Tag effects on prespawn mortality of Chinook Salmon: A field experiment using PIT tags, radio transmitters, and untagged controls

Prespawn Mortality of Spring Chinook Salmon in Three Willamette River Populations

“…Although our sampling methodology was spatially and temporally consistent among years and streams (see Naughton et al. 2018b), the limited frequency of surveys (about 1–2 times/week) may have also increased the risk of carcass loss due to scavenging.…”

“…Although there was considerable variability in PSM among tag groups across years, a thorough statistical evaluation indicated no evidence of a significant tagging effect on PSM in Fall Creek or the NFMF (Naughton et al. 2018b).…”

“…Year and composite condition score were treated as categorical variables. We did not include tag type in the model comparison because Naughton et al (2018b) previously assessed relationships among PSM and tagging (PIT tag only, PIT tag + radio transmitter, or no tag) in the Fall Creek and NFMF data sets and found only small or inconsistent effects.…”

“…In contrast, low-discharge conditions may have contributed to the low recovery rates in 2014 and 2015 due to an apparent increase in scavenged carcasses. Although our sampling methodology was spatially and temporally consistent among years and streams (see Naughton et al 2018b), the limited frequency of surveys (about 1-2 times/week) may have also increased the risk of carcass loss due to scavenging.…”

“…A description of the Foster Dam fish facility and how adult Chinook Salmon were collected, sorted, and anesthetized was reported previously (DeWeber et al 2017;Naughton et al 2018a). Similarly, salmon collection and processing details at the Fall Creek and Dexter Dam fish facilities were described by Naughton et al (2018b). Salmon from all populations had to first migrate through the Willamette River main stem, which flows through a combination of dense urban areas (e.g., Portland, Salem, and Eugene-Springfield, Oregon) and irrigated agricultural lands.…”