Research on fish movement and habitat use in large tropical rivers is urgently needed to protect fisheries that are a primary source of protein for millions of people. In this pilot study, acoustic telemetry was used to monitor movements of wild catfishes in a 94.6 rkm reach of Mekong River, where it functions as the border between Thailand and Lao People’s Democratic Republic (PDR). Twenty fish were tagged and released in May 2006 and monitored through May 2007 with 17 fixed-site acoustic receivers. Ten receivers had detection probabilities ranging from 0.67 to 1.00, and five receivers had detection probabilities of 0.50 or less. Detection probability was not correlated with river width. Eighteen (90%) of the tagged fish were detected by at least one receiver. Monitoring durations of individual fish ranged from 0.1 to 354.4 days. The longest total movement was 88.3 rkm, while the longest upstream movement was 52.1 rkm. Movement rates ranged from 0.1 to 156.7 rkm/d. This work provided preliminary data on movement patterns of wild Mekong catfishes. The methods and lessons learned from this study can be used for future positional telemetry research to address management-relevant uncertainties about migration corridors, habitat use, efficacy of fish reserves, and river development planning.

We conducted a field experiment to test the hypothesis that intragastric radio-tagging contributed to increased prespawn mortality (PSM) of adult Chinook Salmon (Oncorhynchus tshawytscha) after collection and transport to spawning sites above high-head hydroelectric dams. We assessed PSM rates of 970 wild and hatchery Chinook Salmon collected during trap-and-haul operations that were released untagged, tagged with PIT tags only, or double-tagged with PIT tags and radio transmitters, and then recovered as carcasses in two Willamette River (Oregon) tributaries from 2009–2015. Results revealed no evidence PSM rates were higher in PIT-tagged samples compared to untagged (but not unhandled) control samples. PSM rates in double-tagged samples were variable among years and between locations and indicated that radio-tagging effects were absent or small in effect size, on average, within each population. While we did not detect a consistent negative double-tagging effect across locations and years, results suggest that the potential for radio-tagging effects should be incorporated in study planning and design. We recommend that researchers use experimental designs that include control groups for directly evaluating tagging and handling effects on study outcomes. Received 28 Jun 2017 accepted 19 Oct 2017 revised 03 Oct 2017