Impact of smallmouth bass predation on subyearling fall Chinook salmon over a broad river continuum

Abstract

Smallmouth bass (Micropterus dolomieu) predation on subyearling fall Chinook salmon (Oncorhynchus tshawytscha) was examined in the Snake River (USA) to identify seasonal and habitat-related changes in bass diets, and associated subyearling consumption and loss in various riverine and impounded reaches. Smallmouth bass diets reflected opportunistic foraging that at times showed predation on subyearlings is influenced by the consumption of other prey such as crayfish, sand roller (Percopsis transmontana), and smaller invertebrates. Estimated loss of subyearlings was influenced by bass abundance and consumption rates. The highest bass abundances (> 1,000 bass/river kilometer) were observed in the upper reach of Hells Canyon early in April and May, and in Lower Granite Reservoir. Peak consumption rates of subyearlings (≥ 0.12 subyearlings/ bass/day) occurred in the upper reach of Hells Canyon during May and in most reservoir reaches in June. Predation losses accumulated evenly along the river continuum from riverine to reservoir habitats. We estimated that 869,371 subyearlings could be lost to smallmouth bass predation between riverine production areas and Lower Granite Dam in a given year. To provide a context for this estimated loss, we provide an illustration of its potential effect on the adult population. Assuming no juvenile mortality occurred downstream of the dam and depending on smolt-to-adult return rates, this represented up to 3.9-16.0% of the potential adult run that could have returned to Lower Granite Dam had no subyearling predation by smallmouth bass occurred upstream of the dam. Although this study was limited by a number of assumptions and constraints, it does provide an illustration of how predation affects juvenile and adult salmon loss over a broad, changing river landscape.

The Importance of Phenology and Thermal Exposure to Early Life History Success of Nonnative Smallmouth Bass in the Yellowstone River

“…2015; Tiffan et al. 2020), managers will have to consider the tradeoffs of controlling adults and juveniles near the upstream extent versus the uncertainty of future spread and amplification of their consumptive impacts.…”

“…For example, Smallmouth Bass introductions in tributaries to the Columbia River ultimately resulted in invasions and substantial predation on juvenile salmonids across most of the lower and middle Columbia River basin, wherein widespread prevention of future spread may now be challenging (Carey et al 2011;Rubenson and Olden 2020). For nonnative species that were intentionally introduced but can have unintended consequences for fish assemblages (e.g., Smallmouth Bass and Rainbow Trout Oncorhynchus mykiss; Shelton et al 2015;Tiffan et al 2020), managers will have to consider the tradeoffs of controlling adults and juveniles near the upstream extent versus the uncertainty of future spread and amplification of their consumptive impacts.…”

Integrating spatial stream network models and environmental DNA to estimate current and future distributions of nonnative Smallmouth Bass

“…Smallmouth Bass can cause significant predation mortality for ecologically and societally important native species like Pacific salmon Oncorhynchus spp. For example, Smallmouth Bass have been estimated to consume up to 35% of a Chinook Salmon O. tshawytscha smolt population as they migrate seaward, effectively reducing opportunities for fish to reach their adult life stage, where reproduction or harvest could occur (Fritts and Pearsons 2004;Sanderson et al 2009;Tiffan et al 2020). Watershed-scale Smallmouth Bass spatial distributions are strongly correlated with stream temperature, and anticipated range expansions under climate change are alarming in the context of increased potential for both predation and nonconsumptive impacts on Pacific salmon (Kuehne et al 2012;Lawrence et al 2014;Rubenson and Olden 2020;Marsha et al 2021).…”

“…2009; Tiffan et al. 2020). Watershed‐scale Smallmouth Bass spatial distributions are strongly correlated with stream temperature, and anticipated range expansions under climate change are alarming in the context of increased potential for both predation and nonconsumptive impacts on Pacific salmon (Kuehne et al.…”

Expansion of smallmouth bass distribution and habitat overlap with juvenile Chinook salmon in the Willamette River, Oregon

“…These fish are widespread in habitats of juvenile Pacific salmon Oncorhynchus spp. throughout the Pacific Northwest, United States (Carey et al, 2011; Hughes & Herlihy, 2012; Rubenson & Olden, 2019; Tiffan et al, 2016) and have been shown to be a significant predation threat (Fritts & Pearsons, 2004; Tabor et al, 1993; Tiffan et al, 2020). Interactions between smallmouth bass and juvenile salmon increase during spring and summer as water temperature warms.…”