Acoustic Telemetry -
Fine Scale Fish Movement

Fish observing divers deploy acoustic receiver array. (Photo: Greg McFall, GRNMS)

Gray's Reef National Marine Sanctuary has been conducting an acoustic telemetry project since 2008. The initial purpose of the acoustic tagging project was to determine the broader scale movement patterns of red snapper Lutjanus campechanus, gag grouper Mycteroperca microlepis, and scamp grouper Mycteroperca phenax within the sanctuary. During the NOAA Ship Nancy Foster cruises in 2008, 2009, and 2010, scientists tagged 40 fish (23 gag, 6 red snapper and 11 scamp) and deployed 22 acoustic receivers, which listen for the tagged fish. Red snapper, gag, and scamp have been detected in the array at different times throughout the course of the study. Red snapper show a distinct diel (daily) movement pattern, which means that they are active at night and fairly inactive during the day. Gag and scamp moved more in accordance with the tides at Gray's Reef.

Fish holding tanks on NOAA Ship Nancy Foster. (Photo: Devon Dumont, UGA MECA)

This year, scientists plan to tag 20 more fish (including black sea bass Centropristis striata) and deploy a finer-scale acoustic receiver array to determine fish movement around a single reef site within the Gray's Reef Research Area. Gray's Reef scientists will be collaborating on this effort with scientists from National Marine Fisheries Service in Panama City and the Florida Fish and Wildlife Conservation Commission. Fish will be captured underwater using divers or traps and will undergo surgery on the seafloor. The underwater surgeries will help to minimize the amount of stress experienced by the fish being tagged. The fish will have an internal transmitter tag surgically implanted into their abdominal cavity. Hook and line fishing will be used to capture fish if underwater efforts do not result in 20 tagged fish. Whether underwater or aboard the Gray's Reef R/V Joe Ferguson, fish will be measured and tagged externally with "spaghetti" tags. Fish will be observed until healthy habits (swimming actively and upright) are resumed. The fish will be released at the same site where they were captured. The implanted transmitters will last for roughly three years before the battery dies.

Katalin Zakar (l) and Devon Dumont (r), assist Greg McFall (c) during surgery to implant acoustic recivers. (Photo: Debbie Meeks, GRNMS)

To track these 20 fish, divers will deploy a VEMCO VR2W Positioning System (VPS) (for more information on the telemetry equipment and VPS, please see click here ). This involves placing 6 receivers within 100 meters of each other surrounding the study site, so that a tagged fish can be detected by at least 3 different receivers. This information will tell us exactly where the fish is on the ledge and where it moves throughout its days in the area.

Another objective of the cruise is to service existing receivers deployed in the sanctuary and reposition some of those receivers to new sites. The transmitters within each fish emit a unique signal every two minutes. This signal is detected by any receiver within range of that signal. Servicing receivers involves recovering receivers to download data, replacing batteries and redeploying the receiver. Retrieving the information from the receivers requires that divers recover the receivers from the seafloor, bring them to the surface and connect them to a computer for downloading.

Tagged fish released at capture site. (Photo: Devon Dumont, UGA MECA)

Under a new regulation effective December 4th, 2011, the southern third of NOAA's 22-square-mile Gray's Reef National Marine Sanctuary is now a research area. Fishing and diving are prohibited in the research area, but vessels are allowed to travel across the area as long as they do not stop. Acoustic receivers are located both within and outside of the research area. The tagging project will enable scientists to see whether the fish located outside of the research area exhibit different movement patterns than the fish inside the research area. Data from this project will be crucial in determining if there is an adequate level of resource protection being provided for the fishes that make the habitats of Gray's Reef their home.