Study on Fishery Ecological Environment and Fish Species Diversity in Yantan Water Area

Yaoquan HAN，Anyou HE，Li HUANG，Jun SH I，Dapeng WANG，W eijun WU

1.Guangxi Key Laboratory of Aquatic Genetic Breeding and Healthy Aquaculture，Guangxi Academy of Fishery Sciences，Nanning530021，China；2.Guangxi International Business Vocational College，Nanning 530007，China

1 Introduction

The fishery ecological environment is foundation for survival，growth and breeding of fish resources，the quality and change of fishery ecological environment will exert a series of short-term or long-term director indirect influence on fish resources.High quality fishery ecological environment needsmutual support of excellent aquatic ecological and natural environment and reasonable composition of aquatic organism community［1］.Hongshui River where the Yantan water area is situated is themost important fishery water area in upstream of Xijiang River，is the key enhancement and release area specified in Overall Plan for Enhancement and Release of National Aquatic Organisms［2］，and there is the most complex aquatic ecological environment and the largest fish spawning ground of Xijiang River basin［3］.Yantan Reservoir is the second largest reservoir inmain stream of Hongshui River.It consists of 166 km original river section and 107.5 km2surface water area，it controls water area of 107000 km2.Because water conservancy dam construction and fishery development are not scientific，there has been huge change in ecological environment of Hongshui River basin，such as occurrence of serious deterioration of fishery ecological environment，death of numerous fishes，and excessivemussels.Evaluating current situation of fishery ecological environment in the reservoir area and scientifically restoring ecological environment in water area aremajor projects of production and ecological safety.In recent30 years，many scholars have made extensive researcheson cross sections of HongshuiRiver basin and Yantan water area and have obtainedmass data，but there is no research about evaluation of fish species diversity in reservoir area，especially after the artificial enhancement and release.In 2003，freshwatermussel problem appeared in Yantan water area.After 2006，freshwatermussel started propagating rapidly，fishery production in the reservoir area suffered a huge loss and hidden danger of ecological safety appeared.From 2009，reservoir area started restoration of fishery ecological environment including enhancing and releasing black carps.This study is the first survey of fishery ecological environment in reservoir area in recent years.It is expected to provide reference for fishery organizations formulating development plan of enhancement and release of fishes.

2 Materials and methods

2.1 Distribution of sampling points and frequency of samp lingWe carried out a survey in 4 cross sections（as shown in Fig.1），collected water sample，specimens and data of aquatic organism including phytoplankton，zooplankter，zoobenthos，and fishes.Besides，we collected samples of planktonic organisms in Cifu Bridge cross section in Bama County of Guangxi.We sampled one time separately in March，June，September and December in 2013.

2.2 Sampling and analysis of water qualityWater samples were collected simultaneously in 5 cross sections in accordance with HJ 495-2009Water quality-Technical Regulation on the Design of Sampling Programs and HJ493-2009Water Quality-Technical Regulation of the Preservation and Handling of Samples.Water quality was tested usingmethods specified in GB 3838-2002 Environmental Quality Standards for SurfaceWater and GB 11607-1989Water Quality Standard for Fisheries.Wemeasured total phosphorus，total nitrogen，volatile phenols，non-ionic ammonia，oils，mercury，copper，zinc，lead，cadmium，pH value of the index，and measured air temperature，water temperature，clarity，turbidity and dissolved oxygen and other indicators.

2.3 Survey and analysis of planktonic organismsSurvey and analysis of planktonic organisms were carried out with reference to CAF2005 0001 Regulations on Survey of Fishery Natural Resources in Inland Water Area（for Trial Implementation）.Trophic level and water qualitywere evaluated in accordancewith SL218-98 Standard for the Fishery Trophic Classification of Reservoirs with average quantity per unit of planktonic organisms as basis.

2.4 Survey and analysis of the catchesWe selected specialized fishermen normally operating in fixed areas of upstream，midstream and downstream，and made a record of their daily catches and biological data ofmajor fishes.The operation areas aremainly near Tian'e County，Anlou Bridge of Donglan County，and front area of Yantan Reservoir dam in Dahua County.Fishermen conduct normal production in accordance with usual fishing gear and methods，such as fishing nets，fishhooks，and fishing cages.Most fishermen place fishing netsat18：30 to3：00 in the nextday，and haul up fishing nets at 7：00.Net is 400-500 m long，and the mesh is4-10 cm.There are 4-6 fishing cages and 300-400 fishhooks.

Analysismethods of the catches include statistical method，Shannon-Weiner diversity index［4］，Wilhm improvement index［5］，and DG-Fspecies diversity index［6］analysismethod［7］.

Calculationmethods of Shannon-Weiner index（H）and Wilhm improvement index（H＂）.

where Pidenotes the proportion of the i-th organism individual to total organisms，S refers to total organism types，N is total organisms，and Wisignifies the proportion of the i-th organism quality to total organism quality.

The calculationmethod of DG-Fspecies diversity index is as follows：

where Skidenotes total organisms of genus i of family k，Sksignifies total organism individuals of family k，n is the number of genus in family k，m refers to total of the whole organism families，Sjsignifies total organisms of genus j，S is total organisms，and p is total organism genus.

3 Results and analyses

3.1 W ater qualityWater quality test results indicate that total phosphorus，volatile phenols，non-ionic ammonia，oil，mercury，copper，zinc，lead，cadmium，pH value of water in Yantan Reservoir conform to category III standard specified in Standard for Environmental Quality of SurfaceWater（GB 3838-2002）and Water Quality Standard for Fisheries（GB 11607-1989）.Total nitrogen ofwater in Yantan Reservoir is up to 1.25-2.70mg／L，the average value is1.75mg／L.According to category IIIstandard specified in Standard for EnvironmentalQuality of SurfaceWater（GB 3838-2002），the total nitrogen exceeds 0.25-1.7 times，and the average value exceeds 74.6%of the standard of Category IIIwater，as listed in Table 1.

3.2 Planktonic organismsWe collected 6 phyla and 57 genera planktonic organisms，including 9 genera of Cyanophyta，23 genera of Chlorophyta，17 genera of Bacillariophyta，2 genera of Euglenophyta，4 genera of Pyrrophyta，and 2 generaof Chrysophyta.Bacillariophyta，Pyrrophyta，Chlorophyta，and Cyanophyta are dominant species，and the Bacillariophyta has the largestbiomass，as listed in Table 2.The average quantity per unit of phytoplankton is1.0134million ind.／L，and the average quantity per unit of organisms is1.1151mg／L.According to SL218-98 Standard for the Fishery Trophic Classification of Reservoirs，taking average quantity per unit of planktonic organisms as basis，Tantan Reservoir belongs to trophic water and the water quality is general.

Table1 Testresultsofwaterquality

Table2 Listofphytoplanktoncollected

continued

Table3 Listofzooplanktoncollected

We collected 4 types，19 families，35 genera and 43 species of zooplankton，including 4 families，8 genera and 13 species of protozoon，5 families，10 genera and 12 speciesof rotifera，6 families，7 genera and 8 speciesof cladoceia，and 4 families，10 genera and 10 species of copepoda，as listed in Table 3.There is a great difference in quantity of types of zooplankton：the sequence is Rotifera，protozoon，cladoceia and copepoda.The average quantity per unit of zooplankton is459.6 ind.／L，and the average quantity per unit of organisms is 0.6422 mg／L.According to SL218-98 Standard for the Fishery Trophic Classification of Reservoirs，taking average quantity per unit of zooplankton as basis，Tantan Reservoir belongs to oligotrophic water and thewater quality is excellent.

3.3 The catchesThe catches were surveyed in June-November 2013.Daily catcheswere recorded for single ship operation of upstream，midstream and downstream.In total，1410.2 kg and 52365 pieces of catcheswere recorded.Through search，thewhole fishes belong to 3 orders and 6 families（cyprinidae includes 6 subfamilies），17 genera and 17 species，as shown in Table4.For upstream fishermen，wemade a record of181 operating days（178 days had catches），178 pieces of catch data，the total 51351 pieces of catchesweighed 905.9 kg；formidstream fishermen，we made a record of 174 operating days（64 days had catches），64 pieces of catch data，the total430 pieces of catchesweighed 268.2 kg；for downstream fishermen，wemade a record of150 operating days（86 days had catches），86 pieces of catch data，the total 584 pieces of catches weighed 236.1 kg.Daily catches per ship for all three areas of fishermen were 2.7 kg.

According to types，quantity，and quality distribution of catches obtained，the Shannon-Weiner diversity index is0.162，Wilhm improvement index is1.814，and DG-Fspecies diversity index is 0.083.

Table 4 Data of the catches

4 Conclusions and discussions

4.1 Discussions

4.1.1Naturalenvironment forwater quality of Yantanwater area is basically normal.Testing results of water quality of Yantan water area in 1981-1982，1996-1997，2003-2004，2005-2006，and 2013 indicate that there are changes of physical and chemical indicators ofwater quality.However，except total nitrogen exceeding the standard，all other indicators conform to category IIIstandard specified in Standard for Environmental Quality of SurfaceWater（GB 3838-2002）and Water Quality Standard for Fisheries（GB 11607-1989）.

From Table 5，it can be known that the quantity of types of phytoplankton in Yantan Reservoir area is lower than historical data，the unit average quantity and biomass are slightly higher than the period before construction of the reservoir，but there is obvious decline compared with the quantity of 5 and 10 years after water storage of the reservoir；the quantity of types of zooplankton is slightly lower than the historical data，and there isobvious decline in unitaverage quantity and biomass compared with the quantity of 5 and 10 years afterwater storage of the reservoir［8］.According to unit biomass indicator surveyed，water quality of Yantan area is oligotrophic andmesotrophic，and natural environment in reservoir water area is basically normal.

Table 5 Planktonic organisms in Yantan Reservoir area in different periods

4.1.2Fish resources in Yantan water area are exhausted.According to survey results in recent 30 years for fishery ecology in Hongshui River and Yantan Reservoir area，fish types were 15 families and 70 species in 1981-1984［3］，15 familiesand 43 species in 1997-1998，and 14 families and 42 species in 2003-2005［10］，and there are 30 types of commercial fishes.Due to influence of fishing tools and methods，survey results are not fully reflecting current situations of fish resources in the reservoir area.Our survey lasts half year，but the catcheswe recorded only 3 orders，6 families，17 genera and 17 species，and the daily catches per ship is only 2.7 kg，showing gradually exhausting fish resources in the reservoir area.

4.1.3Diversity of fish species in Yantan water area is low.Shannon-Weiner diversity index reflects abundance of community species from quantity distribution of different species；Wilhm improvement index combines influence of species abundance and evenness and reflects complexness of community structure from quality distribution of different species［11］；DG-Fspecies diversity index reflects species diversity level from distribution of community organisms in familiesand genera［6］.In the second half of2013，Shannon-Weiner diversity index of the catches in Yantan water area was0.162，Wilhm improvement index is1.814，and DG-Fspecies diversity index is 0.083.Zhou Jie et al［7］，Han Yao［8］，Li Jie etal［12］，Ling Qufeietal［13］，Zhang Jiaboetal［14］，and Zhang Minying et al［15-16］made survey and diversity analysis of fish resources respectively in inland water area ofGuangxi，Lijiang River and Qian River water area，Xijiang River in Zhaoqing City of Guangdong Province，Swan Island Ancient Course of Yangtze River，Laojianghe River，and Yangtze River.Compared with Pearl River，Yangtze River valley，the fish species diversity of Yantan water area is lower，Shannon-Weiner diversity index is only 4.14%of average value of other water areas，Wilhm improvement index is59.05%of the average value of other water areas，and DG-Findex is only 15.82%of the average value of otherwater areas，as listed in Table 6.

4.1.4Fish resource structure of Yantan water area is abnormal.According to the quantity of the catches，more than 98%are small fishes（Discogobio tetrabarbatus accounts for 97.51%）.More than 50%catches are small fishes and commercial fishes account for a small portion.Except small fishes，only carps and tilapias exceed 10%，other fishes not artificially enhanced and released only account for about6%.These differ greatlywith historical data that13major commercial fishes in riversofGuangxiaccount for more than 54%［2］.Thus，it can be known that fish resources of Yantan Reservoir are exhausted，and structure of fish resources are extremely abnormal.

Table 6 Comparison in diversity of fish species in water areas

4.2 ConclusionsThis study indicates that water quality of Yantan water area is basically normal，but fish resources are exhausted，and fish species diversity is extremely low.Compared with natural rivers before construction of the reservoir，the structure of fish resources in the reservoir area is extremely abnormal.Due to barrier ofwater conservancy dam of Hongshui River，ecological environmentof Yantanwaterarea isdeteriorated.Especially，major commercial fishes such as Mylopharyngodon piceus，Ctenopharyngodon idellus，Hypophthalmichthysmolitrix，and Aristichthys nobilis lose their natural environment for reproduction and accordingly fish resources are gradually exhausted.In addition to superposition influence of other factors such as disorderly developmentof fishery and increase ofenvironmental pressure，aquatic organisms of reservoir area in recent years lose balance in structure，especially the structure of fish resources.Unreasonable fish structure will deteriorate unreasonable structure of aquatic organisms in reservoir area and increase hidden dangers of ecological safety accidents in reservoir area.According to survey results of Survey Report of Hazards of Freshwater Mussel in Yantan Reservoir Area in Dahua County，breakout of freshwatermussel in Yantan reservoir is partly resulted from sharp decrease of Mylopharyngodon piceus which is the natural enemy of freshwatermussel.

In the context of ecological safety of water area in the reservoir，it is urgent to restore ecology of Yantan water area.From the perspective of biomanipulation，fish enhancement and release carried out by fishery department should be based on thorough survey.It is recommended to increase indigenous fishes of Hongshui River and gradually restore fish structure and the diversity.For example，it is recommended to release some bottom fishes to improve bottom feeder of the reservoir area，release Mylopharyngodon piceus to eat benthic animals，and release certain quantity of carnivorous fishes to eliminate excessive small fishes and improve aquatic ecological environment and biological structure of the water area.Through correct estimation of primary productivity and fishing ground capacity，it is recommended to release Ctenopharyngodon idellus，Hypophthalmichthys molitrix，and Aristichthys nobilis to slow down and adjust eutrophication of reservoir area，reduce nitrogen and phosphorus content in water，and improvewater quality.

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