Response of juvenile Chinook salmon to managed flow: lessons learned from a population at the southern extent of their range in North America

Abstract

Fourteen years (1996–2009) of juvenile Chinook salmon, Oncorhynchus tschawytscha (Walbaum), migration data on the regulated Stanislaus River, California, USA were used to evaluate how survival, migration strategy and fish size respond to flow regime, temperature and spawner density. An information theoretic approach was used to select the best approximating models for each of four demographic metrics. Greater cumulative discharge and variance in discharge during the migration period resulted in higher survival indices and a larger proportion of juveniles migrating as pre‐smolts. The size of pre‐smolt migrants was positively associated with spawner density, whereas smolt migrant size was negatively associated with temperature and positively associated with discharge. Monte Carlo techniques indicated high certainty in relationships between flow and survival, but relationships with juvenile size were less certain and additional research is needed to elucidate causal relationships. Flow is an integral part of the habitat template many aquatic species are adapted to, and mismatches between flow and life history traits can reduce the success of migration and the diversity of migratory life history strategies. The analyses presented here can be used to assist in the development of flow schedules to support the persistence of salmon in the Stanislaus River and provide implications for populations in other regulated rivers with limited and variable water supply.

Survival of Juvenile Fall‐Run Chinook Salmon through the San Joaquin River Delta, California, 2010–2015

“…These calculations assume juvenile survival from the tributaries to the Delta is 1.0, which is not the case (Brandes and McLain ; Zeug et al. ). Additionally, survival through the bays can be lower than survival through the Delta itself for late‐fall‐run Chinook Salmon (Michel et al.…”

“…Using a low-end Delta juvenile survival value of 0.025, SAR of 0.02 requires post-Delta survival of 0.80. These calculations assume juvenile survival from the tributaries to the Delta is 1.0, which is not the case (Brandes and McLain 2001;Zeug et al 2014). Additionally, survival through the bays can be lower than survival through the Delta itself for late-fall-run Chinook Salmon (Michel et al 2015), and Lindley et al (2009) concluded that ocean conditions contributed heavily to the fall-run salmon fishery collapse in 2007 and 2008.…”

Patterns and magnitude of flow alteration in California, USA

“…This is the first study to comprehensively assess flow alteration in California's gaged streams. Previous efforts to characterise patterns of hydrologic modification in the state have focused on individual rivers (e.g., Brown, ; Brown & Ford, ; Kiernan et al ; Zeug, Sellheim, Watry, Wikert, & Merz, ), specific regions (Brown & Bauer, ; Carlisle, Nelson, & May, ; Kondolf & Batalla, ) and dam‐regulated rivers in the state (Grantham et al., ). In addition to an expanded spatial scale, this effort is the first to simultaneously characterise the type (inflated or deflated), frequency and magnitude of alteration for several flow metrics.…”

“…Missing data in the bar chart indicated by * and zero per cent non-native fish indicated by 0 the dry region and direct discharges of wastewater and run-off to urban streams, which has been documented in California (White & Greer, 2006) and other Mediterranean-climate regions of the world (Carey & Migliaccio, 2009 This is the first study to comprehensively assess flow alteration in California's gaged streams. Previous efforts to characterise patterns of hydrologic modification in the state have focused on individual rivers (e.g., Brown, 2000;Brown & Ford, 2002;Kiernan et al 2012;Zeug, Sellheim, Watry, Wikert, & Merz, 2014), specific regions (Brown & Bauer, 2010;Carlisle, Nelson, & May, 2016;Kondolf & Batalla, 2005) and dam-regulated rivers in the state (Grantham et al, 2014). In addition to an expanded spatial scale, this effort is the first to simultaneously characterise the type (inflated or deflated), frequency and magnitude of alteration for several flow metrics.…”

Managing for Salmon Resilience in California’s Variable and Changing Climate

“…Coordinated operation of reservoirs, pumps, and canals removes as much as 7.4 billion cubic meters of freshwater from the San Francisco Bay-Delta estuary each year. Timing and volumes of reservoir releases control much of salmon survival downstream (Zeug et al 2014). Native landscapes have been almost entirely supplanted by urban and agricultural landscapes (Figure 4).…”