Study On Population Biology And Fishery Management Strategies Of Protosalanx Chinensis In Dalong Lake

Dalong Lake,located in Daqing,Heilongjiang Province,at the lower reaches of Nenjiang River,is the core production area of Protosalanx chinensis in "the first county of Protosalanx chinensis in China"--Durbert Mongolian Autonomous County.The development of Protosalanx chinensis multiplication industry in Dalong Lake has brought considerable economic and social benefits to the local area.However,in recent years,the yield per unit area of Protosalanx chinensis in Dalong Lake is relatively low,and the monitoring and research on the population dynamics of Protosalanx chinensis is still lack of systematic,which is not enough to guide its fishery management.Therefore,this study carried out a month-by-month continuous follow-up survey on the population of Protosalanx chinensis in Dalong Lake from April 2021 to December 2021,taking the growth,feeding,breeding and population resource status evaluation of Protosalanx chinensis population as the research content,aiming to provide basic scientific data for the regulation of Protosalanx chinensis breeding population and the establishment of sustainable high-yield technology.The main research methods and results are as follows:From April to December,940 samples were collected monthly to explore the growth characteristics of Protosalanx chinensis.Its body length ranges from 10mm to 178mm,with an average of 104mm;The body weight range is 0.1～27.2g,with an average of 7.42g.The relationship between body length and body weight was Wt=3 × 10-6 Lt 3.0886(R2=0.900)(Lt,Wt are the body length and body weight of Protosalanx chinensis at age t respectively),which were consistent with allometric growth characteristics.Using the VBGF growth equation to fit Protosalanx chinensis samples,the body length growth equation of Protosalanx chinensis in Dalong Lake was Lt=183.75[1-e-2.1(t+0.074)],and the body weight growth equation was Wt=29.54[1-e-2.1(t+0.074)]3.0886.The body length growth acceleration equation was dLt/dt=384.825e-2.1(t+0.074),and the body weight growth acceleration equation was dWt/dt=191.598e-2.1(t+0.074)[1-e-2.l(t+0.074)]2.0886.The growth characteristic index of Protosalanx chinensis in Dalong Lake was 4.85,and the theoretical initial age was-0.074a.The inflection age was 0.463a,the corresponding theoretical body length was 124.26mm,and the theoretical body weight was 8.82g;the critical age is 0.83a,the corresponding theoretical body length was 156.01 mm,and the theoretical body weight was 17.82 g.The growth rate of Protosalanx chinensis in Dalong Lake was relatively fast from May to September,especially there was a rapid growth stage between May and June.In spring(April to June),four samples were collected from Protosalanx chinensis in Dalong Lake during the feeding stage of Protosalanx chinensis zooplankton,and the contents of the stomach were identified,measured and counted.It was found that Protosalanx chinensis mainly feeds on large zooplankton(Cladocera and Copepods)in spring,and also feeds on a small number of nauplii.During this period,the food selectivity of Protosalanx chinensis also changed significantly with individual growth:only copepods and a small number of nauplii were fed in April;In May,both cladocera and copepods ate,and cladocera was slightly more than copepods;eat a small number of copepods in early June;in late June,only cladocera was eaten,showing a shift from preference for copepods to preference for cladocera.Protosalanx chinensis has certain selectivity to the type of zooplankton.Protosalanx chinensis prefers to eat copepods in April and May,and cladocera in June.At the same time,Protosalanx chinensis is also selective for the size of zooplankton.From April to early June,with the growth of the body length of Protosalanx chinensis,the body length of zooplankton that prefer to eat also increases correspondingly,and the body size of zooplankton that prefer to eat decreases in late June.The average individual absolute fecundity(FA)of Protosalanx chinensis in Dalong Lake was 9518.43 ± 4897.49 eggs,the average body length relative fecundity(FL)was 66.82 ± 29.36 eggs/mm,and the average body weight relative fecundity(Fw)was 764.85± 206.09 eggs/g.The body size of Protosalanx chinensis breeding population in Dalong Lake was mostly distributed between 120 and 150 mm,accounting for 87.72%of the total,and its breeding contribution rate was 82.72%,which was the main breeding contribution group;The reproduction contribution rate of 150～180mm body length was 17.28%.FA and FL were significantly correlated with body length(L),body weight(W),ovarian weight(WO),net body weight(WN),fullness(K)and gonadosomatic index(GSI),respectively.Fw was significantly correlated with K,WO and GSI,respectively,and both had the highest correlation with ovarian weight;Fw was significantly correlated with K,WO and GSI,and the highest correlation was found with GSI.The optimal fitting equations between individual fertility and various biological indicators were mostly quadratic functions,and a few are logarithmic functions.According to the multiple stepwise regression analysis,the best fitting equation was:FA=2366.776+2668.689*WO-60.08 WN(R2=0.846);FL=18.476+13.292*WO(R2=0.768);Fw=467.27+7.001*GSI(R2=0.343).The ovarian weight and net body weight can be used in the actual production to estimate the individual absolute fecundity of Protosalanx chinensis in Dalong Lake.The body length distribution frequency of Protosalanx chinensis in each month was calculated,and then the total mortality coefficient of Protosalanx chinensis population in Dalong Lake was 4.21/a according to the transformation catch curve fitted by FIS AT II software.According to Pauly’s empirical formula,the natural mortality coefficient was 1.12/a,and the fishing mortality coefficient was 3.09/a.According to the mortality coefficient of Protosalanx chinensis population,the population exploitation rate was 73.4%,and the annual survival rate was 1.48%.According to various fishery indicators,the Beverton-Holt dynamic comprehensive model was used to analyze and judge that the current Protosalanx chinensis population in Dalong Lake was in the state of overexploitation.Considering the individual growth potential,population instantaneous biomass and population supplement,it was recommended to increase the opening body length to 115.40 mm and postpone the start of fishing to late August.