How Scientists Track Fish with Acoustics

On land or in the sea, scientists are studying how animals move locally and regionally for migratory, feeding, and spawning purposes. Last summer, I worked extensively with a research professor at Washington College to track the localized movements of eastern painted turtles, Chrysemys picta, in response to rapid environmental change. This week, I am categorizing ground-truthing photographs and editing video from NOAA Ship Nancy Foster cruise 05, which primarily set sail to acoustically track snapper and grouper species movements within the Florida Keys National Marine Sanctuary. I cannot quite say that I’ve tracked both terrestrial and marine species, but I know now that it’s not as other-worldly as one would presume.

The project was accomplished by a cooperative effort between NOAA and the Florida Fish and Wildlife Conservation Commission (FWC), who was the lead organization on the project. During the cruise, diver operations commenced to service forty-two existing acoustic receivers, install over thirty new receivers, and acoustically tag a variety of snappers and groupers, including mutton snapper, black grouper, and scamp. The acoustic receivers are located between Key Largo and Riley’s Hump, a coral reef located within the Tortugas Ecological Reserve South. The receivers record the unique tag ID of a tagged fish when the fish swims within the 309 square mile range of the receiver (“Acoustic Telemetry…”), and the data is collected from the receiver when divers visit the site once again to download what has been recorded.

Fish are collected for tagging by means of a passive fish trap that is sunk to the seafloor, allowed to soak for four hours, and then checked. If target species are in the trap, divers will go to the trap and remove the fish, one at a time, and make a small, inch-long incision between the pelvic and anal fin to insert an acoustic tag. The incision is closed with a few stitches, and the fish is released after a short period of monitoring. The procedure is minimally invasive, and is purposely done in situ, underwater, to minimize animal stress and maximize rate of recovery.

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Left: Scientists stitch the small incision made for the acoustic tag.

Right: A newly tagged Gray Snapper, Lutjanus griseus, is released into the reef. Image credits: FWC.

In addition to collecting data on fish populations and migratory routes, the cruise scientists also set out to collect essential visual data of the habitats immediately surrounding the acoustic receivers. Used in ground-truthing efforts, the photos and videos expand the amount of verifiable benthic habitat of the unified reef habitat map of the sanctuary, which currently has about 75% of the seafloor habitat visually confirmed. This week, I have access to the imagery taken at many of the receiver locations, and am currently processing them to identify the clearest panoramic photos and screenshots that summarize the benthic habitat classification. As soon as the GPS coordinates are processed for the visual data, I will be able to create a points file for the receiver locations in ArcMap and be able to link individual photos or videos to the points for easy interpretation.

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An acoustic receiver in Riley’s Hump.

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A brightly colored panoramic image of the seafloor, along with a goliath grouper, Epinephelus itajara, center.

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A second panoramic image, showcasing the variety of organisms.

All above image credits to the FWC.

References

“Acoustic Telemetry Tracks Florida Keys Reef Fish” MyFWC. MyFWC, 2011. Web. 8 July 2015. http://myfwc.com/research/saltwater/telemetry/projects/tortugas/

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