A 12 mm PIT tag that’s inserted into fish for tracking purposes isn’t much bigger than a grain of rice.

A 12 mm PIT tag that’s inserted into fish for tracking purposes isn’t much bigger than a grain of rice.

The movement and distribution of fish in bodies of water in Idaho are monitored with passive integrated transponder tags.

Commonly known as a PIT tag, the tiny devices are similar to a microchip and about the size of a grain of rice, according to Idaho Fish and Game fisheries biologist Stacey Meyer.

Tags are inserted into fish using a sterile needle with an injector. Each PIT tag has a unique tag code that allows for individual fish identification. After the tag is inserted, data such as species, length and weight is recorded, and the fish is released and tracked by its unique code.

Tracking fish with PIT tags and PIT arrays is different from tracking big game animals with radio collars, Meyer said. Radio-collared animals can be tracked at most locations using satellites or handheld receivers. PIT tags do not have a power source, and require activation from an instream antenna, known as arrays. PIT-tagged fish must pass within a few feet of an array to be activated and detected. Once the fish is detected, the PIT-tag code, date and time is uploaded into the Columbia Basin PIT Tag Information System. That creates a history of locations and times a particular fish is detected.

PIT array locations are selected so fish distribution and movement can be monitored for management reasons.

The Lemhi River has four arrays in the main stem and more arrays at the mouths of tributaries. In the Lemhi River basin, PIT arrays are commonly used to better understand where juvenile fish overwinter and how habitat in those specific locations is related to overwinter survival.

PIT-tag arrays are located throughout the Pacific Northwest so biologists can track Chinook salmon and steelhead between freshwater and saltwater and through multiple states. Arrays can be used to observe fish passage at dams, as well as monitoring fish screens that are designed to bypass fish around irrigation diversions.

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