POPULATION RESOURCES AND FISHERY MANAGEMENT POLICIES OF PTYCHOBARBUS DIPOGON IN THE YARLUNG ZANGBO RIVER

Ptychobarbus dipogon is endemic to China and has been threatened by overfishing and biological invasion. To examine 956 individuals collected from Lhaze to Nyemo of Yarlung Zangbo River, the population resources and fishery management policies of this species were studied by using per-recruit models from October 2008 to September 2009, April 2012 to July 2012 and in March 2013 respectively. The total instantaneous annual mortality (Z) for female and male P. dipogon was 0.52/year and 0.70/year, respectively. The range of natural mortality (M) and current fishing mortality (F_cur) for females were 0.10—0.17/year and 0.35—0.42/year. The range of natural mortality (M) and current fishing mortality (F_cur) for males were 0.14—0.24/year and 0.46—0.56/year. The range of spawning potential ratio of P. dipogon was 3.1%—6.7% for females and 9.8%—18.2% for males, both of which were all significantly lower than the threshold reference point (25%). These results indicated that the stock of P. dipogon had been over-exploited under the current fishery management policy. To evaluate protective effect of capture age and seasonal closure, 14 different fishery management policies were simulated. The results show that raising the fishing age to not less than 15 years or setting the season closure time from February to June can effectively protect the population of the diagonal nematode.