Acoustic Detections Reveal FAD Depth Use
August 2023
Since last summer, acoustic transmitters have been deployed at 10 deployment sites among 6 different pelagic fish species. A total of 26 acoustic tags have been deployed in conjunction with the FAD research program and 201 detections have been obtained. Those equate to 104 depth, 93 temperature, and 4 unitless detections. Yellowfin tuna was the species that dove the deepest next to a FAD (up to 150 meters). An unknown predator that ate a tagged dolphinfish dove deeper than the yellowfin tuna but it’s unknown what species the predator was. That predator was detected at FAD D on two separate occasions 11 days apart. Aside from this multi-day detection, a silky shark tagged and released at FAD C with an acoustic tag was detected at that FAD on the same day and next day. These are the only acoustic tags that have been detected at a FAD on different days, and the predator was the only movement from miles away to a FAD with an acoustic hydrophone. Other detection data on dolphinfish has shown that fish tagged with acoustic transmitters at FAD C moved to and from FAD C to the adjacent El Morro Submerged FAD.
Figure left: Counts of acoustic detections among deployment sites (all labeled locations) with red arrows indicating arrows of movement for dolphinfish between acoustic hydrophones. Black ovals are graduated relative to number of detections per station. El Morro Sub = El Morro Submerged FAD. SKJ = skipjack tuna. Deployment of fish at Radares and Hoteles were yellowfin and blackfin tuna.
Figure right: Depth (n=104) and temperature (n=93) fixes gathered from acoustic monitoring dolphinfish, yellowfin tuna, silky sharks, wahoo, and an unknown predator with v16TP acoustic tags among acoustic receivers deployed off San Juan, Puerto Rico.
October 2022- In September, we embarked on a field expedition to re-initiate FAD and acoustic reseach among the FADs deployed off San Juan, Puerto Rico. In this effort, our goals are to better describe fish movements relative to the FADs; fishing trip success and catch and effort; how FAD design can affect species abundance, presence, and biomass; and the impact that FADs have on local businesses and visitors to Puerto Rico. Watch the video above or click here to learn about our recent field expedition off San Juan, PR, in September, where we re-initiated acoustic, camera, and tagging work whereby 4 dolphinfish, 2 yellowfin tuna, and a silky shark were tagged and released with acoustic transmitters. We also redeployed sound hydrophones, temperature instruments, and monitoring cameras. We intend to share updates on data collected from this work in our next newsletter due out in December.
Past Updates – Fish Movements
2019 – Since 2015, we have deployed 12 acoustic V16TP tags on ten dolphinfish, a wahoo, and a blackfin tuna around the FADs. In addition, 547 plastic dart tags have been deployed on dolphinfish (539), wahoo (6), a blackfin tuna (1), and a silky shark. Plus, a total of 12 satellite tags were deployed on dolphinfish (10), a wahoo, and a silky shark. This included 2 high-rate Microwave Telemetry X-Tags and 10 Wildlife Computers mrPAT tags. Below are some figures based on data acquired and collected through June 2019.
