Passive integrated transponder (PIT) tags are a commonly used technique for identifying and tracking organisms as they are small, cost-effective, and can operate indefinitely. These tiny tags take advantage of the same technologies as the “chips” used to identify pets, the push-button ignition systems that recognize when your car keys are present, and the touchless locks used on buildings around the world. Since the chip is powered by the magnetic field emitted from the reader, it can remain active until it breaks down materially (a very, very long time in the case of these glass-encapsulated tags).
There are two main detection techniques used in fisheries PIT tag research. Permanent, stream-width detection arrays are very common and capable of identifying nearly all tagged organisms passing a particular point on a linear stream system but require significant infrastructure to install and maintain. The alternative, portable backpack detection units, are more suited to small streams and short-term work, but rely on labor-intensive manual surveys for tagged organisms that may be disruptive to fish behavior.
To complement these methods, we’ve developed a technique using multiple, independent, small-scale PIT readers. An array of these readers is cost-effective and can collect data autonomously. The use of small pass-over antennas also allows for placement in nonlinear waterbodies, such as lakes and ponds, where travel direction cannot be assumed and pass-through antennas are therefore of limited utility. This system does not replace current methods but instead expands the utility of these widely used tags and creates new research opportunities.
We’re currently using this technique to assess the recovery of brook trout and lake trout in multiple Adirondack lakes.