Search for Chinese paddlefish (Psephurus gladius) in the upper Yangtze River during 2009-2013 including reevaluation of data from 2006 to 2008.

Since two large specimens of Chinese paddlefish Psephurus gladius were found unexpectedly in December 2002 and January 2003, a series of measures have been undertaken to attempt to save this critical endangered species. As a part of the rescue plan, a total of eight hydroacoustic and capture surveys were conducted in the upper Yangtze River between 2006 and 2013. Preliminary results from the first four surveys (2006-2008) were reported in 2009. The later four surveys were conducted in the same area and consisted of 578 setlines, 8 anchored setlines and 2003 drift net catches. A total of 1982 fish belonging to 38 species were captured. For the hydroacoustic surveys, a BioSonics echo sounder with a vertically down looking 199 kHz split-beam transducer was applied, both for data recording, and for guiding the capture trials by drift nets and setlines. Post processing applying automatic tracking identified 7217 single targets from the eight acoustic surveys. Body size was estimated from TS values of single targets. No P. gladius were captured. The acoustic data, however, revealed at least a few observations that are difficult to interpret as something other than large P. gladius. Although not conclusive, this gives hope that this species may still exist in the river. [ABSTRACT FROM AUTHOR]