Survival Estimates for Migrant Yearling Chinook Salmon and Steelhead Tagged with Passive Integrated Transponders in the Lower Snake and Lower Columbia Rivers, 1993–1998

Abstract

Precise, up-to-date survival estimates for salmonids that migrate through reservoirs, hydroelectric dams, and free-flowing sections of the Snake and Columbia rivers are essential to develop effective strategies for recovering depressed stocks. To provide this information, survival was estimated for yearling chinook salmon Oncorhynchus tshawytscha and steelhead O. mykiss with passive integrated transponder (PIT) tags that migrated through Snake River dams and reservoirs from 1993 through 1998. A multiple-recapture model for single release groups was used to estimate survival from detections of PIT-tagged fish at dams. The stretch of river over which survival was estimated varied between years, depending on the release site, the number of dams with the capability to detect and rerelease PIT-tagged fish back to the river, the total number of fish marked, and the efficiency of detecting PIT-tagged fish at each dam. Precision of survival estimates varied with the number of fish PIT-tagged and released and the amount of spill at dams with PIT-tag detectors. When spill levels were high, detection probabilities were lower, as was precision. Mortality at bypass outfall sites was not significant at any Snake River dam investigated. Estimated annual average per-project (combined reservoir and dam passage) survival ranged from 86% to 94% for yearling chinook salmon and from 88% to 92% for steelhead. Survival estimates were higher for both species in years when spill was used specifically to pass fish through nonturbine routes. Over the same stretches of river in years with similar flow conditions from 1970 through 1975, per-project survival estimates typically averaged 57-71% for yearling chinook salmon and 77-90% for steelhead. From 1993 to 1998, survival estimates for fish released from Snake River basin hatcheries to the Lower Granite Dam tailrace indicated that substantial smolt mortality occurred before fish entered the hydropower system. For each hatchery, estimated survival varied each year, and estimates from different hatcheries to Lower Granite Dam varied inversely with the distance fish traveled.

Survival Estimates for the Passage of Spring-Migrating Juvenile Salmonids through Snake and Columbia River Dams and Reservoirs, 2008.

“…When estimates for a particular river section or passage route were available from more than one release group, the estimates were often combined using a weighted average (Muir et al 2001a). Weights were inversely proportional to the respective estimated relative variance (coefficient of variation squared).…”

“…Evaluations using paired releases of PIT tagged smolts into the bypass and tailrace at each dam found little or no evidence of post-detection mortality (Muir et al 2001a). However, no such evaluation has been conducted at John Day Dam to test this assumption, partly because no mortality was found experimentally at upstream dams, and partly because the lack of sufficient PIT-tag detection capabilities downstream from John Day Dam would require prohibitively large sample sizes.…”

“…From 1993 through 2007, the National Marine Fisheries Service (NMFS) estimated survival for these stocks using detections of PIT-tagged (Prentice et al 1990a) juvenile salmonids passing through Snake River dams and reservoirs Muir et al , 1996Muir et al , 2001aMuir et al ,b, 2003Smith et al , 2000aSmith et al ,b, 2003Smith et al , 2006Hockersmith et al 1999;Zabel et al , 2002Faulkner et al , 2008. In 2008, NMFS completed the sixteenth year of the study.…”

Effects of Passive Integrated Transponder Tags on Smolt‐to‐Adult Recruit Survival, Growth, and Behavior of Hatchery Spring Chinook Salmon

“…More sophisticated individual-based models for data analysis were also developed (Burnham et al 1987) and applied, using PIT tags, to monitor juvenile salmonid survival and migration timing in the Columbia River basin (Skalski et al 1998;Muir et al 2001;Budy et al 2002). More recently, PIT tags have been used to estimate adult salmonid survivals in the Columbia River (Berggren et al 2003(Berggren et al , 2005Williams et al 2005;Copeland et al 2007).…”

Monitoring and Evaluation of Smolt Migration in the Columbia Basin : Volume XVI : Survival and Transportation Effects for Migrating Snake River Hatchery Chinook Salmon and Steelhead: Historical Estimates from 1996-2003.

“…Some researchers (e.g., Bouwes et al 1999) concluded that passing a dam by the bypass system has a negative effect on survival, in contradiction to the CJS assumptions. On the other hand, Muir et al (2001) found no significant effect of upstream detection (bypass) on downstream juvenile survival and detection for migrating yearling Chinook salmon and steelhead from 1993 through 1998. Also, Smith et al (1998) found no significant effect on downstream juvenile survival and detection of delayed migration caused by passing a dam through the bypass system.…”