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Comparing Stationary and Towed PIT Interrogation Methods for Detecting Juvenile Salmonids in the Lower Columbia River Estuary

Kara E. Jaenecke1, Joseph H. Vinarcsik1, Matthew S. Morris2, Paul J. Bentley3, Gabriel T. Brooks3, Adam Palik1

  1. Ocean Associates, Inc.  Under contract to Northwest Fisheries Science Center.  National Marine Fisheries Service.  NOAA.  520 Heceta Place, Hammond, Oregon 97121.
  2. Astor Environmental LLC. Under contract to Northwest Fisheries Science Center.  National Marine Fisheries Service.  NOAA.  520 Heceta Place, Hammond, Oregon 97121.
  3. Fish Ecology Division.  Northwest Fisheries Science Center.  National Marine Fisheries Service. NOAA.  520 Heceta Place, Hammond, Oregon 97121

For the last 25 years, the NOAA PIT trawl has served as the primary source of PIT interrogation in the Columbia River estuary as a means to estimate survival of out-migrating juvenile salmonids through the hydropower system. In 2023, we applied two additional interrogation methods to assess the efficacy of three separate systems in the lower estuary: the long-running PIT trawl, an experimental towed flexible antenna array, and four autonomous stationary sites installed along pile dikes.

Since 2011, we have operated a stationary PIT interrogation site with antennas installed along pile dike 43.30 (“PD7” in PTAGIS) near RKM 70 in the Columbia River.  In 2022, we expanded to an additional site along training dike 42.93 (“PD6” in PTAGIS), located just downstream of PD7.  We found that placement and orientation of both antennas and pile dikes relative to river flow were key to determining detection rates of juvenile salmonids: antennas deployed along the upstream face of dikes were more effective at detecting juvenile salmonids compared to downstream antennas, and the installed along a training dike oriented ~45 degrees to flow (PD6), detected juvenile salmonids at nearly tenfold the rate of the array installed along a spur dike (PD7), which was oriented perpendicular to river flow.  Further, PD6 detected roughly 1/3 the volume of juvenile salmonids detected by the PIT trawl in 2022, though detections were biased at a ratio of nearly 3:1 juvenile Chinook salmon to steelhead compared to an almost equal distribution of these species detected on the trawl.

In 2023, we used this knowledge to guide new site expansion and installed four pile dike interrogation sites between RKM 58 and 80.  Sites PD5, PD6, and PD8 were installed along training dikes similar in both structure and orientation to flow, while PD7 remained at the spur dike.  During peak migration season, each site operated 4-6 antennas distributed along the upstream face of the dikes. To overcome species bias, we redesigned our towed flexible antenna array in 2023 by orienting antennas horizontally instead of vertically, to mimic earlier tests that showed a shallower depth increased the percentage of juvenile steelhead detections.

During the 2023 spring migration season, these three interrogation methods detected a combined total of 24,679 PIT tagged fish: 9,754 detected with the PIT trawl, 2,169 from the towed flexible antenna system, and 12,756 from the stationary pile dike systems.  Overlap across all methods was minimal, with only 2% of all detections recorded on more than one site. Combined tag data collected from the towed flexible system and pile dikes sites were similar to the PIT trawl in detection rate, species composition, and basin of origin.  Data collected from these experimental sites in 2023 exemplify the high potential of autonomous systems to supplement detection of juvenile salmonids in the estuary. Further development and expansion of these newer systems will boost lower river detection rates and provide data to support survival estimates using efficient, cost-effective, and low-impact methods.