Ultrasonic Biotelemetry of Muscle Activity from Free-Ranging Marine Animals: A New Method for Studying Foraging by Blue Crabs (Callinectes sapidus)

Abstract

Abstract. The design and utilization of a small (16 g in air, 6 g in water) ultrasonic transmitter for animal tracking and bio-telemetry of muscle activity are described. To our knowledge this is the first use of such devices to telemeter a specific behavior (ingestion) from a free-ranging marine predator. The transmitter produces regularly recurring short tracking pulses, and long pulses triggered by the action potentials of a muscle. Pulses are transmitted through conductive estuarine water by a piezoelectric ring transducer at a frequency of about 75 KHz. The preparation of a subject animal, insertion of electrodes, and attachment of the transmitter are described for the telemetry of mandibular muscle contraction in the blue crab. The transmitter provides a signal that corresponds unequivocally with feeding activity and allows enumeration of bites required to consume a food item. Number of bites, and feeding time, are both positively correlated with the size of the prey specimen. As a test of the technique's feasibility, a blue crab was equipped with one of the transmitters and released in a subestuary of Chesapeake Bay. The crab was tracked continuously for 96 hours while every contraction of the mandibular muscle was recorded. The crab traveled 4000 m along the subestuary at an average speed of 12 m/h, but showed periods of rapid movement of up to 325 m/h. The crab fed 2-7 times per day, with a feeding bout comprising 15-2750 bites. The limited data did not indicate that either movement or feeding exhibit a diel or tidal cycle. Introduction We describe the design of a new ultrasonic telemetry transmitter for relatively small marine or estuarine ani-

Foraging and agonistic activity co-occur in free-ranging blue crabs (Callinectes sapidus): observation of animals by ultrasonic telemetry

“…Crabs moved in patterns similar to those observed in previous field tracking experiments, 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. The data pooled over all five crabs yielded a mean velocity of 11.94 m / h (SE 5 2.02), similar to the 12 m / h reported by Wolcott and Hines (1989). Mean velocity of individual crabs ranged from 0.77 to 36.23 m / h (Table 1).…”

“…To verify that movements of crabs were qualitatively consistent with those from previous field tracking experiments (Nye, 1989;Wolcott andHines, 1989, Wolcott and, we mapped each crab's track onto a chart of the river. Quantitative comparisons were made by calculating velocity of movement (mean, SE, and range) for each crab and for the pooled data from all five crabs.…”

“…Feeding was telemetered by sensing biopotentials of the crab's mandibular (chewing) muscle (Wolcott and Hines, 1989). Electrode sites were cleaned with acetone, drilled nearly through the calcified exoskeleton, and covered with a rubber membrane (dental ® dam) affixed with cyanoacrylate glue (Hysol 2-C-500).…”

“…Blue crabs appear to aggregate at high densities while foraging; they feed primarily on patchy resources (clams) and appear able to detect these patches from at least 10 to 15 meters (Clark, 1997;Hines, Terwin, and Thrush, unpublished data). Once on a patch, they generally remain there long enough to consume multiple prey (Nye, 1989;Wolcott and Hines, 1989). Both laboratory studies and indirect field evidence indicate a high level of intraspecific agonism as crab density increases (Smith, 1990;Mansour and Lipcius, 1991;Smith and Hines, 1991).…”

Behavioral responses of free-ranging blue crabs to episodic hypoxia. I. Movement

“…We used a multichannel biotelemetry system to monitor movement of individual free-ranging blue crabs. The biotelemetry system was adapted from previous designs used to observe behavior of free-ranging blue crabs (Wolcott & Hines 1989, Clark et al 1999a,b, 2000. The electronic circuitry of the transmitter was packaged in shrink tubing which was molded to conform to the dorsal surface of the carapace (to reduce drag), and filled with mineral oil to couple sound between the transducer and water.…”