Methods

River stage height and weather information were recorded on most sampling days. Stage height was measured at a U.S. Geological Survey (USGS) gauge mounted on Bridge 331 and provided a relative measure of river elevation (the elevation of the bridge above sea level was not known). Stage height data were also obtained from a USGS gauge mounted on Million Dollar Bridge located at the outlet of Miles Lake. Weather information collected each day included cloud cover, precipitation, wind velocity (km/h), and wind direction.

The acoustic system and methods used in 2005 was the same system used in 2004. The transducer was deployed nearshore on the river bottom and aimed offshore, perpendicular to the river current, with the wide axis of the beam horizontal and the narrow axis vertical. The design of the transducer mount allowed adjustments in the vertical position and tilt angle of the acousic beam. An analog tiltmeter (+/- 10 deg angular range, 0.5 deg resolution) was attached to the mount, such that its tilt was aligned with the transducer. This tiltmeter, which provided a direct read of the transducer angle, allowed easy and controlled adjustment of the transducer on site without requiring access to computer data. A float switch was installed to automatically turn off the echosounder when the transducer becomes exposed to air, thereby preventing damage to its ceramic elements.

The operational setup of the camp was different in 2005. Rather than a streamside and trailer setup connected by a wireless bridge, the entire facility was consolidated onto the streamside. This location was the same as was used in the previous three years. A weatherproof aluminum box housed the echosounder, power supploy, Starband modem, and a laptop computer with 250gb external HD. Technicians resided in a large tent on a plywood platform, which also housed a desk and laptop computer. The laptop computer in the box was programmed to automatically subsample and upload relevant echogram files to a remote ftp server, while the computer in the tent was used by technicians for data analysis and to access email to send daily updates. The power supply consisted of a 12V battery bank with a capacity of 700 amp-hours, charged through a 3000 Watt Xantrex 458 inverter/charger by a honda EU2000i genset, and (2) 75 Watt solar panels. The Starband connection was used mainly for data transfer to NVE in Cordova and Aquacoustics personnel who checked the counts and the quality of the acoustic data and provided technical support to the on-site crew. Email was the primary means of communication. A satellite phone and VHF radio were available for emergencies.

To sample migrating salmon, the transducer was aimed along the river bottom. The aim of the transducer was verified using a plastic sphere (10-cm diameter) with target strength similar to an adult salmon. The sphere was lowered in front of the transducer using a fishing rod, raised 15 cm off the river bottom and then moved in- and offshore as much as water depth and current allowed. The aim of the transducer was confirmed when the target echoes were clearly visible and strong enough to qualify as salmon at least every 0.5m. Fish were sampled with a transmit power of 200W, ping rate of 14 pings / second, and a pulse length of 0.256 ms.

A wier made from rebar and construction fencing was installed app. 1m downstream of the transducer and extended into the river about 1-2 meters past the transducer. The wier kept fish from passing too close to the transducer where the acoustic beam is not coherently formed or too small to efficiently detect fish. The weir had to be close to the transducer to prevent fish from coming back inshore before having passed the transducer. In addition, several pieces of rebar were put in about 20m upstream of the transducer to direct ice floes offshore and way from the transducer. Unlike the weir, the ice deflection bars had to be at least 15m upstreamof the transducer to prevent acoustic noise created downstream of an obstacle from interfering with the sonar beam. The position of the ice deflection bars also took advantage of the natural pattern of the river current, which, at that location, hit and was deflected off the riverbank at a relatively steep angle. Technicians regularly removed debris from teh weir and the transducer mount and wiped algae growth off the transducer face.

Counts were done for the first 15 minutes of each hour using the same methodology as in 2004. Daily counts were generated by summing and expanding the 15-minute counts to hourly counts my multiplying by 4. When data collection was interrupted, counts were expanded for missing hours by taking the interpolation between the last good hour before the data gap and the first good hour after the gap.

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