Research On The Social Network Structure Of Chinese White Dolphins In Xiamen And Beibu Gulf

Cetacean lives in complex oceanic environment,showing highly dynamic social behavior strategies.For these social species,studying the social network structure,and interaction among different communities or individuals,assessing the potential impact of human activities,will contribute to the evaluation of population health and to take effective management measures.Indo-Pacific humpback dolphin(Sousa chinensis)is distributed in the nearest shore in China,which is suffering from anthropogenic activities.Since 2000,our team has conducted a series of surveys on Xiamen and Beibu populations of Indo-Pacific humpback dolphins.We have known their population size and spatial distribution pattern.However,it is unclear about the social structure,what is the relationship among individuals?Has it formed a unique network structure?Do anthropogenic activities impact the social network?In view of these,we select Indo-Pacific humpback dolphin populations at Xiamen and Beibu Gulf as research objects;based on boat-based field survey,individuals were distinguished using photographic identification technology;the association index was calculated by program SCOPROG,and the social network of Indo-Pacific humpback dolphins were constructed.Additionally,the network metrics and temporal association pattern were evaluated;the driver function of typical internal factor(calf absence and presence)and external factor(anthropogenic activities intensity)were tested.Finally,some suggestion on population protection and measure of management were put forward.The results showed:(1)The social network of Xiamen Indo-Pacific humpback dolphin.The Half-Weight Association Index,No-0 Association Indices and Lagged Association Rates supported that association between Xiamen dolphins is non-random.The temporal pattern of two levels of casual acquaintances was measured.The Xiamen population was clearly divided into three communities,namely,the Northeastern Community(21 dolphins),the Western Community(23 dolphins),and Third Community(3 dolphins).The mean association index of Northeastern Community is 0.32(SD=0.15),which was significantly higher than that of the whole population(0.13 ± 0.06)and Western Community(0.18 ± 0.09).The temporal pattern of Northeastern Community is Constant Companions,in contrast with Casual Acquaintances in the western community.(2)The social network of Beibu Indo-Pacific humpback dolphin.In Beibu Gulf,two groups were distributed respectively in Dafengjing-Nanliujiang River Estuary(DRE)and Shatain-Caotan(SC)areas,no same identified individuals were found in both area.The association pattern of individuals in both groups is all non-random.The optimal mode of DER group is "Casual Acquaintances",and "Casual Acquaintances"+ "Constant Companions" of SC group.The SC dolphins associated closely(0.16±0.06),which is similar with Xiamen population.Perhaps,the close individual association is conducive to the survival of small population.Accordingly,the association of DRE dolphins is weak(0.07 ± 0.03),and social differentiation is not significant.(3)The influence of anthropogenic disturbance on social network.For Xiamen population,the association index of dolphins in serve disturbance area(0.18±0.09)is weaker than that in slight disturbance area(0.25±0.13).The result showed that the disturbance of anthropogenic activities can reduce the individual relationship,and then affect the social structure of population.(4)The influence of calf presence/absence on social network.For calf presence group in Xiamen and Beibu,the average and maximum association index of individuals are higher than that of calf absence group.These supported that calf presence strengthen the association of dolphins.The calves located in the core positon of the whole social network,which plays an important role in the formation and maintenance of social structure.(5)The spatial distribution separation of group.We found that both Xiamen and Beibu populations showed spatial distribution separation to some extent.The Northeastern and Western Communities were mainly distributed in Tonan Bay and Xiamen West harbor respectively.The two groups in Beibu Gulf mainly used Dafengjiang-Nanliujiang area(including Sannian Bay)and Shatian-Caotan areas.(6)Implication to conservation.The present research suggests that both anthropogenic activities and calf presence/absence influenced the social structure.The community or group undergoing serve influence should be considered as priority protection and management unit.Accordingly,the anthropogenic activities there should be reduced or restricted.Additionally,the protection effort should be focused on calves in order to maintain strong relationship between individuals.Given limited protection effort,the priority should be given to the core distribution area protection.In present paper,we constructed the social network of Indo-Pacific humpback dolphins at Xiamen and Beibu Gulf,and clarified the association pattern of dolphins and its geographic variation.This difference may be related to local geographical environment,anthropogenic activities types and intensity,calf proportion,population size and genetic relationship.In order to explain the mechanism of social structure of Indo-Pacific humpback dolphins,it is necessary to further study habitat selection,the influence of vessels and genetic relationship on social structure.