Tracking Shark Movement in Rhode Island
If you spend any time on the beautiful RI waters that many of us call home, there is a good chance that you may have seen, or unknowingly cruised over, an acoustic receiver. Rhode Island’s network of acoustic receivers is important for understanding the movement of many marine species, including sharks.
While some states along the East Coast had extensive acoustic telemetry arrays, prior to 2019 there were no acoustic receivers deployed in the State of RI. This led to some marine scientists to refer to RI as an acoustic telemetry “black hole”. However, all that changed in May of 2019 when the Atlantic Shark Institute (ASI) and the RI Department of Environmental Management (RI DEM) collaborated on deploying 12 acoustic receivers for the very first time in RI waters. And that was only the beginning, as for the 2024 season, more than 45 acoustic receivers will be deployed!
An acoustic receiver is a waterproof device that detects acoustic pings from acoustic transmitters (tags) underwater. These tags are attached to all types of species worldwide. The tags come in all shapes and sizes, so they can be attached to large animals like sharks and whales, and even smaller fish such as herring. The receiver itself is about the size of a medium Thermos. They last an entire research season with one set of fresh batteries and can listen for tags continuously. For our array, we usually have the receivers deployed for 7-8 months of the year. The biggest issue that we run into is the potential loss of equipment due to weather. If we lose the receiver, we lose all the data, and that is something we work very hard to avoid. As a result, during the deployment season we will go out periodically to pull all the data off the receivers via Bluetooth.
The tags each have a unique code that acts like a social security number. When an animal with an acoustic tag swims within a certain distance of an acoustic receiver (within several hundred yards), the receiver picks up that transmission, captures it, and adds a date and time stamp. Researchers can then see exactly when and where their tagged animal was observed, and for how long.
The ocean is always changing. What we knew 10 years ago about a species distribution and migratory patterns may or may not stay the same. Quality research, conducted with proven methodologies, is key to informing sound management decisions. New tagging technologies are playing a larger and larger role in that research. 20 years ago, if we caught a great white shark for example, we would put a plastic tag on it, release it, and hope someone caught the same shark sometime later to determine where is went. Today, when we catch a great white shark (the ASI has tagged and released more than 30), we have a wide variety of tags to choose from, including acoustic tags. We can place an acoustic tag on the shark and track its movements for up to 10 years! With hundreds of receivers up and down the East Coast, information about shark movement is much more accessible and helps answer important questions about their behavior.
The amazing thing about these receivers is the wide variety of tagged animals that we have detected. While the Atlantic Shark Institute focuses on sharks, both the ASI and DEM receivers pick up any acoustic tagged animal that swims by. Our receivers have detected numerous shark species, including white, mako, blue, sand tiger and many others. We’ve also detected tuna species, sea turtles, sturgeon, striped bass, winter flounder, and black sea bass.
One example of acoustic data for a tagged fish is displayed in the map above. This map shows the movement of a thresher shark tagged by RIDEM and ASI spanning over two years. This shark was tagged near Rhode Island in June 2021 and was most recently detected in July 2022. This coastwide network of acoustic receivers allows us to understand how far sharks travel and where, as well as the timing of their movements.
To learn more about the ASI, please visit our website at www.atlanticsharkinstitute.org.
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The movement of a thresher shark tagged in Rhode Island in 2021 and detected again in 2022.
An acoustic receiver listening for pings at the Block Island Wind Farm.
An acoustic tag ready for deployment.
