Feasibility Study fo PIT tagging juvenile summer/fall Deschutes Chinook

The goal of this project was to PIT tag 20,000 juvenile fall Chinook in the Deschutes River while minimizing mortality due to handling and tagging to determine the feasibility for tagging large numbers of fish for future study design development. With 19,901 juvenile fall Chinook PIT tagged and a short-term mortality rate of 0.3%, this field season was considered a success. total of 19,901 juvenile fall Chinook were PIT tagged from May 24, 2011 through June 14, 2011. Both 9 mm (9,947 fish tagged) and 12 mm (9,954 fish tagged) tags were used. From 5/31/2011 to 6/9/2011, 45 juvenile fall Chinook died during PIT tagging, which was 0.3% of the tagged fish during that time period (15,733 fish). Short-term tag retention was documented from 5/31/2011 through 6/8/2011, which was 100% and included 14,890 fish.

Average length of all fish tagged (19,903) was 61mm (Figure 2). In 2011, juvenile fall Chinook averaged 59 mm fork length in May and 61 mm fork length in June. A total of 550 juvenile Chinook were weighed and measured during the study period (Figure 3). Average of those weighed and measured was 53 mm (range 36 to 90 mm fork length) and 1.8 g (range 0.3 to 7.7 g). Average condition factor for 550 juvenile fall Chinook was 1.2.

There were 227 recaptured tagged fish. Fish were recaptured from 3 to 10 days after initial tagging (average 5.2 days). Of the recaptured fish, average specific growth rate was 0.54 mm/d (average fork length 57.9 mm or about 1% per day). There were 17 fish with negative growth rates and 19 fish with zero growth rates. Daily average water temperatures during the tagging period ranged from 11°C to 13°C (Figure 4).

As of September 25, 2012, a total of 448 fall Chinook PIT tagged in the Deschutes River during spring 2011 were detected at PTAGIS interrogation sites between June 9, 2011 and September 25, 2012. Of the 448 fall Chinook detected at interrogation sites, it appeared that 424 were outmigrants and 24 were upstream migrants. Five of the interrogator sites were within Bonneville Dam and one was in the Columbia River estuary. Of the five interrogator sites at Bonneville Dam that detected juvenile fall Chinook PIT tagged in the Deschutes River in 2011, two detect downstream migrants (Bonneville Dam Powerhouse 2 Juvenile Bypass System and Bonneville Dam Powerhouse 2 Corner Collector), in which 421 were detected. Three juvenile outmigrants were detected in adult fish ladders (Bradford Island Adult Fishway, Washington Shore Adult Fishway and Adult Fish Facility, Washington Shore Adult Fishway Vertical Slots). Outmigrants passed through downstream migrant facilities at Bonneville Dam between June 9 and August 26, 2011.

Fish are detected in the estuary by the Columbia River Estuary Trawl Detector. This is a surface trawl with an antennae fixed to the cod end of the net (2.6 m wide x 3 m tall fish passage tunnel) enabling the fish to pass through the system unhandled (PIT Tag Interrogation Site
Operations & Maintenance accessed September 12, 2012; http://www.ptoccentral.org/cgi-bin/os_dates.cgi?OS=TWX#). In 2011, the estuary trawl detector was operated from March 22 to July 1 between rkm 61 to 83. Four PIT tagged juvenile Chinook were detected by the Columbia River Estuary Trawl Detector between June 20 and June 29, 2011.

Of the 424 outmigrants detected at interrogator sites, 308 were implanted with 12.5 mm PIT tags and 116 had 9 mm tags. Those with 12.5 mm tags were detected at a rate 2.6 times that of the 9 mm tags, 3.1% (308/9,954) and 1.2% (116/9,947), respectively.

Research on native juvenile fall Chinook in the Deschutes River will inform fisheries managers of specific life history and developmental stage data on this stock, such as length at time (and how this may change with thermal regime post-select water withdrawal tower at Pelton-Round Butte Hydrologic Complex), and timing of migration into the Columbia River from PIT tag arrays at Bonneville and The Dalles dams and the antenna at the mouth of the Deschutes River. Tissue samples collected from juveniles during PIT tagging may indicate changes in genetic markers with the re-establishment of the historic thermal regime in the Deschutes River. Potential exists for experimenting with estimating abundance of returning adult Chinook that were PIT tagged as juveniles and detected at Bonneville Dam and the mouth of the Deschutes River as an alternative to the current mark-recapture/aerial redd count method. After PIT tag fall Chinook begin returning, data on return timing will be available from the antenna sites mentioned and may be useful for managing fisheries at the mouth of the Deschutes River.