| The Chinese white dolphins(CWDs),a kind of marine mammal,is widely distributed along the coasts of the East Indian Ocean and the West Pacific Ocean.Compared with offshore cetaceans,CWDs are more susceptible to human disturbance because of their coastal habitats.Xiamen Bay is a relatively well-protected ecological environment in developed regions,but human activities still seriously threaten the local dolphin population.In recent years,there have been numerous sea-related construction projects in Xiamen Bay.Assessing the impact of these projects on the local dolphin population and formulating relevant conservation policies require the support of population data.However,previous population ecological studies have indicated that the CWDs in Xiamen Bay have a constantly variational population status.Therefore,it is necessary to conduct a real-time comprehensive population ecological monitoring to assess the situation of CWDs in Xiamen Bay accurately.In this study,an updated individual identification database of CWDs in Xiamen Bay was constructed through field surveys.Based on this,an immediate population ecological assessment of the population size,survival rates,social structure and habitat utilization of CWDs in Xiamen Bay was carried out.Also,corresponding conservation suggestions were put forward.This research provides an essential reference basis for relevant environmental impact assessment and the CWDs conservation.This study's main contents and results are as follows:(1)The research team used Discovery software to establish a database of individual identification of CWDs in Xiamen Bay based on field survey data collected from 2018 to 2019.49 individuals were recorded in this database,including 31 adults,13 juveniles/sub-adults,and 5calves.(2)Based on the database,the MARK software was used to estimate the population parameters under the optimal model.The results obtained are that the apparent survival rate of adults,non-calf individuals,and juveniles/sub-adults are 0.980± SE 0.02,0.878 ± SE 0.02,0.700 ± SE 0.05,respectively,and the total population size is 54(43-67).(3)Based on the database,the SOCPROG software was used to analyze the social structure.The cluster analysis is divided into two clusters when modularity reached the maximum,which indicated this population could be divided into two communities with very low association.There were 21 pairs of individuals whose association index exceeds 0.7 within the population.The average group size of the population is 5.75,and the most common group size is 3.There are obvious differences in the group size and schooling propensity of the two communities.(4)Based on the database,Arc GIS software and R language were used to analyze home ranges.According to the estimation of the minimum convex polygon and kernel density estimation,the historical and current distribution,seasonal distribution,community distribution and fostering areas are obtained.The study indicated that the adult individuals of the CWDs in Xiamen Bay have been at a stable and high survival rate level in the recent ten some years.However,the apparent survival rate of young dolphins has dropped sharply and is at a low level.At present,the population size of CWDs in Xiamen bay is continuing to decline and has reached the lowest point in the history of research.The CWDs population in Xiamen Bay is still composed of two communities with a very low association,the eastern community and the western community,whose core habitats are completely independent.The eastern community mainly uses the eastern area of Xiamen Bay,while the western community uses the western area of Xiamen Bay.Compared with 5years ago,some specific individuals are more closely related.This phenomenon mainly exists between one juvenile and multiple adults which may be a cooperative parenting strategy adopted by dolphins to cope with the lower survival rate of nonages.The group size in different communities is polarized.Individuals in the eastern communities tend to cluster.In contrast,western individuals usually form a smaller group.The variation of schooling propensity may be an adaptation strategy of different habitat environments and population size reduction.The populations are mainly distributed in the waters near West Harbour-Jiulong River Estuary,Tongan Bay Estuary,and Dadeng Island.Their core habitats and fostering areas have been shrunken and gradually migrated away from the artificial shoreline.The seasonal distribution of the population is significantly different.The distribution range of the wet season expands towards offshore,which may be the response of the dolphins to changes in food resources.In general,the population of CWDs in Xiamen Bay continues to decline due to the low survival rate of young individuals.The division of social structure is gradually deepening,and the habitat is shrinking and migrating.The population reaches the critically endangered status by criteria of the IUCN Red List of Species.Sea-related projects and aquacultural activities around the fostering areas and inbreeding may be the main reasons for this situation.Given the status quo of the Chinese white dolphin population in Xiamen Bay,this study puts forward corresponding conservation suggestions:(1)optimize and adjust nature reserves,(2)strengthen law enforcement,(3)repair damaged habitats,(4)build ecological corridors,(5)explore ex-situ conservation. |
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