Feeding Activity, Rate of Consumption, Daily Ration and Prey Selection of Major Predators in John Day Reservoir, 1985: Annual Report.

Technical Report · Wed Oct 01 04:00:00 EDT 1986

DOI:https://doi.org/10.2172/7109163· OSTI ID:7109163

Palmer, Douglas E

This report summarizes activities in 1985 to determine the extent of predation on juvenile salmonids in John Day Reservoir. To estimate consumption of juvenile salmonids we used the composition of the natural diet of predators and in the laboratory determined rate of gastric evacuation by predators. Salmonids were the single most important food item for northern squawfish (Ptychocheilus oregonensis) at McNary tailrace during all sampling periods and at John Day forebay during July. Salmonids accounted for 11.6% of the diet of walleye (Stizostedion vitreum vitreum) in 1985 which was about twice that found in previous years. Salmonids contributed little to smallmouth bass (Micropterus dolomieui) diet but comprised about 25% of the diet of channel catfish (Ictalurus punctatus). Composition of prey taxa in beach seine catches in 1985 was similar to 1983 and 1984 with chinook salmon (Oncorhynchus tschawytscha), northern squawfish, largescale sucker (Catostomus macrocheilus), and sand roller (Percopsis transmontana) dominating the catch at main channel stations and crappies (Pomoxis spp.) and largescale sucker dominating at backwater stations. Preliminary results of beach seine efficiency studies suggest that seine efficiency varied significantly among prey species and between substrate types in 1985. Results of digestion rate experiments indicate that gastric evacuation in northern squawfish can be predicted using water temperature, prey weight, predator weight and time. 19 refs., 19 figs., 13 tabs.

• Research Organization: Fish and Wildlife Service, Cook, WA (USA). Willard Field Station
• DOE Contract Number: AI79-82BP34796
• OSTI ID: 7109163
• Report Number(s): DOE/BP-34796-2; ON: DE87002972
• Country of Publication: United States
• Language: English

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ANIMAL GROWTH
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AQUATIC ORGANISMS
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