Joseph H. Vinarcsik¹, Kara E. Jaenecke¹, Matthew S. Morris³, Paul J. Bentley², Gabriel T. Brooks², Adam F.P. Palik¹.

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

Since 1995, NOAA Fisheries has operated Passive Integrated Transponder (PIT) tag detection systems in the Columbia River estuary near Jones Beach (rkm 75). This location serves as the furthest downstream interrogation site on the mainstem Columbia. Detection data contributes to multiple studies throughout the basin, with primary emphasis on completing juvenile salmonid hydrosystem survival estimates to Bonneville Dam. To detect PIT-tagged outmigrating salmonid smolts in 2023, this location used three methods of interrogation: the long-running towed PIT trawl operation, a towed flexible antenna array, and several stationary autonomous detection sites installed on pile dikes. Here we describe the towed methodologies used in 2023 and their contribution to estuary detection.

The towed PIT trawl has undergone few alterations in the last 15 years. It utilizes a 91.5 meter wide trawl net towed upstream by two 41 foot Coast Guard Cutters in a pair trawl formation. The trawl net constricts into a 2.6 by 3.0 meter fish passage corridor containing a front and rear antenna array (each antenna consisting of three parallel antennas).

The towed flexible antenna array was developed in 2012 to determine the feasibility of towed detection without a trawl net. The system used in 2023 was composed of eight 6.1 by 2.4 meter horizontally oriented flexible antennas and did not use a net to focus fish towards the antennas. It was towed by a 24 foot pilot house vessel and a 38 foot landing craft that deployed and retrieved the array from a mechanical net-reel. Advantages of this system included no potential for incidental take of salmonids (and therefore no permitting requirements), smaller vessels and crew sizes, and operation in areas inaccessible to the PIT trawl.

During our sampling season the PIT trawl detected 9,754 PIT-tagged fish, of which 41% were Chinook, 7% were coho, 46% were steelhead, 4% were sockeye, less than 1% were cutthroat trout, and 2% were unknown species. During the same period the towed flexible antenna array detected 2,169 PIT-tagged fish, of which 9% were Chinook, 8% were coho, 80% were steelhead, 1% were sockeye, less than 1% were cutthroat trout, and 2% were unknown species. 

Over the next two years we will continue modifying the towed flexible antenna array and sample concurrently with both towed systems alongside our stationary pile dike sites to streamline PIT-tagged juvenile salmonid detection in the Columbia River estuary.