Juvenile Chinook Salmon Survival, Travel Time, and Floodplain Use Relative to Riverine Channels in the Sacramento–San Joaquin River Delta

Abstract

Floodplains provide multiple benefits to both resident and migratory fish species, including juvenile Chinook Salmon Oncorhynchus tshawytscha, but direct comparisons of survival during migration through a floodplain versus riverine routes are scarce. The Yolo Bypass is a broad floodplain of the Sacramento River that floods in about 30% of years in response to large, uncontrolled runoff events. We analyzed data from an acoustic telemetry study conducted in winter 2016 to estimate the proportion of tagged juvenile Chinook Salmon entrained from the Sacramento River into the Yolo Bypass and their spatial distribution within the Yolo Bypass. In addition, we compared survival and travel time of Chinook Salmon that migrated through the Yolo Bypass to those migrating via alternative non-floodplain migration routes at varying stages of a flood event that activated the Yolo Bypass. We found that entrainment into the Yolo Bypass ranged from 1% to 80% among different release groups, with the highest entrainment coinciding with the peak of the March 2016 flooding event. Survival for Chinook Salmon migrating through the Yolo Bypass was similar to survival of those migrating through main-stem migration routes. At the relatively high flows necessary to enable flooding of the Yolo Bypass, survival estimates varied little among release groups and migration routes. Furthermore, mean daily survival rates for Chinook Salmon migrating through the flooded Yolo Bypass were comparable to those of fish migrating through the other non-floodplain routes. Median travel times remained relatively constant during various stages of flooding in the Yolo Bypass. This research should help managers to better understand the potential costs and benefits to floodplain restoration and routing of migrating Chinook Salmon into off-channel habitat.

Imperfect detection and misidentification affect inferences from data informing water operation decisions

“…The DCC and its two radial gates were constructed by the U.S. Bureau of Reclamation in 1951 to divert freshwater from the Sacramento River into the interior Sacramento-San Joaquin River Delta (henceforth, "the Delta") to improve the water quality of diversions to the State Water Project and Central Valley Project export facilities (State Water Resources Control Board 1978). The opening of the DCC gates alters river and tidal flows in the Estuary and has been shown to incidentally entrain up to 80% of acoustically tagged emigrating juvenile Chinook Salmon into the interior Delta (Perry et al 2010(Perry et al , 2012(Perry et al , 2015(Perry et al , 2018Romine et al 2013;Steel et al 2013;Pope et al 2021). Although entrained individuals may still complete their out-migration, studies have indicated that these individuals may experience considerably higher mortality rates based on exposure to water exportation, high temperatures, increased predation risk, and pollution (Kjelson and Brandes 1989;Brandes and McLain 2001;Newman and Brandes 2010;Buchanan et al 2013).…”

“…2013; Pope et al. 2021). Although entrained individuals may still complete their out‐migration, studies have indicated that these individuals may experience considerably higher mortality rates based on exposure to water exportation, high temperatures, increased predation risk, and pollution (Kjelson and Brandes 1989; Brandes and McLain 2001; Newman and Brandes 2010; Buchanan et al.…”

From drought to deluge: spatiotemporal variation in migration routing, survival, travel time and floodplain use of an endangered migratory fish

“…The Yolo Bypass is an engineered floodplain that is only accessible to downstream migrating fish when the Sacramento River stage exceeds the 10.2 m height of the 2.9 km long Fremont Weir. The Yolo Bypass floodplain contains valuable habitat for rearing (Katz et al 2017;Takata et al 2017) and actively migrating juvenile Chinook salmon (Johnston et al 2018;Pope et al 2021). Migrating fish that enter the Yolo Bypass avoid entrainment in the interior Delta and telemetered fish released directly into the Yolo Bypass have been demonstrated to have survival similar to those released directly into the Sacramento River (Johnston et al 2018;Pope et al 2021).…”

“…The Yolo Bypass floodplain contains valuable habitat for rearing (Katz et al 2017;Takata et al 2017) and actively migrating juvenile Chinook salmon (Johnston et al 2018;Pope et al 2021). Migrating fish that enter the Yolo Bypass avoid entrainment in the interior Delta and telemetered fish released directly into the Yolo Bypass have been demonstrated to have survival similar to those released directly into the Sacramento River (Johnston et al 2018;Pope et al 2021). During large flood events, the Yolo Bypass can carry up to four times more water than the mainstem Sacramento River (Suddeth Grimm and Lund 2016).…”

“…One major exception to the history of floodplain disconnection is the Yolo Bypass, a 24 000 ha leveed floodplain located to the west of the city of Sacramento that is designed to divert floodwaters away from urban areas, but which is only flooded in 60% of years (Suddeth Grimm and Lund 2016). Juvenile Chinook salmon rearing in Yolo Bypass have shown enhanced growth and survival (Katz et al 2017;Sommer et al 2001;Takata et al 2017) and actively migrating smolts released directly into Yolo Bypass had survival comparable to fish released into the mainstem Sacramento River (Johnston et al 2018;Pope et al 2021). However, the probability that run-of-river Chinook salmon will enter the Yolo Bypass when it is flooding and survival of fish that volitionally enter the Yolo Bypass over a range of flow conditions have not been established.…”