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Tagging Salmon Smolts Using Acoustic Telemetry

Video demonstrating how salmon smolts are tagged using acoustic telemetry. Credit: NOAA Fisheries/Heather Soulen

Transcript of Video Voice-over:

Acoustic telemetry is a tool that scientists around the world use to identify behaviors and track the migration of tagged animals found in rivers, lakes, and oceans. We're using it to understand more about Atlantic salmon smolt movement as they travel from the upper reaches of the Narraguagus River in Maine, through the estuary, and into the ocean. Prior to this journey, we must surgically insert these acoustic transmitters -- which are approximately the size of Jolly Rancher -- into the abdominal cavities of these salmon smolts.

Surgeries are performed either streamside, or as in the case of this study, a hatchery. To get started, we must first net the smolt and then place it in anesthetic. In this case, it’s Tricane Methanesulfinate, or MS-222, to sedate and allow us to easily handle the fish for sampling and surgery.

We first observe and note the condition -- or apparent health -- of the smolt, and take measures of length in millimeters and weight in grams with the only criteria that the smolt is greater than 150 millimeters or approximately 6 inches in length. This is a large enough size to insure that the transmitter won’t impact movement and survival of the smolt in the wild.

Prior to the surgery, a physiology sample is collected by using scissors to remove three to five gill filaments from the smolt. This allows us to measure the physiological condition of each smolt, or their ability to transition from fresh to saltwater.

Now we begin the surgery procedure. Using a sterile scalpel, we make an incision on the abdomen between the pectoral and ventral fins. This incision is three quarters of the length of the transmitter, or approximately half an inch, which will allow plenty of room to insert the transmitter. The transmitter is inserted into the smolt by carefully placing one end into abdominal cavity and pushing it in slowly, at an angle, towards the tail. Once the transmitter is in the smolt, we use a suture to close the incision using two simple interrupted knots. Once the knots are complete, we put antibiotic ointment on the incision to promote healing and prevent infection. The surgery takes less than 2 minutes and the smolt is fully recovered within 5 to 10 minutes.

Each acoustic transmitter surgically implanted into these salmon smolts emits a unique coded number which allows us to identify individual fish. As the smolt travels downstream an acoustic signal is emitted every 20 to 40 seconds. These transmitters are detected by receivers that are strategically placed throughout the river, estuary, and ocean to provide high resolution coverage which will allow us to answer questions on behavior and other migration parameters that we are interested in.