Fine-Scale Acoustic Tracking of Juvenile Salmonids around Engineered Logjams in the Elwha and Hoh Rivers

Studies examining habitat use and behavior by juvenile salmonids in rivers have traditionally been completed using bank observation, snorkeling, or active fish sampling (i.e., electrofishing or seining).  However, these methods generally provide information for a specific point in time and occur for individual fish during a relatively short observation period (i.e., usually minutes).  Fine-scale acoustic tracking on the other hand, allows high resolution observations (± 1 m) of individual fish to be completed continuously for days or weeks, without the potential impacts of snorkeling and/or active sampling methods on behavior.  However, the usefulness of this method has not been fully explored.  The objectives of this study were to evaluate the use of fine-scale acoustic tracking to examine habitat use and behavior of juvenile salmonids at two sites in relatively large western Washington rivers where engineered logjams (ELJs) were recently installed.  Twelve juvenile steelhead were tracked continuously for 0.1 to 7.4 days (ave. 3.7 days) in the Elwha River during the winter of 2005, while 26 juvenile steelhead were tracked continuously for 0.1 to 16.5days (ave. 11.3) during the summer of 2009 in the Hoh River.  Juvenile salmon used substantial portions of the pools during the period they were tracked.  Habitats used by individual fish varied substantially throughout the day as well as between days, suggesting that point observations should be used cautiously.  Examples of using fine-scale acoustic tracking to evaluate habitat use and behavior are provided.  Although data must be carefully screened to identify potential ‘dead-spots’ in the array and habitats that prevent detection (i.e., substrate, logjams), fine-scale acoustic tracking provides a tool that could greatly improve our knowledge of fish habitat use and behavior.  This information will likely lead to improved management decisions related to fish habitat.