Project Overview
Purpose
To better manage marine resources, we need to understand the biology of fishes and what factors impact their behavior. The acoustic tagging project will help managers understand how much time red snapper and three grouper species (gag, red and scamp) spend in particular areas of Gray's Reef National Marine Sanctuary. Also, this project will allow us to track their daily, seasonal, and annual movements to better understand the behavior of these fish. The movement patterns may vary between individual species being studied or between individual age groups.
There are several questions we hope to answer, such as:
- Do resident times differ between species?
- How does temperature or weather affect the amount of time the fish spends in the sanctuary?
- Does the time of day or period in the lunar cycle have an effect on the amount of time the fish spends in the sanctuary?
Acoustic tracking offers many benefits as compared to direct observation or conventional tag and recapture. Direct observations of subjects may alter fish behavior. In contrast, acoustic tagging allows us to detect whether a fish is present in or absent from the target area, without having to be there. Also, conventional tag and recapture can have more impact on the fish since this process requires the fish to be handled multiple times. Acoustic tagging allows us to receive more present-absent data with relatively less stress to a fish.
Fourteen acoustic receiver array units are placed around Gray's Reef National Marine Sanctuary to listen for tagged fish. If you happen to accidentally pull up one of the receiver arrays (Figure 4) please keep the array and call us at 912-598-2345. We will retrieve the unit and return it to the water in the appropriate location so that we can continue tracking fish in Gray's Reef National Marine Sanctuary.
Tags and Receivers
Sixteen fish are currently tagged with transmitters: seven scamp, Mycteroperca phenax, five gag, Mycteroperca microlepis, three, red snapper Lutjanus campechanus, and one red grouper, Epinepelus morio. These fish were caught using hook and line and vented using an empty hypodermic needle. The tags were then surgically implanted into the fish’s abdominal cavity. These tags emit a unique "ping" every 120 seconds at a frequency, which the acoustic receivers can detect up to about 200 meters.
Fourteen acoustic receivers are deployed in the sanctuary. An acoustic receiver array consists of the receiver attached to a buoy line that is suspended vertically in the water column using two subsurface floats and a steel bar as an anchor. The receiver is attached about 1.5 meters from the bottom so that when the bottom gets stirred up by fish or weather the receiver is not affected. Divers retrieve the receivers once every three months, download the data, and then return to the mooring. For more information on the tagging procedure see frequently asked questions or contact us at (912) 598-2345.
Area
Gray's Reef consists of four habitat types: flat sand, rippled sand, sparsely colonized live bottom and densely colonizedlive bottom (site characterization). Receiver arrays were positioned on flat or rippled sand, adjacent to areas of densely colonized live bottom. Snapper and grouper species are commonly associated with densely colonized live bottom. Researchers believe that placing receivers near these areas will increase the chance of fish being detected by the receivers.