While the tag-and-recapture program has provided some unique and new information on bonefish movements and population dynamics, the process only provides the particulars on the “start” (i.e., tagging) and “end” (i.e., recapture) of the journey. There is no information on the in-between period to define locations during the migration, habitat use, site fidelity, or relationship to movements and environmental conditions. To address this issue and to compliment the data obtained by conventional tagging procedures, we are currently conducting an acoustic telemetry (AT) experiment to track and monitor bonefish ( Albula vulpes ) to study their high-resolution movements in space and time, site fidelity, habitat use and spawning migrations in the northern Florida Keys. Acoustic telemetry is a method that allows for continuous tracking of fish movements in a cutting-edge process that uses underwater technology similar to that employed by the US Navy's sub-detection program.

In the AT process, bonefish are fitted with a coded transmitter tag.
The surgically implanted transmitter “tags” are about 1.5 inches long and 0.5” in diameter that are surgically implanted into the bonefish in the field (far right) or tagged at the University of Miami hatchery and released at a later date. The transmitters use a digital method to emit acoustic pulses on a specified frequency, allowing unique identification of each tag (i.e., individual bonefish) by the receivers.

These tagged "acoustically-active" bonefish are then released into a networked array of a strategically placed array of hydrophones (listening devices) that are alerted to the fish's presence when the acoustic signal reaches a given receiver. We are using VR2 submersible, single channel receivers from VEMCO capable of identifying coded transmitter tags.

The VR2 consists of a hydrophone, ID detector, data logging memory, and battery all housed in submersible cases and fitted with an anchor weight (below far left), and then moored at specific locations (below far right ). Each VR2 has a battery life of at least 6 months post-deployment and batteries are easily changed in the field. When a “tagged” bonefish travels within receiver range (~250 meters), the implanted acoustic transmitter will send out a series of pings. The transmission time lasts about three seconds and includes the ID code of the transmitter. The VR2 then records the tag's unique identification number and time stamp. The transmission is followed by a period of silence (typically 20 to 45 seconds) before it repeats. The long silent interval means there is ample opportunity for other transmitters (i.e., tagged bonefish) to be detected. Data from the receivers is periodically downloaded in the field using a magnetic probe and PC interface. Several thousand fish can be tracked simultaneously with the system. In this study we plan to “tag” about 50 to 100 or more bonefish. We'd love to have you join us at RSMAS and in the field to see and experience our operation working to learn more about bonefish and to conserve this precious fishery resource.

Use of this remarkable technology has allowed us to provide nearly continuous tracking of bonefish movements over relatively large areas (Humston 2001, Ault et al. 2002a, Humston et al. 2005). In the first phase of our acoustic telemetry research w e used an acoustic telemetry system used to test the hypothesis that bonefish exhibit site fidelity in selection of foraging areas in the northern Florida Keys (Humston et al. 2005) . Stationary hydrophone receivers with data logging units were deployed surrounding a discrete bonefish foraging area. Individuals were captured, fitted with acoustic transmitters, and then released within the study area. The reception ranges of receiver stations within the array were evaluated by moving a transmitter within the array. These data were used to assess spatial coverage of monitoring and decipher fine-scale movement patterns from recorded presence-absence data. Sixty-four percent of tagged fish were detected by receivers for multiple days following release. Tagged fish frequented the experimental area for periods ranging from 3 to 61 days. Only two individuals, tracked for 48 and 61 days, demonstrated site fidelity characterized by daily movements into the study area.

Our observations contradict earlier studies that concluded bonefish ranged widely throughout available habitats and suggest that bonefish utilize shallow habitats most, though deep channels may provide refuge from the rapid temperature changes that occur on the shallow flats. At the present time, we are involved with a more extensive study to focus more broadly on aspects of bonefish movements that include site fidelity, home range, habitat use, and spawning migrations. The knowledge gained from our previous study was used to create a new bonefish tracking study with an increased spatial coverage of the receiver array. To accurately capture the spatial extent and fine-scale aspects of bonefish movements the receivers were deployed in an array that covered the long-shore region of the barrier islands and the cross-shore region of the barrier islands to coral reefs in the Atlantic ocean extending from just south of Key Biscayne to south Biscayne Bay (far right ). We also increased the size range and numbers of bonefish tagged than that of the pilot project. This new study allows us to examine the spatial dynamics of bonefish in south Florida by the configuration of the deployed stationary hydrophone receivers that continuously log the date and time of tag detections.

To date, thirty-two bonefish have been tagged with acoustic transmitters and then released in our 40+ receiver array in south Florida . We have logged a total of 51,204 tag transmissions by 36 of the hydrophone receivers (below). Each bonefish has provided records of distinct movement patterns over time and space.

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