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

Tyler Pilger,Doug Demko,Jackman Eschenroeder,Matthew Peterson,Andrea Fuller,Michael Hellmair

doi:10.15447/sfews.2022v20iss20art2

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.

Highlights

Freshwater resident Rainbow Trout and anadromous Steelhead are two forms of the same species (Oncorhynchus mykiss) expressing different life-history strategies (Figure 1)
The unique plasticity in life-history expression attributable to facultative anadromy requires a tailored monitoring approach that differs from Chinook Salmon monitoring
It is needed to quantify the capacity of each California’s Central Valley (CCV) river to support anadromous individuals and whether conditions can be altered to increase the expression of anadromy

Summary

Introduction

Freshwater resident Rainbow Trout and anadromous Steelhead are two forms of the same species (Oncorhynchus mykiss) expressing different life-history strategies (Figure 1). Other salmonids such as Whitespotted Char (Salvelinus leucomaenis), Brown Trout (Salmo trutta), Atlantic Salmon (Salmo salar), and Sockeye Salmon (Oncorhynchus nerka) have shown positive relationships between density and migrants (Gibson 1978; Krogius 1981; Prévost et al 1992; Morita et al 2000; Olsson and Greenberg 2004; Olsson et al 2006).

Results

Conclusion