Accelerometry of Juvenile Lemon Shark Feeding Events
University of North Carolina Wilmingtion
Ultrasonic telemetry has been used to study various aspects of shark biology, including movements, swimming speed, heart rate, and stomach pH and temperature, but has not been applied to the movements that sharks make while foraging. A new ultrasonic accelerometer transmitter will be used to telemeter foraging behavior of juvenile lemon sharks, specifically by telemetering a shark's lunge at a prey item. The objectives of this study are to investigate the utility of ultrasonic accelerometry for studying shark foraging, gain direct evidence of juvenile lemon shark foraging in the wild, determine foraging locations within the nursery, and examine diel patterns of foraging.
Conducting transmitter trials
in the pen
The accelerometer transmitter emits a coded pulse to allow trackers to recognize and follow the shark, and additionally emits a fast alarm pulse whenever it detects a change in acceleration greater than or equal to 1.5 g (1g = 9.8 m/s2). Transmitters will be attached externally, at the base of the first dorsal fin.
To get quantitative information about the accelerations juvenile lemon sharks make, captive trials will be conducted. During these prototype testing trials, the total number and time of acceleration events will be recorded. Visual observations as well as stomach content analysis will be used to determine whether accelerations were associated with successful versus unsuccessful feeding events or other non-foraging behaviors. In addition to both pre- and post-consumptive observations, individual sharks will undergo trials with a small school of 12 yellowfin mojarra (Gerres cinereus) between 5 and 25% of the shark's total body length. It is unlikely that prey will be consumed without hearing an acceleration alarm, therefore the following hypothesis will be tested: the number of prey pursued, attacked and consumed by each shark will be positively correlated with the number of acceleration events.
Sharks will also be tracked in the wild to determine locations of accelerations and locations of foraging. At the end of a track, the shark will be captured and stomach contents will be collected using a non-lethal stomach eversion procedure. Stomach contents will be identified and digestion state will be assessed to determine if the prey item was consumed at the time of the acceleration.
Tracks will be mapped in a Geographic Information System in order to track the physical locations of foraging events and classify them based on distance from the mangrove fringe. The following hypotheses will be tested: 1) habitat will have no effect on feeding behavior, 2) feeding events will occur during all times of day, 3) habitat will have no effect on the diet, 4) time of feeding events will not affect the diet, and 5) the number of prey items in a shark's stomach will be positively correlated with the number of accelerations.
Bimini's nurseries are critical for lemon sharks because the shallow, mangrove-lined lagoon provides them with a source of food and some protection from predators. Because the juvenile lemon shark is the top predator on teleost fishes within this ecosystem, understanding its feeding ecology is crucial for understanding the system as a whole. This study will provide the first direct evidence of wild juvenile lemon shark foraging as well as introduce new technology applicable for foraging studies of predators. It will also be the first study to examine the importance of physical location within the nursery on juvenile lemon shark foraging.
< Back to Research List