| The aquatic biodiversity is facing a serious crisis in the Yangtze River Basin.According to the current survey,more than 30% of the fish are on the verge of extinction.The Psephurus gladius was declared extinct in 2020.The natural reproduction of the flagship species Acipenser sinensis has been interrupted for 4consecutive years(2017—2020).In order to promote the restoration of aquatic biodiversity in the Yangtze River Basin,a 10-year fishing ban system has been implemented in key water areas such as the mainstream and important tributaries of the Yangtze River,and large river-connected lakes.The fish population has different life history characteristics,and has different responses to the fragility of fishing and the recovery rate of the population after the fishing ban in the Yangtze River.How to effectively protect the biodiversity of the Yangtze River fish after the ban has become an urgent issue.This study uses Tenualosa reevesii as the research object,and systematically studies the stock resources of Tenualosa reevesii and other fishes by combining literature data combing,field investigation and theoretical model analysis;using extinction models to perform numerical deduction on Tenualosa reevesii populations;analyzed the vulnerability index and resilience of fish populations in the Yangtze River Basin,scientifically evaluated the changes in fish populations in the Yangtze River Basin,and based on the restoration of different populations take targeted protection measures,sort out and establish evaluation indicators for the priority order of fish protection after fishing ban.The main results in the research were as follows:(1)Relying on the Yangtze River Fishery Resources and Environmental Investigation Project,from 2017 to 2020,a basin-wide fishing survey was conducted on the Yangtze River to investigate the current status of fish population resources such as Tenualosa reevesii.A total of 321 species of fish were collected in this survey,of which 15 were exotic species.At the same time,129 species of fish were not collected and 108 species were listed in the IUCN Red List.The proportion of species found in this survey is very high,and the survey work was sufficient to cover most of species present in the area.However,we did not find a single specimen of Tenualosa reevesii.(2)The extinction probability and extinction time of Tenualosa reevesii.were numerically estimated by using five complementary extinction models based on sighting records.The results of the study showed that the Tenualosa reevesii has a significant extinction probability in the Yangtze River,Pearl River and Qiantang River(P<0.05).Solow(1993)showed that the extinction time of Tenualosa reevesii in Yangtze River,Pearl River and Qiantang River was 1997,1999 and 1993 respectively,with an estimated upper bound of a 95% confidence interval for extinction time in2002,2000 and 1997 respectively.The OLE method showed that the extinction time of Tenualosa reevesii in the Yangtze River,Pearl River and Qiantang River was 2002,1997 and 1995 respectively,with an estimated upper bound of a 95% confidence interval for extinction time in 2010,2001 and 2002 respectively.Both the Solow(1993)method and the OLE method show that the extinction time of Tenualosa reevesii in the Qiantang River is the earliest and the latest in the Yangtze River.(3)The current situation of fish resources in the Yangtze River is systematically studied by combing literature and field investigation,analyzes the vulnerability index and resilience of fish in the Yangtze River,and scientifically evaluates the changes of fish population resources in the Yangtze River Basin.The result shows:(i)The proportion of fish threatened species in the Yangtze River is 25.1% lower than the global average(29%),and the proportion of Data Deficient is 18.6% higher than the global average(18.4%).(ⅱ)The species that have a maximum length longer than or equal to 100 cm most often belonged to the Acipenseridae,Polyodontidae and Anguillidae were predicted to be some of the most vulnerable Yangtze River fishes.Moreover,the largest species of grouper Acipenseridae(Acipenser sinensis),Polyodontidae(Psephurus gladius)and Anguillidae(Anguilla japonica),which are all threatened by extinction globally.(ⅲ)Species with a higher vulnerability index tend to have a larger body size,lower intrinsic growth rate,and lower resilience,while species with a lower vulnerability index have the opposite.Generally,larger body size Yangtze rivers fishes(e.g.,Psephurus gladius,Acipenser sinensis,Acipenser dabryanus,)are predicted to be more vulnerable to fishing while smaller body fishes(e.g.,Siniper caundulata,Rhinogobius cliffordpopei)are predicted to be high resilience.In summary,in order to prevent further extinction of species,in addition to observing the fishing ban,we must invest more research and resources to find out those species that are less concerned but face the greatest extinction risk and may bring greater loss of diversity.The present situation of endangered fish population resources in the basin was analyzed by numerical simulation of fish population model.It is very urgent and feasible to establish an index system for evaluating the priority protection order of fish after the fishing ban,so as to provide scientific basis for the research on the protection of fish species after the fishing ban in the Yangtze River. |
