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We quantified the percentage of PIT-tagged subyearling fall Chinook Salmon Oncorhynchus tshawytscha that were consumed by Caspian terns Hydroprogne caspia and double-crested cormorants Phalacrocorax auritus nesting on East Sand Island in the Columbia River estuary by electronically recovering PIT tags that were deposited on the bird colonies. We released 23 groups of PIT-tagged subyearling fall Chinook Salmon from hatcheries in the lower Columbia River downstream of Bonneville Dam from 2002 to 2010. Vulnerability to avian predation was compared between PIT-tagged subyearlings of two Columbia River basin stocks: tule and upriver bright (URB). Recoveries of PIT tags revealed that overall predation rates were significantly different between the tule stock (22%) and URB stock (3%); for fish that were detected as entering the lower Columbia River during the same week, predation rates also differed between stocks (tule: 21%; URB: 2%). Minimum predation rates on tule subyearlings originating from hatche...

We recovered passive integrated transponder (PIT) tags from nine piscivorous waterbird colonies in the Columbia River basin to evaluate avian predation on Endangered Species Act (ESA)-listed salmonid Oncorhynchus spp. populations during 2007–2010. Avian predation rates were calculated based on the percentage of PIT-tagged juvenile salmonids that were detected as passing hydroelectric dams and subsequently were consumed and deposited by birds on their nesting colonies. Caspian terns Hydroprogne caspia (hereafter, “terns”) and double-crested cormorants Phalacrocorax auritus (hereafter, “cormorants”) nesting on East Sand Island in the Columbia River estuary consumed the highest proportions of available PIT-tagged salmonids, with minimum predation rates ranging from 2.5% for Willamette River spring Chinook salmon O. tshawytscha to 16.0% for Snake River steelhead O. mykiss. Estimated predation rates by terns, cormorants, gulls of two species (California gull Larus californicus and ring-billed gull L. ...

From 1987 to 1992, we evaluated a fish bypass system at Bonneville Dam Powerhouse 2 on the Columbia River. The survival of subyearling Chinook salmon Oncorhynchus tshawytscha released into the system ranged from 0.774 to 0.911 and was significantly lower than the survival of test fish released into turbines and the area immediately below the powerhouse where bypass system flow reentered the river. Yearling and subyearling Chinook salmon and yearling coho salmon O. kisutch released into the bypass system were injured or descaled. Also, levels of blood plasma cortisol and lactate were significantly higher in yearling and subyearling Chinook salmon that passed through the bypass system than in fish released directly into a net located over the bypass exit. This original system was then extensively modified using updated design criteria, and the site where juvenile fish reentered the river was relocated 2.8 km further downstream to reduce predation on bypassed fish by northern pikeminnow Ptychocheilu...

We developed a surface pair-trawl system to detect juvenile Pacific salmon Oncorhynchus spp. marked with passive integrated transponder (PIT) tags as they migrate through the upper Columbia River estuary. The trawl was fitted with a detection antenna in its cod end and was deployed by two vessels. Fish entering the trawl body exit after passing by the detection antenna. Detection data were recorded by electronic components housed in a small boat tethered to the trawl. The system was modified extensively after its first deployment in 1995 and by 2001 was performing reliably under a variety of weather conditions and river flows. From 1995 to 2001 the device detected 29,699 PIT-tagged juvenile salmon. During extended daily sampling periods, we detected nearly 2% of all PIT tags previously detected at Bonneville Dam, which is located 159 rkm upstream from the study area.

Passive integrated transponder (PIT) tags implanted in Columbia River basin juvenile salmonids Oncorhyncus spp. were recovered from breeding colonies of Caspian terns Sterna caspia and double-crested cormorants Phalacrocorax auritus on Rice Island, a dredge spoil island in the Columbia River estuary. Tags were recovered to assess the relative vulnerability of different salmonid species, stocks, and rearing types to avian predators. We detected 50,221 PIT tags at the two bird colonies, mostly from juvenile chinook salmon O. tshawytscha and steelhead O. mykiss raised in hatcheries; 72% of the total tags were from the tern colony and 28% from the cormorant colony. Tagged steelhead smolts were more vulnerable to predation by both bird species than were yearling chinook salmon. More than 15% of PIT tags from steelhead smolts that were available in the estuary in 1998 were detected at the bird colonies compared with 2% of PIT tags from yearling chinook salmon. The greater vulnerability of steelhead may...

We modified 400-kHz passive integrated transponder (PIT) tag detection equipment, previously used in water, to detect PIT tags in piscivorous bird-nesting areas in the Columbia River basin. Two land-based recovery mechanisms were developed: a flat-plate antenna that was drawn over the surface of bird-nesting areas with a four-wheel-drive vehicle and a pole-mounted antenna that was passed by hand over smaller nesting areas. In 1998 and 1999, we detected more than 100,000 unique PIT tag codes by the use of the flat-plate antenna, and in 1999, we detected more than 10,000 unique PIT tag codes by the use of the pole-mounted antenna. Codes were detected for every release year since 1987, the first year that salmonids were marked with PIT tags in the Columbia River basin; however, the majority of tag codes came from juveniles marked for the 1999 migration year (>50,000 tag codes recovered). In 2000, researchers in the Columbia River basin changed to a 134.2-kHz PIT tag, in accordance with guidelines fr...

In 2008, we sampled migrating juvenile Pacific salmonids Oncorhynchus spp. tagged with passive integrated transponder (PIT) tags using a surface pair trawl in the upper Columbia River estuary (rkm 61-83). The cod-end of the trawl was replaced with a cylindrical PIT-tag detection antenna with an 86-cm-diameter fish-passage opening and two detection coils connected in series. The pair trawl was 105 m long with a 91.5-m opening between the wings and a sample depth of 4.9 m. Also during 2008, we finalized the development of a prototype 'matrix' antenna, which was larger than previous antennas by a considerable magnitude. The matrix antenna consisted of 6 coils: a 3-coil front component and a 3-coil rear component, which were separated by 1.5-m of net mesh. The fish-passage opening was 2.5 m wide by 3.0 m tall and was attached to a standard-size pair trawl net. Intermittent sampling with a single crew began on 7 March and targeted yearling Chinook salmon O. tshawytscha and steelhead O. mykiss. Daily sampling using two crews began on 30 April and continued through 14 June; during this period we detected 2.7% of all juvenile salmonids previously detected at Bonneville Dam--a measure of sample efficiency. Sampling with a singlemore » crew continued through 20 August and targeted subyearling Chinook salmon. We detected 7,397 yearling Chinook salmon, 2,735 subyearling Chinook salmon, 291 coho salmon O. kisutch, 5,950 steelhead, and 122 sockeye salmon O. nerka in the upper estuary. We deployed the matrix antenna system and the older, cylindrical antenna system (86-cm-diameter fish-passage opening) simultaneously in mid-May 2008 to test matrix detection efficiency. The cylindrical antenna system had been used successfully in 2007 and early 2008. Because distribution of migrating salmonids in the estuary changes rapidly, we felt that a tandem sampling effort between the two systems was the only way to truly evaluate comparative detection efficiency. We deployed both systems within 1 km of each other during a period of high fish densities on 13, 14, and 15 May. Detections of the matrix system surpassed those of the cylindrical system by 53% in 14 h of simultaneous sampling (total detections 716 and 339, respectively). We believe that the higher detection rate observed with the matrix system was due to fewer smolts escaping the trawl entrance and to more smolts readily passing through the larger fish-passage opening. After tandem sampling, we continued exclusive use of the matrix system for the remainder of the 2008 juvenile migration season. Mean survival rates from Lower Granite to Bonneville Dam for yearling Chinook salmon and steelhead were 42% (SE = 3.7%) and 46% (SE = 1.5%), respectively. Over 358,000 PIT-tagged salmonids were transported, and we detected 4,619 of these fish.« less