Study on the eco-hydrological factors and flow regime requirement on spawning of four major Chinese carps in the middle reaches of Yangtze River

Abstract

The four famous freshwater fishes,i.e.black carp(Mylopharyngodon piceus),grass carp(Ctenopharyngodon idellus),silver carp(Hypophthalmichthys molitrix) and big head(Aristichthys mobilis) are the main fishes in Yangtze River.On the basis of four surveies on the four major Chinese carps in 1960s,1970s,1980s and 1990s,data of the spawning amount in Yidu reach and Jianli reach were available.These reaches are located below Yichan gauge station 40km and 210km respectively in the middle reaches of Yangtze River.Daily discharges from 1900 to 2004 in Yichan gauge station were adopted as references discharge for the above two studied target reaches.Three eco-hydrological factors,such as,number of discharge rise events,total days with discharge rise(DDS) and average DDS for discharge rise process during May and June were extracted and used to build a relationship with spawning amount of the four major Chinese carps during the same period.It was found,the relationship between total DDS and spawning amount is significant in Yidu reach,other relationships are slight.So,the total DDS plays an important role in spawning amount in the middle reach of Yangtze River.Analysis also tells that the total DDS during May and June does not show significant trend in the past 105 years.This implies that the spawning condition on eco-discharge for the four major Chinese carps has been relatively stable during the past 105 years.However,after the Three Gorge Project(TGP) is built,the flow regime would be altered and not suited for spawning.So,based on RVA method,total DDS of 22.1±7.2 days during May and June should be guaranteed.This should be regarded as the flow regime requirement for the regulation of TGP.