Dataset: Blue crab acoustics

Location: 
Gulf coast of Florida outside of Tampa Bay (27 N & 82 W); < 7m depth
Eastern shore of Virginia; Atlantic coast; (37 N & 75 W); < 7m depth
Atlantic coast of Florida outside mouth of St. Johns River; (30 N & 81 W); < 7m depth

Sampling and analytical procedures:
At each site, commercial style blue crab traps were baited and deployed in the area where we wished to study crab movement. After 48 hours, traps were checked and if at least 10 crabs were found in the traps we deployed an array of 17 Vemco VR-2Tx hydroacoustic receivers attached to PVC poles set into concrete bases. The GPS location of each receiver was recorded and each was approximately 100 meters from any other receiver. We then placed Vemco V9 hydroacoustic tags on the backs of 9 to 11 crabs using aluminum wire and released them at the center point of the receiver array. The size and sex of each crab was recorded prior to release. After 48 to 72 hours, the receivers were retrieved and the raw hydroacoustic data were downloaded and analyzed.

The potential pathways of tagged crabs were estimated using a Center of Activity analysis following Simpfendorfer et al (2002). Estimates of latitude and longitude were made from the mean center of detections within the receiver array over 15-minute intervals for each transmitter. The mean center at a given time was weighted relative to how many receivers detected a transmitter during an interval (e.g., if a crab transmitter was recorded 3 times, 2 times and 15 times on receivers A, B and C respectively then the mean would be the average position of 3 × receiver A + 2× receiver B + 15 × receiver C). Bearings and velocities were calculated from the position estimate at the last interval. If a transmitter was not detected during the previous analysis interval, a position estimate would be recorded, but no bearing or velocity would be recorded, and the crab was considered inactive. This ensured that velocities and bearings were only recorded during times at which a crab was actively moving to best couple the appropriate environmental data. If a crab was absent for many sequential intervals while within the array, it was assumed to have buried or otherwise masked its transmitter. Analysis was conducted between the first and last position estimate for each crab within the array to encompass only the timespan when the crab was known to be detected by the array.

Tidal impact was examined using tide and current data from NOAA stations nearest the site locations.  Values were obtained from the NOAA Tide and Current Dataserver:

• Virginia site location used  the Wachapreague, VA station (# 8631044)
• Jacksonville site location used the _________ station (# 8719525 (??)
• StPeteMay site location used the Clearwater Beach, FL station (# 8726724)

The values are height from MLLW (mean lower low water--relative to the water level at the lowest daily low tide). We looked at the difference from the last predicted instance to see if the tide was actively increasing or decreasing and the relative strength of that increase.