Performance of a Full-Duplex Passive Integrated Transponder (PIT) Antenna System in Estuarine Channels

Passive integrated transponder (PIT) technology is rarely utilized in estuaries due to (1) saline water’s attenuation of an antenna’s electromagnetic field, (2) rapidly changing water properties and levels, and (3) the challenges of installing and maintaining antennas in silty, brackish conditions. We present methods for the construction and installation of antennas that can detect 12-mm full-duplex PIT tags in salinities up to 33‰. We evaluated their reading performance under variable water salinities, temperatures, and depths in the upper estuaries of three streams. We found that water depth, salinity, and temperature were all negatively correlated with antenna current, but that the relative importance of these variables varied depending upon aspects of the antenna deployment. Since our antennas held amperage levels adequate for maintenance of a complete electromagnetic field throughout all test conditions, we suggest that successful detection was more dependent upon the antenna system’s coverage of the water column and the swimming path of fish through the antenna system than individual antenna performance. In addition to fish, this technology could be applied to studies of mammals, crustaceans, and particles transported through estuarine channels. Recently, researchers have emphasized the need to better understand fine-scale estuarine habitat use by fish, particularly salmonids (Bottom et al. 2005; Koski 2009; Roegner et al. 2010). Estuaries provide critical habitats for multiple stages of salmonid life cycles by allowing rapid growth, acclimation to salinity, and the expression of multiple life histories, factors that may increase survival and population resilience (Reimers 1971; Tschaplinski 1982; Virtanen et al. 1991; Thorpe 1994). Because the deployment and use of some fish-tracking technoloSubject editor: Donald Noakes, Thompson Rivers University, British Columbia, Canada *Corresponding author: [email protected] Received July 28, 2011; accepted February 19, 2012 gies is complicated or hampered in environments characterized by fluctuating water chemistry (including high salinity) and levels, much less is known about salmonid behavior and habitat use in estuarine marsh channels than in freshwater streams. Radiotelemetry, an important tool in the study of fish migrations, has had limited applicability in monitoring juvenile fish movements in brackish estuaries due to the attenuation of electromagnetic frequencies in saltwater. Acoustic tags work well in estuaries, and a smaller tag has recently been introduced that 145 D ow nl oa de d by [ O re go n St at e U ni ve rs ity ] at 1 1: 07 2 6 N ov em be r 20 12