Study On Biology And Population Dynamics Of Schizothorax Macropogon In The Yarlung Tsangpo River

Schizothorax macropogon is one of the main economic fishes in Tibet area,only distributed in the upper and middle reaches of the Yarlung Tsangpo River and its tributaries.Under the pressure of growing demand for aquatic,S.macropogon is facing the threat of overfishing.We collected 858 samples from the Yarlung Tsangpo River monthly to study the biology characteristics and population dynamics of S.macropogon.Collections were conducted through a combination of floating gillnets;set gillnets and trap nets during 2008~2009 and in 2012.The main results were as follows:1.The study materials consisted of 229 samples.The typical annulus pattern with alternative wide zones and narrow zones was found on otolith and vertebrae.Annuli of otolith formed from March to June once a year.The maximum age observed was 14 and 13 of S.macropogon on otolith and vertebrae respectively.There was no significant difference between the results of them.The IAPE value of otolith and vertebrae is 1.43% and 4.28%,respectively.Otolith was more accurate and precise than vertebrae of S.macropogon for aging estimation.2.The standard length(SL)ranged 98.0~474.0 mm for the samples collected during 2008~2009 and 78.0~438.0mm for the samples collected in 2012,respectively.The body weight ranged from 50.1~1772.1 g for the samples captured during 2008~2009 and 7.3 ~1682.3g captured in 2012,respectively.Estimated ages ranged 2~24yr with a mean value of 10.0 ± 4.1yr for the specimens collected during 2008~2009 and 1~23yr with a mean value of 5.7 ± 3.6 yr for the specimens collected in 2012,respectively.The SL and BW are usually linked by an allometic relationship: estimated by the individuals collected during 2008~2009,were: BW=0.877×10-5SL3.104 for females,The von Bertalanffy growth equations,estimated by the individuals collected during 2008~2009,were: Lt=523.0[1-e-0.121(t+0.425)]for females and Lt=648.0[1-e-0.090(t+0.518)]for males,respe-cttively,while the vonBertalanf-fy growth equations,estimated by the individuals collected in 2012,were: Lt=445.8[1-e-0.190(t-0.5763)for females and Lt=428.5[1-e-0.218(t+0.154)]for males,respectively.3.The feeding intensity of S.macropogon was different in months,which indicated that it was high in April,October,November and December and very low from May to September.According to IRI,the main food was diatoms,macroinvertebrates,small intervebrates and organic detritus,while based on the W% and Ip%,macroinvertebrates and organic detritus was the main food,special Chironomid larvae and Hydropsychidae larvae.It was different with seasons,fish sizes and sexes for H' and J.The dietary of S.macropogon was wide and no significiant difference among seasons,fish sizes and sexes.The feeding habits fited to the comformation of predatory device of S.macropogon.4.Estimates of the total mortality rate(Z)were 0.61year-1 for females and 0.57year-1 for males.The natural mortality rates(M)were estimated as 0.15year-1 and 0.19 year-1 for females and 0.17 year-1 and 0.24 year-1 for males using two empirical methods: tmax-based estimator and growth-based method.Under the current harvesting strategy,the stock of S.macropogon may be over-exploited when the M was low,while the male population may be in full exploitation in the Yarlung Zangpo River if the M was high.Though raise the age at first capture may be effective to conserve the S.macropogon stock,it may have effects on the income of local fishermen and on the biological invasion.