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Methods Field Collections and Tagging. A sample of 10, relatively large (mean TL 45.3 cm) bonytail was acquired from trammel net collections made on 17 March 2003 and fitted with sonic transmitters (Table 1). A similar collection of nine, smaller (mean TL 28.4 cm) bonytail was made 08 April 2004 and fitted with sonic transmitters (Table 2). Fish were held in a floating live car for a brief time after capture, then measured (total length [TL], nearest mm), weighed (2004 only, nearest 2 gm), examined for sex and general health and condition, scanned for presence of a Passive Integrated Transponder (PIT) tag, tagged if none was present, and fitted with a sonic tag. Sonic tags were purchased from Sonotronics, Inc., Tucson, Arizona. In 2003, Model IBT-96-2 tags with a nominal 60-day life expectancy were attached with black vinyl electrician's tape to a pair of appropriately sized cable ties, and these in turn were affixed around the test fish caudal peduncle (see Mueller et al. 2003). Cable ties used on these fish were either solid or incorporated a "fusible link" of metal wire that was designed to corrode in time and allow the cable ties and tag to fall off. Model SMT-01-376 tags with a nominal 14-day life expectancy were used on smaller fish in 2004. Tags were affixed directly to the caudal peduncle using black vinyl electrician's tape. One of 10 tags malfunctioned when it was initially activated so only nine total fish were used. All fish were released near the south end of the Cibola HLP and allowed to disperse without being disturbed. Tracking. Tracking was done using one or a pair of DH-2 directional hydrophones, an omni-directional hydrophone (DH-2 with shield removed), USR- 5W ultrasonic receiver, and either headphones or external speakers. Additional shielding comprised of 6.4-mm neoprene sheeting was affixed to the directional hydrophones to reduced interterence from extraneous signals and increase directional specificity. Hydrophones were mounted on 2-m long x 12.7-mm diameter PVC poles, and directional ones were fitted with a horizontally mounted Suunto A-30L magnetic compass that was aligned with directional hydrophone such that compass bearing of an incoming signal could be approximated within about 30 degrees. Tracking was performed utilizing three different protocols. First, to obtain directional data, listening stations were established at two fixed sites, one at the north end of the high levee, the other on a small spit at the northern end of the river levee (see Fig 1). Nominally, simultaneous readings of fish number (pulse code) and compass bearing were to be taken at 15-minute intervals at each site beginning approximately at sunset and extending until dawn. Additional directional readings were taken from each listening station but these were not temporally synchronized so as to be simultaneous. Second, to acquire "point 2