesapeake Bay (Van Engel, 1962) to test crab-pot catch 
rates. The pots are square wire-mesh (3.8 cm) cubes 
55.9x61.0x55.9 cm, with an upper and lower section. 
The lower section is called the kitchen or bait chamber, 
and the upper section is called the parlor or trap cham- 
ber. There is an entrance on each of the four sides of the 
kitchen, and a conical bait well is situated in the center. 
The kitchen and parlor are separated by a wire-mesh 
panel, raised in the middle to form an inverted V. There 
are two openings along the apex of the V that lead into 
the parlor. The parlor contains two circular escape holes 
(cull rings) on either side to provide an exit for sublegal- 
size crabs (smaller than 127 mm). Pots were attached to 
floats with a 2.5-m line for retrieval. 
Field experiment 
Field experiments were conducted to assess the effects 
of blue crab size and water depth on catch and escape 
rates. Before the pots were set, test crabs were placed 
to seed (placing crabs in pots before experimental run) 
the pots in an attempt to initiate behavioral interactions 
amongst crabs to determine if the presence and size of 
a crab in a pot affected catch rates. Three water depths 
were examined: shallow (1 m); medium (2 m); and deep 
(3 m); the maximum depth of the study site was 5 m. 
These depths were chosen on basis of previous work at 
this site by Ruiz et al. (1993) who showed a difference 
in the abundance and size of crabs with depth. The pots 
were placed on a muddy substrate free of vegetation or 
other structured habitat. Test crab sizes were classified 
as large, small, and control. Large crabs were defined as 
greater than 155 mm carapace width (CW), small crabs 
were 127-130 mm CW, and a control of no crabs was also 
used. The crab size of 127 mm CW was the minimum 
size for legal catches in Maryland during 2003, and 
is the minimum size of crabs that cannot fit through 
the escape ring on the pot. This limit was set because 
of our interest in blue crabs that are considered legal 
catch. There were three sampling areas within Canning 
House Bay, and three pots were placed in each area. 
Areas were evenly spaced within CHB, and each area 
contained a deep, medium, and shallow water depth (1-, 
2-, and 3-m depths). The pots and depths were distrib- 
uted in a full 3x3 factorial design. Test crabs used for 
this experiment were collected predominantly by trawl- 
ing, and occasionally in pot catches, both of which were 
undertaken separately from the experiment. To reduce 
behavioral variance, test crabs had all appendages and 
were males in molt stage C, an intermolt stage when 
crabs are presumed to exhibit standard behavior. 
During an experimental run, a single test crab was 
measured, numbered, and placed in the kitchen of each 
pot before initial deployment. Test crabs were held in 
deck tanks until needed, and were fed chopped pieces 
of partially frozen alewife ( Alosa pseudoharengus ) un- 
til 24 hours before being placed in the experiment. 
Pots deployed in the field experiment were also baited 
with chopped pieces of partially frozen alewife. The 
bait was chopped, frozen, and then placed in the bait 
wells of pots before deployment. Catch rates of pots 
can vary with fresh and frozen bait; however, owing 
to logistics, frozen bait was used for this experiment. 
However, because of the summer heat, the bait became 
partially unfrozen by the time the sampling area was 
reached and pots were deployed. Pots were placed at 
depths of 1, 2, and 3 meters in each area of CHB for 48 
hours. A single experimental run was 48 h, divided into 
two 24-h periods. After the first 24 hours, pots were 
