Peter J. Graf

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.

The fall Chinook Salmon (Oncorhynchus tshawytscha) population that spawns in the Hanford Reach of the Columbia River, USA is paradoxical because it is located above 4 and below 10 main stem Columbia River dams and yet is one of the largest and most productive C. salmon populations in the Pacific Northwest. A synthesis of information collected in the Hanford Reach reveals that the hydrosystem above the Hanford Reach and the management of river flows may have contributed to the recent size and productivity of this salmon population. Mechanisms for high survival and capacity at each freshwater life stage have been identified. Plausible mechanisms for contributing to high spawning capacity include: (a) more spawning habitat available during the spawning period. Plausible mechanisms for high egg‐to‐presmolt survival include: (a) reduced desiccation of redds, (b) reduced scour of redds, (c) reduced sedimentation in redds, (d) improved flow exchange within redds, and (e) increased food availability. Smolt survival may also be enhanced through the large size they attain in the Hanford Reach. This synthesis of information provides an uncommon assessment of some the positive effects of flow management from hydropower dams on a valued native fish that has occurred over the last three decades. WIREs Water 2018, 5:e1275. doi: 10.1002/wat2.1275This article is categorized under: Water and Life > Stresses and Pressures on Ecosystems Water and Life > Conservation, Management, and Awareness