Impact of smallmouth bass predation on subyearling fall Chinook salmon over a broad river continuum
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pact of smallmouth bass predation on subyearling fall Chinook salmon over a broad river continuum Kenneth F. Tiffan & John M. Erhardt & Rulon J. Hemingway & Brad K. Bickford & Tobyn N. Rhodes
Received: 10 February 2020 / Revised: 14 July 2020 / Accepted: 9 August 2020 / Published online: 24 August 2020 # Springer Nature B.V. 2020
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 K. F. Tiffan (*) : J. M. Erhardt : R. J. Hemingway : B. K. Bickford : T. N. Rhodes Western Fisheries Research Center, U.S. Geological Survey, 5501A Cook-Underwood Rd, Cook, WA 98605, USA e-mail: [email protected]
Present Address: J. M. Erhardt U.S. Fish and Wildlife Service, Idaho Fish and Wildlife Conservation Office, 276 Dworshak Complex Drive, Orofino, ID 83544, USA
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. Keywords Consumption . Diet . Snake River . Mortality . Predation
Introduction Predation is a significant source of mortality for juvenile salmon and is commonly cited as a contributing factor to the decline of anadromous salmonids in the Pacific Northwest of the United States (Sanderson et al. 2009; Carey et al. 2011). Predation on juvenile salmonids by both piscine and avian predators has been studied extensively in anadromous fish-bearing waters along the west coast of the United States and Canada (Rieman et al. 1991; Greg
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