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4 I I I I I I I I I I I I ;, I :.1 I I I I Surveys were conducted each week by boat using a directional hydrophone. The San Juan Arm of Lake Powell is narrow and surveyors stopped at 500-800 m intervals along the channel and in every cove and side canyon to check for signals. Stream sections were monitored while floating downstream. A GPS grid pattern was designed for Lake Mohave to accommodate its 5 kIn width. Waypoints or "listening stations" (71) were spaced 1,600 m apart to standardize monitoring locations and effort (Figure I). After the second week we increased the number of stops to over 125 locations, and bimonthly, we visited each cove and intensified (100 m intervals) our monitoring of flooded, shoreline vegetation. When a fish was located the following information was recorded: date, time of day, location determined using GPS and/or maps, relative depth, distance from the shoreline, vegetation, cover type, and hydraulic characteristics (flowing versus slack). Location was recorded in latitude and longitude, river mile, and marked on a map. Water depth was determined visually or by using a fathometer, shoreline distance was estimated (<10 m, 10-50 m, >50 m). Surveys continued for 100 days. We attempted to recapture fish 80 days into the study to assess the attachment technique and to remove the transmitters. Trammel nets were set-on fish found in shallow, calm habitats. RESULTS Tracking Lake Powell Surveys at both study locations began the morning following release. Initially Lake Powell surveys were conducted between RK 51 to RK 85, a distance of roughly 34 kIn. At the time of release, fish access upstream of RK 85 was physically blocked by a 3 m high water fall. It was impossible to discern individual signal codes when fish were first released due to garbled signals. No cove held fish were detected outside of the enclosures during their period of captivity. All fish had left their release sites after 5 days but many remained in the Castle Creek Canyon complex. Initial contact was made with 23 of the 28 fish (Figure 2). Fish gradually dispersed, with all but three moving upstream. By June 10, the reservoir had risen to a point where the falls was inundated and could be negotiated safely by boat. Rising waters also inundated hundreds of hectares of flooded tamarisk which was impossible to monitor effectively. Submerged vegetation absorbed the sonic signal significantly reducing the signal range in some cases <50 m. During this period the water falls was also inundated and surveys were extended upstream (20 kIn) to Slickhorn Rapids (RKI06) and during the week of August 12, two boat crews searched the entire 106 kIn reach between the confluence of the San Juan and Colorado rivers (RK 0) to Slickhorn Rapids (RK 106). Although the search effort was extensive, no additional fish were found.