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;<t?o~ CDlf\-V\o111 ~T Q\ North American Journal of Fisheries Management 28:402-417, 200& American Fi~hcries Socit.1y 2008 001: 1O.1577/M07-008.1 [Article] Measuring the Performance of Two Stationary Interrogation Systems for Detecting Downstream and Upstream Movement of PIT- Tagged Salmonids PATRICK J. CONNOLLY,* IAN G. JEZOREK, AND KYLE D. MARTENS U.S. Geological Sun'ey. Western Fishe/ies Research Center. Columbia River Research Laboratory, 550lA Cook-UndelWood Road. Cook. Washington 98605. USA EARL F. PRENTICE National Marine Fisheries Service, Maru:hester Research Field Station. Manchester, Washington 98353, USA Abstract.-We tested the peIfonnance of two stationary interrogation ~)'stems designed for detecting the movement of fish with pa~sive integrated transponder (PIT) tags. These systems allowed us to determine the direction of fish movement with high detection efficiency and high precision in a dynamic stream environment. We describe an indirect method for deriving an e~timate for detection efficiency and the associaled variance that does not rely on a known number of fish passing the system. By using six antennas arranged in a longitudinal series of three arrays. we attained detection efficiencies for downstream- and upstream-moving fish exceeding 96% during high-flow periods and approached 100% during low-flow periods for the two interrogation systems we tested. Because these systems did not rely on structurdl components, such as bridges or culverts, they were readily adaptable to remote, natural stream sites. Because of built-in redundancy. these systems were able to peIfonn even with a loss of one or more antennas owing to dislodgement or electrical failure. However, the reduction in redundancy resulted in decreased efficiency and precision and the potential loss of ability to determine the direction of fish movement. What we learned about these systems should be applicab]e to a wide variety of other antenna configumtions and to other types of PIT tags and transceivers. In tracking an individual ftsh's growth, survival, habitat use, and response to environmental changes, the use of passive integrated transponder (PIT) tags has large potential and appeal (Prentice et a1. 1986, 1990; Peterson et al. 1994; Juanes et al. 20(0). These tags do not rely on a battery for power and can uniquely identify individual ftsh throughout their life span, which can be 10 years or more for some species. Because of these and other attributes, PIT tags have become a primary tool for monitoring. juvenile salmonid migration timing and for estimating survival past hydroelectric dams in the Columbia River system (Achord et aI. 1996; SkaIsk1 et aI. 1998; Muir et al. 2001a, 2001b; Zabel and Achord 2004). Similarly, much new information on fish movement, timing, and behavior has been gained by placing PIT tag interrogation systems in streams to detect passing fish (Armstrong et al. 1996; Zydlewski et al. 2001, 2006; Riley et al. 2003). The use of these systems in experimentally controlled settings has provided re- searchers with a new tool for understanding fish behavior (Nunnal1ee et al. 1998; Armstrong et al. * Corresponding author: pconnolly@usgs.gov Received January 11, 21X)7; accepted October I I, 2007 Published online March 13, 2008 1999; Greenberg and Giller 2000; Riley et a1. 2(02). A stationary system in free-flowing streams has promise to detect passing ftsh for continuous periods of time and during times too diffIcult to sample by conven- tional means, such as during high flows and ice cover (Greenberg and Giller 2000; Roussel et a1. 2004). If information on population estimates, survival. or the proportion of fish exhibiting a certain behavior is desired, the efficiency and variability of detecting tagged ftsh need to be detennined (Honan et al. 2007). Following Zydlewski et al. (2006), we did not distinguish between the terms "effIciency" and "prob- ability," and we adopted the term "effIciency" to describe ovemll perl'ormance of a system for detecting passing fish with PIT tags. What we define as "detection efficiency" is the percentage of PIT-tagged ftsh that were detected when and if they pa~sed an interrogation system. Estimation of detection efficiency so defined does not rely on knowing the number of ftsh that were tagged in the population. Zydlewski et a1. (2006) described the major components ("path effi- ciency" and "antenna efficiency") influencing the detectability of a PIT-tagged ftsh that pa~ses an array with one or multiple antennas. What we refer to as "detection efficiency" is the combination of these major components. Relatively few investigations have 402 07/0