Winter habitat utilization and movement by cutthroat trout in the Snake River Near Jackson, WY 2000-2001.

Authors(s): D. Harper

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Publication Date: 0000-00-00

Type: annual report

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Abstract: Objectives The objectives of the study are to identify critical winter habitat used by cutthroat trout in the Snake River Near Jackson, WY, and to determine the patterns of movement during late fall winter. Overwintering habitat is often the limiting factor for salmonids in high elevation streams. We are trying to determine what types of habitat cutthroat trout are using during winter using radiotelemetry. We are also observing and recording the movement patterns of cutthroat trout during winter. If long distance movements are observed, this could be an indication that overwintering habitat is limited in the study area. Data on habitat use and movement will provide resource managers with additional information to make infomed decisions concerning cutthroat management. We radiotagged 30 juvenile cutthroat trout ( less than 300 cm) between Moose and Wilson WY. We also tagged 20 adult cutthroat trout ( greater than 330g) between Deadmans Landing and Moose, WY. Juvenile cutthroat habitat use and movement was monitored by floating the river 3 days per week, from November through mid-February. Findings and Status In September 2000, 30 juvenile cutthroat trout with a mean weight of 231g (range = 159-311g) were implanted with radio transmitters in the Snake River between Moose, Wyoming and the confluence of the Gros Ventre River. An additional 20 cutthroat trout with a mean weight of 478g (range = 333-772g) were implanted with radio transmitters between Deadman's Landing and the confluence of Cottonwood Creek. Starting 21 November 2000, floats were performed weekly to locate tagged fish and record habitat use of juvenile cutthroat between Moose, WY and the South Park Bridge. Tracking was concluded on 7 February 2001, when scheduled battery failure was observed. During 26 days on the river tracking fish, a total of 116 habitat measurements were recorded at the location of 23 different fish. One mortality was confirmed (located transmitter); however 5 radiotagged fish were never located during floating searches. Aerial surveys to locate tagged fish also failed to locate these 5 tagged fish between Palisades Reservoir and Jackson Lake Dam, indicating battery or programming failure with these transmitters. Habitat use by juvenile cutthroat trout appears to be similar to the habitat used by adult cutthroat trout during winter 1998/1999 and 1999/2000. Water and air temperatures were much colder however during winter 2000/2001, and frazil and anchor icing conditions were repeatedly observed. Shelf ice and ice cover over backwater pool areas was also more frequently observed during winter 2000/2001. Backwater pools were selected as overwintering habitat at 65 percent of the recorded habitat measurements. Deep run habitat was selected 34 percent of fish locations, compared with 52 percent during winter 1998/1999 and 1999/2000. This is probably a response to icing conditions displacing fish from run habitat, as anchor ice was regularly observed covering the substrate of riffle and run habitats. Ice cover was observed as the most frequently selected type of cover at fish locations (85 percent ). Movement patterns of juvenile cutthroat trout appear to be in a downstream direction, with most movement occurring following the onset of cold winter water temperatures. Preliminary analysis indicates movement ranging from approximately 500 meters, up to 30 km downstream. Only one fish moved above the location where it was captured and implanted. Adult sized cutthroat trout implanted above Moose were located by float survey on 1 November, and have been tracked by aerial survey on 27 December and 16 February. Fifteen of 20 fish (75 percent ) have not moved beyond 1 km from the location of capture, with an additional 4 fish moving beyond 1km. Two fish have moved upstream a considerable distance (12 and 21 km) with a maximum downstream distance of approximately 6 km. One tagged fish has not been located by float or aerial surveys. It appears that adult sized cutthroat do not move downstream long distances from the upper Snake River above Moose; however, additional float tracking surveys will be conducted in March to validate fish locations.

Keywords: Grand Teton National Park, animal, fish, ichthyology, Pisces, trout, cutthroat trout, Snake River cutthroat trout, Oncorhynchus clarki bouvieri, Jackson Lakehabitat, migration, radio collar, Snake River, Jackson Hole, Teton County, Salmonidae, management, Moose, Wilson, Gros Ventre River, South Park Bridge, Cottonwood Creek, mortality, Palisades Reservoir