Predation on Juvenile Salmonids by Smallmouth Bass in the Lower Granite Reservoir System, Snake River

Abstract

We estimated the consumption of juvenile salmon Oncorhynchus spp. and steelhead O. mykiss by smallmouth bass Micropterus dolomieu in the tailrace and forebay of the Lower Granite Dam and compared this consumption with that in the two major river arms of the upper Lower Granite Reservoir, Snake River, Idaho–Washington. We examined over 9,700 smallmouth bass stomachs from April through August during 1996 and 1997. Juvenile salmonids were not a major component of smallmouth bass diets by weight and number at any location in either 1996 or 1997. Of the approximately 8,600 stomach samples containing food items, only 67 had juvenile salmonid remains. Juvenile salmonids accounted for approximately 11% of smallmouth bass diets by weight in the forebay in 1996 and 5% in the Snake and Clearwater river arms in 1997, with smaller proportions at other locations. Crustaceans and nonsalmonid fishes were the dominant prey items by weight at all locations in 1996 and 1997 except for the Snake River arm in 1996, where macroinvertebrates were dominant. Monthly consumption rates (smolts/bass/d) of juvenile salmonids by smallmouth bass were highest in the forebay (0.02) in April 1996 and in the restricted zone of the forebay (0.05) in July 1997. We estimated that approximately 17,500 (1996: 6,728; 1997: 10,809) juvenile salmonids were consumed by smallmouth bass from April through August in 1996 and 1997. High flows and resulting lower water temperatures and higher turbidity in the Lower Granite Reservoir during our study probably affected salmonid predation rates by smallmouth bass. Management efforts directed at enhancing migratory conditions for juvenile salmonids (e.g., higher flows, lower water temperatures, and higher turbidity) will probably also reduce predation from smallmouth bass.

Report on the Predation Index, Predator Control Fisheries, and Program Evaluation for the Columbia River Basin Experimental Northern Pikeminnow Management Program, 2008 Annual Report.

“…The predation index is composed of two components, consumption and abundance (Miranda and Hubbard 1994;Van Den Avyle and Hayward 1999). As reported in earlier work Zimmerman 1999;Naughton et al 2004), juvenile salmonids comprised a small but consistent portion of smallmouth bass diets in the Columbia River during 2008, and the primary prey consumed by smallmouth bass continued to be sculpin. Ward and Zimmerman (1999) suggested the first evidence of any response by smallmouth bass would likely be a change in diet.…”

Using movements and diet analyses to assess effects of introduced muskellunge (Esox masquinongy) on Atlantic salmon (Salmo salar) in the Saint John River, New Brunswick

“…Muskellunge most probably consumed some Atlantic salmon smolts as do esocids in other systems (Warner et al 1968;Jepsen et al 1998), but grilse or adult salmon have a low probability of being consumed based on the isotope signatures of anadromous fishes in the SJR. Many other fish predators that are significantly more abundant in the SJR (Curry and Munkittrick 2005) can consume smolts such as striped bass, M. saxatilis (Blackwell and Juanes 1998), smallmouth bass (Naughton et al 2004), brown trout, Salmo trutta (Huntingford et al 1988), and brook charr, S. fontinalis (Mohler et al 2002). The best estimate of smolt consumption by muskellunge predicted a total of 7,400 smolts consumed downstream of the Mactaquac Dam if every muskellunge ate smolts only.…”

Effects of turbidity and risk of predation on habitat selection decisions by Fathead Minnow (Pimephales promelas)

“…Similarly, consumption of juvenile salmonids (Oncorhynchus spp.) and steelhead by Smallmouth Bass (M. dolomieu) were lower in more turbid rivers (Naughton et al 2004). Gregory and Levings (1998) concluded that higher turbidity reduced encounter and mortality rates of age-0 Pacific Salmon by piscivorous fishes.…”