Population Characteristics And Habitat Fish Community Structure Of Chinese Sturgeon In The Yangtze River Estuary

This study has carried out long-term tracking monitoring and scientific research on the natural population characteristics,migration habits into the sea and the relationship between the fish communities in the Yangtze River Estuary.On this basis,we will carry out research on the protection of Chinese sturgeon,such as releasing,artificial domestication,migration and distribution of marine Chinese sturgeon,protect the population of Chinese sturgeon in the Yangtze River Estuary and marine Chinese sturgeon,so as to continue the population of Chinese sturgeon.The main research contents and results are as follows:1.Artificial domestication of wild juvenile of Chinese sturgeon can achieve the purpose of individual rescue,living gene preservation and population diversity preservation.In 2006 and 2015,160 wild juvenile Chinese sturgeon which caught by mistake in the Yangtze River Estuary were studied on the biological characteristics under the artificial domestication environment.The results showed that the average body length and weight of Chinese sturgeon increased from 15.4±0.64cm and 26±1.34g to 29.2±0.75cm and 108±3.87g from June to August in 2006,with an average daily growth of 1.54mm and an average daily gain of 0.9g.In 2015,after three months of artificial domestication,the average body length and weight of Chinese sturgeon increased from 14.90±0.22cm and 22.25±1.34g to 28.32±0.84cm and 148.65±3.02g,with an average daily increase of 1.49mm and 1.40g.The fitting relationship between body length and body weight of juvenile Chinese sturgeon was W₂₀₀₆=0.1215L^2.0313?R²=0.9457??W₂₀₁₅=0.0086L^2.9051?R2=0.996?.The growth of juvenile Chinese sturgeon in 2015 was better than that in 2006.When the water temperature was over 24?,the instantaneous growth?weight?rate of juvenile Chinese sturgeon decreased with the increase of water temperature.The variation coefficient of body length and body weight of the wild juvenile Chinese sturgeon domesticated artificially is small,which is lower than 2.60%and 3.66%on average.Indicating that the individual growth speed is fast,the difference is small,and the size and specification are neat,which also shows that the growth of the wild juvenile Chinese sturgeon domesticated artificially is not stagnant or slow due to the change of environment and food.Compared with the juvenile of Chinese sturgeon in the same period of wild environment,the growth of the two species is different.On the whole,the growth of wild juvenile Chinese sturgeon in the artificial domestication environment is better than that in the natural environment.In addition,the death rate of Chinese sturgeon was5.0%.The fatal diseases included enteritis,Saprolegniasis and gill-rot disease.The results showed that the juvenile of wild Chinese sturgeon had strong adaptability to the artificial domestication environment,fast growth speed and easy domestication,which indicated that the domestication of the juvenile of wild Chinese sturgeon was helpful to the protection of Chinese sturgeon.2.In 2004-2018,6600 juvenile Chinese sturgeon,10 adult Chinese sturgeon?age>8 years old?and 74 adult Chinese sturgeon?age 2-8 years old?were detected in the Yangtze River Estuary by sampling fixed monitoring network and random investigation throughout the year.The monitoring results show that:From 2004 to 2018,the replenishment of juvenile Chinese sturgeon in the Yangtze River Estuary decreased continuously,and after 2014,the replenishment was broken.In 2014,2016 and 2018,no juvenile Chinese sturgeon was detected,which further confirmed the change of natural reproduction behavior of Chinese sturgeon from continuous to occasional.In 2015-2018,the temporal and spatial distribution characteristics of juvenile Chinese sturgeon in the Yangtze River Estuary changed with the literature records.The time of first emergence?nearly one month?,the time of last withdrawal?about one month?and the time of emergence changed from May to September every year to the new characteristics of April to October in discontinuous years.It is inferred that a new spawning ground may be formed in the Yangtze River and it is far away from the Yangtze River Estuary Closer,or the natural spawning time of Chinese sturgeon is earlier.The average body length and body weight of juvenile Chinese sturgeon in the Yangtze River Estuary are 22.7cm and99.0g,both of which are decreasing year by year.There was a significant relationship between growth index b and the change of plumpness of juvenile Chinese sturgeon in the Yangtze River Estuary.According to the damage of nets to juvenile Chinese sturgeon,the death rates of nets from high to low were fixed net?24.84%?,gill net?18.45%?,floating net?9.33%?and inserted net?3.05%?.Based on the study on the changes of the supplement amount,temporal and spatial distribution and growth characteristics of juvenile Chinese sturgeon in the Yangtze River Estuary,the direction of protection and management of Chinese sturgeon in the Yangtze River Estuary and the Yangtze River Basin is provided.3.From 2004 to 2014,12570 Chinese sturgeons were released in the Yangtze River estuary waters to study the migration habits and marine distribution of Chinese sturgeon,in order to improve the protection capacity of marine Chinese sturgeon population.872 wild Chinese sturgeons and 11698 artificial breeding Chinese sturgeons?F₁?were released,and the age included 11 ages from 1 to 25.In vitro and in vivo double markers were used in the release of Chinese sturgeon,including 5 kinds of general tags:Passive Integrated Transponder tags?PIT?,Silver brand tag?SBT?,Plastic streamer tag?PST?,Plastic bone armor tag?PBT?,Plastic tipped dart tag?PDT?,and 1kind of satellite tag:POP-UP satellite archival tag?PAT?.In the process of transportation,the released Chinese sturgeon is packed and transported with oxygen filled monomer.In the process of releasing,the Chinese sturgeon is put into a continuous live water chute and slide to reduce the damage of the Chinese sturgeon.The results show that:?1?In total,24 general tag of Chinese sturgeon were recapture and 18PATs signs of Chinese sturgeon were collected.The recovery rate of general tag is0.19%,and the recovery rate of PAT is 52.9%.?2?The recovery time of tag or tag information is in the range of 1-198d,which shows a trend of high recovery rate in the early stage of releasing and decreasing with the increase of releasing time.The results show that the Chinese sturgeon can survive for at least half a year in the field,and the early catch after releasing is one of the main factors for the loss of releasing Chinese sturgeon.Setting the falling off time is inversely proportional to the number and recovery rate of PAT recovery.Setting the fall off time is inversely proportional to the amount of PAT recovered.The short-term effect of pat is higher than the long-term effect.?3?The release of old Chinese sturgeon is a sign of high recapture rate.The highest recapture rate was 50.00%in the 12th and 16th instars,followed by 25.00%in the 11th instar,and 16.00%in the 9th instar.The recapture rate of other age groups was lower than 10%.The lowest recapture rate was 0.11%for the first age Chinese sturgeon.?4?Among the recapture Chinese sturgeons,PAT indicates that all the Chinese sturgeons enter the sea,and 50.00%of the general tagging Chinese sturgeons enter the sea.?5?The North channel of South Branch in the Yangtze River Estuary is the main place for Chinese sturgeon to stay and the main channel for Chinese sturgeon to enter the sea.?6?The Chinese sturgeon can adapt to the saltwater environment in a short time??5d?,and migrate to the sea from the Yangtze River Estuary in the fresh water environment in 7d.There are 18 Chinese sturgeons caught back in the East China Sea and 12 in the Yellow Sea.The migration direction into the sea is uncertain.They are randomly distributed in the Yellow Sea and the East China Sea,and can return and migrate between the East China Sea and the Yellow Sea.?7?The Chinese sturgeon released from the Yangtze River estuary is distributed in the waters of the Yangtze River Estuary and the coastal continental shelf of the East China Sea and the Yellow Sea.The longitude span is 7°and the latitude span is 9°.It indicates that the Chinese sturgeon reaches the west coast of the Korean Peninsula as far as North,with a straight migration distance of 697km.The sea area of five islands in Nagasaki county,Japan is the farthest in the East,with a straight-line migration distance of 630km.It reaches Ningde sea area of Fujian Province in the south,with a straight migration distance of 640km.?8?The Yangtze River Estuary and Zhoushan Archipelago sea area are the main distribution areas of Chinese sturgeon.?9?The average straight-line speed of the Chinese sturgeon with PAT and general tags is 7.89km/d and 6.21km/d.There is no significant correlation between migration speed and migration distance.?10?The artificial breeding of Chinese sturgeon in the Yangtze River Estuary still has the habit of wild Chinese sturgeon.After releasing,it can survive for at least 6 months,adapt to salinity quickly and enter the ocean,and can eat and grow normally.The results show that the Chinese sturgeon can adapt to the marine environment and survive and grow in the sea.Therefore,the proliferation and release of Chinese sturgeon in the Yangtze River Estuary has a certain contribution to the artificial increase of Chinese sturgeon population resources.4.We investigated the co-occurrence mechanisms of how species of fish assemblages coexist within the Yangtze River estuary,based on pair-wise probabilistic analyses,networks and theory.And evaluating its fish community can provide the restoration and management of ecosystem with scientific basis.Generalized additive model?GAM?and boosted regression tree?BRT?were built to establish the relationship of fish community diversity index and environmental and spatio-temporal variables based on data collected in the Yangtze River Estuary during 2012-2014.The results obtained show that:?1?In this estuary the species of the fish community were mainly randomly associated,which suggesting a considerable neutral element in the assembly of local fish communities in the Yangtze River Estuary.Environmental filtration mechanism may have greater impact on fish species assemblages rather than species interaction.A significant seasonal difference in spatial co-occurrence patterns of fish species is mainly related to seasonal replacements in marine migratory fish and estuarine settled fish species.The seasonal replacements of fish species with high weighted degree and between ness centrality may also have caused the high number of randomly associated pairs of species.The results also show that Collikithys lucidus has a strong ability to control information exchange within the community and is at the core of the fish community structure in the Yangtze River Estuary.Results presented in this study will be useful for developing local fish biodiversity management and conservation strategies.?2?Salinity,p H and Chlorophyll-awere variables which have the most contribution on diversity index,and p H,dissolved oxygen and Chlorophyll-awere the most contributive variables on richness index.BRT models showed better goodness of fit and lower prediction error than GAM models.In contrast to GAM models,BRT models could carefully distinguish the fish community index in each station areawith respect to the spatial prediction.The diversity index in external wateris obviously greater than which in internal water,meanwhile,the station which has higher latitude also has a higher diversity index no matter in external water or internal water.