Counting the Parts to Understand the Whole: Rethinking Monitoring of Steelhead in California’s Central Valley

Abstract

Steelhead (Oncorhynchus mykiss expressing an anadromous life history) in the Sacramento and San Joaquin rivers and their tributaries in California’s Central Valley (CCV) belong to a Distinct Population Segment (DPS) that is listed as threatened under the US Endangered Species Act. Although contemporary management and recovery plans include numerous planned and ongoing efforts seeking to aid in DPS recovery—such as gravel augmentation, manipulation of spring flows, and restoration of rearing and spawning habitat—a paucity of data precludes the possibility of evaluating the effect of these actions on populations of Steelhead in CCV streams. Knowledge gaps relating to historic and current abundance, population-specific ratios of resident and anadromous life-history expression, and the influence of hatchery-reared fish remain largely unaddressed. This is partly a result of aspects of Steelhead biology that make them difficult to monitor, including the multitude of factors that contribute to the expression of anadromy, polymorphic populations, and migration periods that coincide with challenging field conditions. However, these gaps in understanding are also partly the result of an institutional focus on Chinook Salmon (Oncorhynchus tshawytscha) and a pervasive notion that actions benefiting Chinook populations will also benefit Steelhead populations. To evaluate these gaps and to suggest approaches for assessing DPS recovery actions, we review available data and existing monitoring efforts, and consider the actions necessary to inform the development of targeted O. mykiss monitoring programs. Current management and recovery goals focus on abundance estimates of Steelhead only, yet current monitoring is insufficient for reliable estimates. We argue that a reallocation of monitoring resources to better understand the interaction between resident O. mykiss and Steelhead would provide better data to estimate the vital rates needed to evaluate the effects of recovery actions.

Genetic parentage reveals the (un)natural history of Central Valley hatchery steelhead

“…Within all CCV steelhead hatchery programs, the RR genotype associated with expression of faster development and residency (Pearse et al, 2019;Rundio et al, 2021) was found at low frequencies, consistent with previous observations that southern O. mykiss populations below barriers to anadromy possess high frequencies of the A haplotype at Omy05, particularly in the CCV (Abadía-Cardoso et al, 2019;Eschenroeder et al, 2022;Leitwein et al, 2017;Pearse et al, 2019;Pearse & Campbell, 2018). In addition, Omy05 genotype frequencies significantly deviated from HWE in two programs (FRH and NH).…”

“…The CCV contains the Sacramento‐San Joaquin River system, a highly impacted region that occupies the central part of California (Figure 1 ). This low‐elevation area has warmer seasonal temperatures compared with northern O. mykiss habitats (Eschenroeder et al., 2022 ; McEwan, 2001 ). Landscape and hydrograph alterations from dams built over more than a century have reduced access to over 80% of previous salmonid spawning grounds and homogenized temperature and flow profiles, contributing to decreased numbers of anadromous steelhead (Eschenroeder et al., 2022 ; He & Marcinkevage, 2017 ; Lindley et al., 2006 ).…”

“…Thus, the CCV study system provides an excellent opportunity to compare variation in life history traits among different genetic lineages now exposed to similar environmental conditions. Furthermore, California experienced an intense drought between 2012 and 2016 (Eschenroeder et al., 2022 ; Herbold et al., 2018 ), as well as a marine heatwave in 2015–2016 which severely impacted the ocean conditions experienced by salmonids (Di Lorenzo & Mantua, 2016 ; Free et al., 2023 ), providing an additional opportunity to investigate shifts in life history trait patterns in response to a sudden environmental change.…”

A meta‐analysis and model comparison of juvenile salmon growth across different habitat types

“…Studies have also documented that artificially supplementing riverine habitat with food may impart a growth benefit (Boughton, Gibson, Yedor, & Kelley, 2007). As differential growth across habitats is relatively common in fish in a broad range of environments, our methods are broadly applicable and could be applied to numerous systems to investigate the differential growth between habitats, including river/ocean life histories for steelhead/ rainbow trout (Eschenroeder et al, 2022), time remaining on spawning grounds post spawning for sturgeon (Moser et al, 2016), warm water habitat for cold water river fish (Armstrong et al, 2021), mangrove habitats (Laegdsgaard & Johnson, 2001), lake bottom sediment type (Bowen, 1984), and so forth.…”

Estimates of Fall-run Chinook Salmon Escapement in Two San Joaquin River Tributaries from Device-based and Survey-based Methods

“…Pairing the counting device with photographs of passage events allows us to validate 100% of passages, thus minimizing any potential for estimation bias due to non-fish objects or other fish species triggering the devices (Putt et al 2022). Steelhead do occur in the Stanislaus and Tuolumne rivers, although infrequently (Eschenroeder et al 2022), and photographs from the device are sufficient to distinguish them from Chinook Salmon. Lastly, the narrow width of the device swim channel (30 cm) and the sensitivity of the infrared beams make it possible to detect and count individuals passing downstream through the device, which are then subtracted from upstream counts for total passages.…”