Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 9090
Title: Detection of PIT-tagged juvenile salmonids migrating in the Columbia River estuary, 2016
Author/Editor: Matthew S. Morris, Alexander J. Borsky, Paul J. Bentley, Lindsey N. Webb, Benjamin P. Sandford
Publication Year: 2017
Publisher: National Marine Fisheries Service
Contracting Agency: Bonneville Power Administration. Portland, Oregon
Contract Number: 46273 RL58
Project Number: 1993 029 00
Keywords: PIT-tag detection, trawl, estuary, Chinook salmon, steelhead, sockeye,

In 2016, we continued a multi year study in the Columbia River estuary to detect juvenile Pacific salmon Oncorhynchus spp. marked with passive integrated transponder (PIT) tags.  Fish were detected using a surface pair trawl with a matrix of rectangular detection antennas fitted into the cod-end.

This configuration relied on trawl net wings to guide fish toward the cod end of the trawl, where they would come within detection range of the antennas.  Entrained fish were able to exit the trawl safely, without capture or handling.  We deployed the trawl in the Columbia River navigation channel between river kilometer (rkm) 66 and 84 and sampled for a total of 829 h.

During this period, we detected 12,165 PIT tagged juvenile salmon, of which 16% were wild, 4% were unknown, and 80% were of hatchery origin.  Species composition of detected fish was 43% spring/summer Chinook, 3% fall Chinook, 43% steelhead, 2% sockeye, 6% coho, less than 1% cutthroat trout, and 3% unknown. 

    In 2016, we continued development of a flexible antenna array that could be towed behind two small vessels to detect juvenile salmon without a net.  Objectives of this development effort are to simplify logistics, increase sample efficiency, and reduce the cost of sampling PIT-tagged fish in the estuary.

For these tests, the flexible antenna array was configured with six rectangular antennas each housed in 1.9 cm diameter flexible PVC hose.  The flexible antenna system can utilize up to 12 antennas, but six were used because of limited resources.  Sampling cruises to test the flexible antenna array were conducted simultaneously with deployments of the matrix trawl system.  We compared detection efficiency between the two systems to evaluate the feasibility of transitioning entirely to the flexible system in future years.

The flexible antenna system detected a total of 549 fish across 21 d of operation in 2016 (78.2 h total).  Of these total detections, 14% were Chinook, 79% steelhead, 4% coho, less than 1% sockeye, and 3% unknown species.  We sampled the flexible and matrix systems simultaneously on 10 d.  Daily ratios of mean detection rate (fish/h) between the two systems were calculated for each concurrent deployment.  Over the 10 d of simultaneous deployment, the overall mean ratio of detection rates for the flexible vs. the matrix trawl systems was 60%.

Juvenile steelhead were detected in disproportionately high numbers in the flexible antenna system, comprising 78% of total detections—more than double the proportion of steelhead detected in the matrix trawl (35%).  This discrepancy was likely due to the shallow sample depth of the flexible antenna system compared to the matrix trawl system (3.0 vs. 5.0 m).  We concluded that the relatively shallow sample depth of the flexible antenna system likely allowed Chinook salmon to pass below the array without being detected.

After the spring migration season, we tested multiple orientations and configurations of a six-antenna flexible array with the objective of increasing sample depth.  Testing confirmed the feasibility of re-configuring antennas to obtain a sample depth of 6.0 m without sacrificing electronic performance.  We plan to use the new configuration in 2017 sampling and expect that it will increase detections of Chinook salmon.

Theme: Recovery and rebuilding of marine and coastal species
Foci: Characterize the population biology of species, and develop and improve methods for predicting the status of populations.