Development and evaluation of portable PIT tag detection units: PITpacks

Portable passive integrated transponder (PIT) technology has been used by biologists to study fish behavior non-invasively. However, the method's efficacy has not been evaluated rigorously. To address this, we evaluated the design and field application of three portable backpack PIT tag units (PITpacks) over three years in Abernathy Creek, Longview, WA. Specifically, we assessed options for PITpack design and construction, PIT tag loss and mortality in steelhead trout following the implantation of 23 mm PIT tags, field efficiency of PITpack surveys and the effect of approaching PITpacks on steelhead trout behavior. Our results indicate that antennas constructed of 14 gauge ribbon cable operated consistently when held at a 45° angle to the water surface. Design modifications reduced equipment weight and made PITpacks easier to use. Read range of optimized PITpacks approached 90 cm off the antenna plane when the antenna and tag were submerged in water. Mortality was higher in 23 mm PIT tagged (1.8%) than in non-PIT tagged (0.5%) fish maintained in the same raceways. Tag loss was estimated to be 7.2%, peaked 4 weeks after implantation, and continued at a lesser rate throughout the 4-month study. Instream use of PITpacks resulted in a consistent survey efficiency of 38% in three separate trials. In addition, behavioral observations of tagged fish revealed minimal disturbance to fish approached by PITpacks. Results show that PITpacks can be applied in small streams to study individual fish behavior with only one collection and handling event (for tagging) and minor further disruption.