Is there evidence that the Chinese paddlefish (Psephurus gladius) still survives in the upper Yangtze River? Concerns inferred from hydroacoustic and capture surveys, 2006–2008

Summary

Due to the rarity of Chinese paddlefish (Psephurus gladius), very little information is available on this species. In order to save this critically endangered giant species, four large-range hydroacoustic surveys (using an echo sounder with a 199 kHz, 6.8° split-beam transducer) and capture surveys (by drift nets and setlines) were conducted in the upper Yangtze River during 2006–2008. According to the target strength (TS) study on Polyodon spathula (Hale et al., 2003) and Love’s formula about TS-fish length relationships (Love, 1971), the four acoustic surveys identified nine potential targets (TS > −26.29 dB) of P. gladius, two (TS > −22.40 dB) of them very probably the fish species sought. A total of 4762 setlines, 111 anchored setlines and 950 drift net catches were conducted in which 472 large fish specimens of various species were caught. However, no single P. gladius was caught directly. The gear used did not allow quantitative capture over rough ground with deep holes, perhaps allowing some large fish to effectively hide or escape; the hydroacoustic signals indicated this as likely. In any case, it is strongly suggested that P. gladius is on the verge of extinction and further rigid measures are proposed to save the very few remaining specimens.