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Humpback Dolphins in Hong Kong and the Pearl River Delta: Status, Threats and Conservation Challenges

Authors:
  • WWF Hong Kong

Abstract and Figures

In coastal waters of the Pearl River Delta (PRD) region, the Indo-Pacific humpback dolphin (Sousa chinensis) is thought to number approximately 2500 individuals. Given these figures, the putative PRD population may appear strong enough to resist demographic stochasticity and environmental pressures. However, living in close proximity to the world's busiest seaport/airport and several densely populated urban centres with major coastal infrastructural developments comes with challenges to the long-term survival of these animals. There are few other small cetacean populations that face the range and intensity of human-induced pressures as those present in the PRD and current protection measures are severely inadequate. Recent mark-recapture analyses of the animals in Hong Kong waters indicate that in the past two decades the population parameters have not been well understood, and spatial analyses show that only a very small proportion of the dolphins’ key habitats are given any form of protection. All current marine protected areas within the PRD fail to meet a minimum habitat requirement that could facilitate the population's long-term persistence. Demographic models indicate a continuous decline of 2.5% per annum, a rate at which the population is likely to drop below the demographic threshold within two generations and lose 74% of the current numbers within the lifespan of three generations. In Hong Kong, the case of humpback dolphins represents a particularly explicit example of inadequate management where a complete revision of the fundamental approach to conservation management is urgently needed.
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    
     
  

 

     
 
     
  
   
     
     
  
          
 
  
  

               
     
          
        
            
         
     
     

  
   
      
   
     
    
     
     
  
        
   
       
     
      
      
        
   
     
        
    


    
   
 
 

             
           
           
          
          
          
             
            
           
            
              
             
             
         
                
            
              
         
         
 
 
        
         
           
           
         
           
             
           
          
           
          
    
         
         
          
          
            
         
           
     
          
         
         
          
           
            
            
           
         
         
          
          
     
  
           
           
            
           
       
        
         
             
        
          
            
           
             
   
         
             
            
         
           
           
          
             
    
              
 
   
 

    
    
    
    
    
    
    
    
    
    
     
         
     
     

  
 
 
        
            
           
              
            
             
         
           
         
      
  
        
          
          
         
         
           
           

           
          
           

    
        
         
             
         
            
           
            
          
         
           
       
           
          
         
        
          
        
          
            
    
            
         
         
  
    
         
           
       
         
         
           
          
        
          
        
            
        
       
        
         
       
          
          
        
      
         
           
          
            
            
            
    
       
             
         
        
          
             
          
           
          
          
       
         
            
          
         
         
           
         
          
            
            
            
          
         
            
      
   
         
          
        
          
          
          
         
         
           
        
          
         
         
         
           
         
             
         
             
            
            
      
         
        
          
         
            
         
          
           
            
         
          
        
           
     
         
            
            
          
             
         
           
            
         
         
         
        
         
           
          
    
          
         
    
        
          
         
          
            
           
         
           
            
           
        
           
            
            
          
       
         
           
           
          
           
          
          
         
         
  
    
           
             
          
             
          
           
         
           
             
         
        
            
         
            
           
        
           
          
          
       
           
 
          
           
       
         
         
    
       
            
           
          
          
         
      
        
          
         
         
      
          
         
          
            
       
           
          
            
              
          
           
          
           
         
          
             
           
         
         
          
           
          
             
          
             
           
         
         
          
            
             
           
            
    
           
          
          
         
         
          
   
    
        
        
         
        
           
          
         
           
          
            
            
          
           
               
         
         
        
        
     
          
       
  
           
           
            
          
        
        
   
            
            
         
            
           
             
           
           
           
          
            
      
 
         
          
        
         
          
     
 
         
        
        
           
         
    
           
          
         
            
          
         
            
        
          
      
          
          
            
         
          
        
         
        
            
         
      
           
          
          
           
         
        
          
         
           
           
           
            
          
           
         
         
         
          
         
          
             
           
         
         
    
        
           
         
           
         
          
            
        
         
          
          
         
            
    
  
        
         
            
          
         
         
         
             
        
            
           
          
           
          
           
    
    
           
           
         
            
          
       
          
            
       
         
           
      
      
            
        
     
        
            
          
         
            
          
             
             
            
            
            
         
         
        
           
       
          
            
           
             
            
         
          
   
              
          
          
      
     
        
   
   
   
         
           
        
 
           
             
           

    
    
          
           
        
            
            
       
            
           
          
      
      
   

         
           
             
           
        
    
        
             
            
          
           
    
         
          
              
           
           
           
     
          
            
          
           
         
        
   
              
          
             
          
  
         
            
        
            
          
          
         
         
      
            
         
            

    
             
           
         
          
        
         
         
         
        
           
            
            
    
     
          
         
            
            
          
         
           
            
         
    
         
            
        
           
         
           
   
     
        
          
           
         
         
           
         
          
             
           
          
        
    
           
            
          
           
          
         
           
       
           
          
         
            
          
        
            
        
         
        
         
         
          
          
        
         
           
          
     
         
          
         
         
          
          
          
            
          
            
         
              
             
        
           
          
          
           
         
           
      

           
            
             
           
         
            
           
    
           
            
      
        
          
         
           
         
          
         
         
       
         
            
          
         
         
           
          
          
          
     
           
         
       
        
            
          
       
       
        
        
           
           
       
             
      
           
          
         
         
              
           
        
           
             
        
           
  
  
    
         
        
            
        
        
       
   
   
       
    
   
         
  

         
 
           
        
          
         
        
          
         
       
        
           
          
        
          
          
    
          
           
            
         
         
        
          
          
             
          
              
          
         
          
           
         
           
            
           
         
          
           
             
         
          
         
           

        
          
          
         
           
          
           
           
          
          
            
         
          
           
           
             
              
       
         
          
            
            
            
            
              
         
           
         
             
    
           
             
              
        
          
              
          
         
 
   
       
         
          
           
           
           
          
           
         
        
           
            
        
              
           
          
           
  
            
         
     
          
          
         
         
            
           
         
              
           
          
   
           
          
           
       
         
          
             
            
            
         
   
            
          
           
        
          
          
          
           
             
          
        
         
  
       
         
            
         
          
        
       
           
        
      
          
    
           
            
           
        
          
          
   
  
           
           
          
          
            
         
             
            
         
          
         
           
         
          
          
          
            
            
           
       
           
             
             
         
          
           
        
         
             
         
             
         
  

             
       
        
         
           
          
            
            
            
  

           
        


            
    
     
        
        
  
     
         
     
   
     
               
             
         
        
     
            
          
           
              
 
   
             
          
         
           

    
           
          
         
           
 
          
      
               
              
     
             
          
     
               
          
    
            
           
   
            
         
  
  
             
           
          
           
     
           
          
              
             
    
             
         
    
           
         
           
           
         
         
        
        
          
     
         
     
       
            
         
    
         
             
            
           
          
     

                
        
        
              
        
             
        
         
 
                
          
     
                
          
        

           
          
           
   
            
           
          
             
        
            
      
        

      
          
            
        
      
               
          
     
           
            
 
            
       
            
          
    

    
    
            
         
    

     
            
         
    

     
           
           
          
        
       
             
           
           
   
             
       
           
    
          
  
  
            
         
 
           
     
            
          
       
          
          
            
 
          
            
 
            
            
      
    
        
          
 
             
            
 
             
 
         
           
          
          
      
            
        
          
    
              
          
         
  
       
            
            
 
             
            
          
        
          
         
    
           
      
             
     
           
        
         
         
             
           
        
    
           
             
       
               
          
         
         
           
       
            
       
           
              
 
      
      
     
      
     
           
          
    
           
       
            
          
   
           
        
           
             
  
             
           
         
         
    
  
          
         
          

       
               
          
            
   
             
        
           
     
     
              

          
      
           
           
            
          
         
          
              
     
          
         
            
          
     
        
       
          
    
           
          
         
         
          
           
            
     
   
           
            
            
      
          
       
           
          
   
          
         
            
    
         
         
         
            
      
  
  
        
         
             
             
           
   
           
 
             
           
   
        
 
            
        
         
            

            
         
    
             
          
          
           
 
          
          
     
    
             
            
     
                
              
     
                
         
          
   
            
    
           
            
    
    
            
          
  
             
           
          
           
 
              
              
          
           
           
  
          
   
            
          
          
     
       
           
        

       
                 
        
          

              
          
            
            

    
         
                
          
 
          
             
       
        
 
            
          
      
                
            
            
               
             
             
         
         
     
       
    
... This means that they can serve as a pre-warning system for the evaluation of aquatic ecosystem health (Bossart, 2011;Evans et al., 2005;Jessup et al., 2004;Moore and Read, 2008;Wells et al., 2005). Indo-Pacific humpback dolphins (Sousa chinensis) inhabit coastal or estuarine waters where they are greatly influenced by human activities (Karczmarski et al., 2015). According to the International Union for Conservation of Nature (IUCN) criteria delimiting the endangerment levels of species, Indo-Pacific humpback dolphin populations are currently listed as "Vulnerable" (Rako-Gospic et al., 2017) in the Red Species List Level (Jefferson et al., 2017). ...
... According to the International Union for Conservation of Nature (IUCN) criteria delimiting the endangerment levels of species, Indo-Pacific humpback dolphin populations are currently listed as "Vulnerable" (Rako-Gospic et al., 2017) in the Red Species List Level (Jefferson et al., 2017). As a metropolitan area with the fastest economic development around the world, the Pearl River Estuary (PRE) is a very busy zone, with probably the most intensive human activities globally (Halpern et al., 2015;Karczmarski et al., 2015). The shallow water of the PRE is inhabited by the largest population of humpback dolphins worldwide, which has been predicted to have been depleted and inevitably subjected to the cumulative effects of multiple anthropogenic threats (Chen et al., 2010;Wang et al., 2012). ...
... Major anthropogenic disturbances affecting the long-term survival of PRE humpback dolphins include maritime traffic (shipping activities), exposure to pollutants, and competition for food resources with local fisheries (Karczmarski et al., 2015). With the vigorous development of maritime transportation and marine fisheries, PRE humpback dolphins often experience physical trauma caused by vessel collisions, propeller strikes, or fishing gear entanglement (Hung, 2008). ...
Article
With the dramatic increase in anthropogenic threats to the Pearl River Estuary (PRE), the population size of the Indo-Pacific humpback dolphins (Sousa chinensis) has significantly decreased over the past decade. To understand the impact and potential risks of intense human activities on these dolphins, factors related to the mortality of humpback dolphins in the PRE were investigated by a detailed examination of 343 dolphin specimens stranded during 2003–2017. There was a significant (p < 0.01) increasing trend for humpback dolphin stranding, reflecting the accelerating rate of the population decline. A large proportion of strandings (35.88%) were neonates. A low recruitment rate implies slow population growth, and hence, limited capacity to resist anthropogenic stress. The most commonly diagnosed causes of death were vessel collision and net entanglement. The concentrations of trace metals, polychlorinated biphenyl (PCB) congeners, dichlorodiphenyltrichloroethane, polycyclic aromatic hydrocarbons, and most of per- and polyfluoroalkyl substances (PFASs) in the dolphin samples were greater than those previously reported in cetaceans globally. Furthermore, Cu, PCB77, PCB169, PCB81, PCB37, and PFASs (excluding PFBA, PFPeA, PFHxA, PFHxDA, and PFODA) were the major pollutants accumulated in neonates. 67% of PCB, 78% of Cu, and 100% of perfluorooctane sulfonate concentrations in the neonates exceeded the threshold for toxicological effects in marine mammals, suggesting that these compounds could be important factors contributing to the low survival rate of calves in this area. This study revealed that vessel transportation, fishing activities, and pollutant bioaccumulation are the three major causes of humpback dolphin mortality in the PRE. These results highlight the need for more efforts to restrict anthropogenic activities, especially vessel traffic, the catching of these marine animals and fishing, and pollutant discharge, in order to prevent vulnerable species from continuous population decline and further extinction.
... Humpback dolphins inhabiting PRD waters are among the most anthropogenically impacted coastal delphinids known to science, while local and regional conservation efforts are hampered by poor management decisions and insufficient scientific evidence (Wilson et al. 2008;Jefferson et al. 2009;Karczmarski et al. 2016). Their population ecology has only recently been rigorously quantified (e.g. ...
... This issue, however, was largely overlooked in previous studies and conservation analyses of the PRD humpback dolphins (e.g. Jefferson 2000; Wilson et al. 2008;Jefferson & Smith 2016;Karczmarski et al. 2016;Miller 2016), primarily because of the difficulties in gaining access to sufficiently representative samples. The only previous dietary study of the PRD humpback dolphins (Barros et al. 2004) was limited to small sample size (n = 15) and incomplete population coverage, as it only had access to stomach contents retrieved from carcasses stranded in Hong Kong. ...
... As stomach contents represent a snapshot of individual feeding habits and findings from an individual stomach may be biased towards the prey available at its stranding site/region (Ambrose et al. 2013), spatial factors and representatively wide geographic range have to be considered, especially when studying highly mobile animals (Owen et al. 2011). In the PRD, to be representative the geographic range has to include not only diverse environmental features but also a spatial pattern (or gradient) of anthropogenic impacts, as they likely cause varying degree of stress acting on the marine biota (Sanderson et al. 2010;Green et al. 2016;Karczmarski et al. 2016). In the study reported here, dolphin carcasses were recovered across almost the entire coastal zone of the PRD (∼150 km of a straight linear west-to-east distance, which represents over 1000 km of highly diverse coastline), hence it is well representative of the species as well as the geographic region. ...
Article
The Pearl River Delta (PRD) region on the southeast coast of China has long been known as a highly productive fishing ground. Since the late 1980s, fishing pressure in the PRD has been intense, which warrants concerns of potential fishery-related impacts on the food resources and foraging ecology of apex marine predators in this region, such as the Indo-Pacific humpback dolphin (Sousa chinensis). In this study, we examined 54 stomachs with food remains, collected from beached carcasses of humpback dolphins recovered during fifteen years between 2003 and 2017. The 6043 identified prey items represent 62 teleost taxa, primarily small estuarine fish, but also larger reef fish. The dolphins appear to be opportunistic foragers, hunting across the water-column, with preference for shoaling and meaty fishes (e.g. Chrysochir aureus IRI% = 38.6%, Johnius belangerii IRI% = 23.1%, Mugil cephalus IRI% = 14.0%). Our findings suggest a dietary shift in recent years, from primarily demersal (as previously reported) to greater intake of neritic and pelagic fish. Dolphin foraging group size has decreased in recent years, which corresponds with declining size and numbers of prey items retrieved from dolphin stomachs. We suggest that these are indicators of declining food resources. Faced with a shortage of preferred prey, humpback dolphins may have broadened their dietary spectrum to maintain their daily energy intake, while their foraging group size decreased in response to the altered tradeoff between the costs and benefits of group foraging. This article is protected by copyright. All rights reserved
... Nothing will save or reverse the decline of an animal or group of animals, or plants for that matter, if their habitat becomes difficult to live in or unlivable. For marine mammals, this can be wholesale nearshore destruction of habitat, as is occurring in some areas of the Pearl River Estuary for Indo-Pacific humpback dolphins, Sousa chinensis (Jefferson et al. 2008;Karczmarski et al. 2016). It can be entanglement in fishing lines and nets, some of them discarded or lost, other sources of macro-pollution, and direct strikes by fast-moving large vessels, as witness the visible decimation of North Atlantic right whales that are now on the brink of extinction (Kraus and Rolland 2007;Reeves 2022, this volume). ...
... Nothing will save or reverse the decline of an animal or group of animals, or plants for that matter, if their habitat becomes difficult to live in or unlivable. For marine mammals, this can be wholesale nearshore destruction of habitat, as is occurring in some areas of the Pearl River Estuary for Indo-Pacific humpback dolphins, Sousa chinensis (Jefferson et al. 2008;Karczmarski et al. 2016). It can be entanglement in fishing lines and nets, some of them discarded or lost, other sources of macro-pollution, and direct strikes by fast-moving large vessels, as witness the visible decimation of North Atlantic right whales that are now on the brink of extinction (Kraus and Rolland 2007;Reeves 2022, this volume). ...
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Confronted with the ruinous consequences of human presence for Earth and its biodiversityBiodiversity, human societyHuman society starts to feel the imperative for acting to stem such consequences, and the accompanying loss of species. Here, we address the case of conservingConservingmarine mammalsMarine mammals, a group of species that have a special place in the hearts and minds of humans—thanks to the behavioral and cognitive abilitiesCognitive abilities possessed by many of these species and because some of them are highly social. However, does marine mammal conservationConservation work? Some notable gains have been achieved in recent decades that need to be viewed from the perspective of a somber background of losses and precipitous declines. As we assess successes against failures, we realize that there is no “one size fits all marine mammal conservationConservation” in a world so deeply affected by the intricacies of human relationships with the biosphere. We also argue that simply conservingConserving species or populations and their habitatsHabitat is not enough, as the culturesCulture of such species and populations also have high conservationConservation relevance. Furthermore, it is not only the animals’ physical well-beingWell-being that deserve attention but also the maintenance of their psychological healthHealth: there seems to be little point in maintaining stable populations if survivalSurvival for individuals requires a constant struggle to avoid fishing gearFishing gear, prey depletionPrey depletion, ship strikesShip strike, shipstrikes, intolerable noiseNoise levels, and chemical intoxication. We fear that future marine mammal conservationConservation efforts may be insufficient to prevent the disappearance of some populations and even species, while some others will have managed to flourish in a changed environmentEnvironment. Without falling into the trap of losing hope, the marine mammalMarine mammalsconservationConservationcommunityCommunity should at least help steer the dynamics toward such “new normal” which is as similar as possible to the “old normal,” without forgetting baselines of the past and while refusing to constantly accept new baselines of an ever-diminished natural Earth.
... In Taiwan, the habitat of this dolphin is mainly concentrated around the central section of the west coast, ranging within a narrow strip from the Longfeng Harbor in Miaoli to the General Harbor of Tainan county, mainly within 3 km of land, in water at a depth of less than 20 m (Chou et al., 2014Chou, 2018). In addition, its habitat has often been described as including estuarine areas (Dares et al., 2014;Chen et al., 2016;Karczmarski et al., 2016). Jefferson and Hung (2004) suggested that the range of the Indo-Pacific humpback dolphin is mainly dependent on the abundance of food resources. ...
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The Indo-Pacific humpback dolphin ( Sousa chinensis ) has been reported to prefer estuary habitats. This study explored the environmental factors affecting a critically endangered population off the coast of Yunlin, Taiwan. We measured dolphin sighting rates and estuary characteristics affected by the watershed, including seven physical factors (watershed rainfall, watershed runoff, estuarine turbidity, pH, salinity, temperature, and dissolved oxygen) and two biological factors (estuarine net primary production and chlorophyll a concentration), at the Hsinhuwei River estuary in Taiwan. Dolphin activity was measured by sighting rate and behavioral indices for feeding and traveling between 2017 and 2018. We observed that when the maximum net production increased alongside rising temperatures in spring, both the dolphin sighting rate and foraging activity increased. This trend was maintained until heavy rainfall or increased river runoff occurred during late summer, which resulted in high turbidity in autumn and winter. Turbidity was significantly negatively correlated with dolphin activity (sighting rate and foraging). Furthermore, we found that dolphin traveling positively correlated with the chlorophyll a concentration and maximum net production factors, which could attract dolphins expecting more abundant prey fish in the estuary supported by the high primary production. This study provides empirical evidence on how estuary characteristics affected by the watershed can affect the sighting rate and behavioral activities of Indo-Pacific humpback dolphins.
... However, a recent demographic study predicted that this population would be declining at about 2.46% per annum (Huang et al., 2012). Studies from our groups showed that humpback dolphins inhabiting the PRE bioaccumulated excessively high levels of OCs compared with dolphins from other regions, which might have caused longlasting effects on their survival and population evolution (Gui et al., 2018a;Karczmarski et al., 2016;Wu et al., 2013). It is reasonable to speculate that the observed high neonatal mortality rates in the PRE dolphins might have been largely due to the anthropogenic contamination effects on the early life stages of this species (Jefferson et al., 2006;Parsons, 2004;Sun et al., 2017). ...
Article
The placental transfer and congener composition of organic contaminants (OCs) in Indo-Pacific humpback dolphins have been little studied. In the present study, 16 polycyclic aromatic hydrocarbons (PAHs), 18 organochlorine pesticides (OCPs), and 28 polychlorinated biphenyl (PCB) congeners were analyzed in muscle, lung, liver, kidney, and blubber tissues from three mother–fetus pairs of this species stranded along the Pearl River Estuary, China. For PCBs, tetra-, penta-, hexa-, and hepta-chlorobenzene congeners were dominant in all the analyzed samples. Among them, hexachlorobenzene congeners showed the highest level in most dolphin mother-fetus tissue samples. The concentrations of PCBs and OCPs in adult females were higher in the detoxification organs (liver and kidneys) than in the muscles and lungs, whereas muscle tissues in fetuses generally exhibited higher PCBs and OCPs levels than the livers and kidneys. The most abundant PAHs in the four tissues were those with lower molecular weights, which were also the most water-soluble and bioavailable. Negative correlations between the octanol/water partition coefficients (log KOW) and the fetus/mother ratios for PCB congeners revealed that the transfer of PCBs may be determined by their lipid solubility. OCPs and PCBs with low molecular weights and low log KOW values would be more likely to accumulate in the dolphin liver, lung, kidney and muscle tissues. Furthermore, OCs with low molecular weights and low log KOW values were more concentrated in the fetal blubber, lung, and liver tissues than in their respective mothers. The ubiquitous existence of OCs in the mother–fetus pairs strongly suggested that these contaminants could pass through the placenta and partition in fetal tissue. The high transfer efficiency of PAHs and PCBs indicated that the placenta might not be an efficient barrier for these pollutants. PCBs levels in both mother and fetus dolphins could cause immunosuppression.
... According to those systematic review articles on humpback dolphins (e.g. Braulik et al. 2015;Cerchio et al. 2015;Collins 2015;Jefferson & Curry 2015;Piwetz et al. 2015;Sutaria et al. 2015;Xu et al. 2015;Hanf et al. 2016;Jefferson & Smith 2016;Karczmarski et al. 2016), the abundance (population size) was categorized into an ordered scale: small (<100), medium (100-300), and large (>300). In addition, we extracted the location information (latitude, longitude) from the relevant publications with the help of Google Earth Pro (Google Inc. ...
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Humpback dolphins (Sousa spp.) are obligate shallow‐water and resident species, and they typically live in fission‐fusion societies composed of small‐sized groups with changeable membership. However, we have scant knowledge of their behavioural ecology, starting with potential factors influencing inter‐population variability of their group sizes. Here, we compiled a new global dataset of humpback dolphin group sizes based on 150 published records. Our data indicated an inter‐specific consistency of group‐living strategy among the four species in the Sousa genus, as these species preferred living in small‐sized groups with a mean size of mostly no more than 10, a minimum size of single individual or small pairs, and a maximum size of several tens or ∼100. In addition, we clearly showed the geographic variations in group sizes of humpback dolphins at a global scale. We found that the geographic variations in humpback dolphin group sizes were primarily associated with the latitude, sea surface temperature, and abundance. To conclude, our findings provide insights into social dynamics and socioecological trade‐offs of humpback dolphins, and helps better understand how these resident animals adapted to their shallow‐water habitats from the perspectives of biogeography and socioecology. This article is protected by copyright. All rights reserved
... Their restricted habitat preference to inshore shallow waters renders them susceptible to a wide range of anthropogenic impacts (Jefferson & Smith 2016;Karczmarski et al. 2016;Li 2020), of which, in the long-term, habitat degradation and loss appear to represent the greatest threat (Lin et al. This article is protected by copyright. ...
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Indo‐Pacific humpback dolphins (Sousa chinensis) inhabit shallow coastal waters of the Indo‐Pacific region including southeast China, with at least six putative populations identified to date in Chinese waters. However, the connectivity among these populations has not yet been investigated. In the present study, we compared and cross‐matched photographic catalogs of individual dolphins collected to date in the Pearl River Delta region, Leizhou Bay, Sanniang Bay, and waters southwest of Hainan Island, a total of 3158 individuals, and found no re‐sighting of individual dolphins among the four study areas. Furthermore, there was a notable difference in the pigmentation pattern displayed by individuals from these four regions. We suggest that this may be a phenotypical expression of fine‐scale regional differentiation among humpback dolphin groups, possibly distinct populations. Given the considerable conservation management implications it may carry (e.g. definition of management units), further research is much needed. This article is protected by copyright. All rights reserved
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As IUCN critically vulnerable species,the Indo-Pacific humpback dolphins ( Sousa chinensis ) have attracted great public attention in recent years. The threats of human disturbance and environmental pollution to this population have been documented extensively. However, research on the sensitivity of this species to climate change is lacking. To understand the effect of climate change on the potential distribution of Sousa chinensis , we developed a weighted ensemble model based on 82 occurrence records and six predictor variables (e.g., ocean depth, distance to shore, mean temperature, salinity, ice thickness, and current velocity). According to the true skill statistic (TSS) and the area under the receiver operating characteristic curve (AUC), our ensemble model presented higher prediction precision than most of the single-algorithm models. It also indicated that ocean depth and distance to shore were the most important predictors in shaping the distribution patterns. The projections for the 2050s and 2100s from our ensemble model indicated a severe adverse impact of climate change on the Sousa chinensis habitat. Over 75% and 80% of the suitable habitat in the present day will be lost in all representative concentration pathway emission scenarios (RCPS) in the 2050s and 2100s, respectively. With the increased numbers of records of stranding and deaths of Sousa chinensis in recent years, strict management regulations and conservation plans are urgent to safeguard the current suitable habitats. Due to habitat contraction and poleward shift in the future, adaptive management strategies, including designing new reserves and adjusting the location and range of reserves according to the geographical distribution of Sousa chinensis , should be formulated to minimize the impacts of climate change on this species.
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The conservation of humpback dolphins, distributed in coastal waters of the Indo-West Pacific and eastern Atlantic Oceans, has been hindered by a lack of understanding about the number of species in the genus (Sousa) and their population structure. To address this issue, we present a combined analysis of genetic and morphologic data collected from beach-cast, remote-biopsied and museum specimens from throughout the known Sousa range. We extracted genetic sequence data from 235 samples from extant populations and explored the mitochondrial control region and four nuclear introns through phylogenetic, population-level and population aggregation frameworks. In addition, 180 cranial specimens from the same geographical regions allowed comparisons of 24 morphological characters through multivariate analyses. The genetic and morphological data showed significant and concordant patterns of geographical segregation, which are typical for the kind of demographic isolation displayed by species units, across the Sousa genus distribution range. Based on our combined genetic and morphological analyses, there is convincing evidence for at least four species within the genus (S. teuszii in the Atlantic off West Africa, S. plumbea in the central and western Indian Ocean, S. chinensis in the eastern Indian and West Pacific Oceans, and a new as-yet-unnamed species off northern Australia).
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The taxonomic status of humpback dolphins (genus Sousa, sub-family Delphininae) is unresolved. While the classification of this genus ranges from a single to three nominal species, the International Union for Conservation of Nature and the International Whaling Commission only recognise a ‘two-species’ taxonomy (S. teuszii in west Africa, and S. chinensis in the Indo-Pacific). Under the IUCN (2008), S. chinensis is listed as ‘near threatened’, but is only considered as a ‘migratory’ species in Australia. Taxonomic resolution of the genus Sousa is needed to define particular conservation status and develop appropriate management actions. Using phylogenetic analyses of 1,082 bp of mitochondrial and 1,916 bp of nuclear DNA, we provide multiple lines of genetic evidence for the genetic distinction of S. chinensis in China and Indonesia from S. chinensis in Australia. The separation of Australian Sousa from Sousa of Southeast Asia requires a review of their current conservation status and respective management actions.
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The Indo-Pacific hump-backed dolphin (Sousa chinensis Osbeck, 1765) is found throughout the western Pacific and Indian oceans, from southern China and northern Australia in the east to South Africa in the west. Throughout most of its range it has not been well studied, and in southern China very little is known of its biology. The goal of the present study was to provide scientific information needed for the long-term conservation and management of the population that occurs in Hong Kong waters. From September 1995 to November 1998, 38,105 km of systematic line transect surveys were conducted throughout marine waters of the Hong Kong Special Administrative Region (SAR) of the People's Republic of China (PRC) and adjacent waters to provide data on distribution and abundance. Photo-identification of individual dolphins allowed for examination of movement patterns, home ranges, and social organization. Collection of stranded dolphin carcasses and detailed necropsies provided information on causes of death as well as samples for life history studies, such as feeding habits, growth and reproduction, ecotoxicology, and stock structure. The dolphin population appears to be centered around the Pearl River Estuary, and Hong Kong waters represent the eastern portion of the range, which extends far into mainland Chinese waters (Lingding Bay) and covers at least 1,800 km2. Within Hong Kong, dolphins only occur in western waters around Lantau Island. The area north of Lantau Island is heavily used throughout the year and represents by far the most important habitat in Hong Kong. Line transect analyses indicate that between 88 (spring) and 145 (summer). dolphins occur in Hong Kong. Based on 27,600 photographs taken, 213 individual dolphins were identified. The total size of the Pearl River breeding population is unknown, but is estimated to consist of at least 1,028 dolphins, based on line transect analysis. An apparent decline in the number of dolphins in the North Lantau area over the period from 1996-1998 was not statistically significant. Individual dolphins have overlapping home ranges of about 30-400 km2 in different sections of the population's overall range. Groups of dolphins in Hong Kong number up to 23 animals, with an average group size of 3.8 ± s.d. 3.63 animals. There is no significant seasonal variation in group size, but groups feeding behind pair trawl fishing vessels (mean = 9.6 ± s.d. 5.37) are significantly larger thane other groups, and groups in Lingding Bay, in Chinese waters west of Hong Kong (mean = 8.3 ± s.d. 7.84) are significantly larger than those in Hong Kong. Groups are very fluid and change composition frequently, with association indices ranging from 0-0.333. Behavioral patterns are similar to those of other coastal dolphins, but Hong Kong hump-backed dolphins only rarely ride bow waves. Following pair trawlers represents an important feeding strategy for some individuals. Construction work on an airport fuel facility in the dolphins' main habitat appears to have caused some disturbance (indicated by increased swimming speeds) and possibly temporary evacuation of the surrounding area. There is a great deal of developmental variation in the color pattern of southern Chinese hump-backed dolphins, with a general lightening from newborn to adult stages. Males appear to retain more spots in adulthood than females. Length at birth appears to be about 100 cm, and postnatal development is characterized by rapid growth in the first year and a levelling-off of the growth curve after reaching adulthood. Asymptotic length is reached at around 243 cm. Length and weight are related exponentially, with the maximum weight about 250 kg. Calving occurs throughout the year but most young are born from January through August, with a peak in spring/summer. Scant evidence suggests that sexual maturity in females is reached at about 9-10 years of age. Dolphins feed mainly on several demersal and pelagic fish species that are often associated with estuaries. There is a lack of evidence for long-distance movements (on the order of hundreds of linear kilometers), and this presumably results in isolation of groups around major Chinese fiver mouths. Thus it appears that there may be at least 8 separate populations of hump-backed dolphins along the coast of southern China. The Pearl River Estuary, including Hong Kong, is apparently inhabited by one of these populations, although preliminary genetic work has shown only equivocal evidence of population separation from dolphins in the Xiamen area. Human-related causes of mortality include entanglement in fishing nets and vessel collisions. Some environmental contaminants (especially the heavy metal mercury and the pesticide DDT) were found in high levels in some dolphins, and preliminary evidence suggests that these may be affecting the health of the animals. A series of recommendations for management and for further research have been made to aid in the conservation of these animals. Principles for the conservation of wild living resources should be followed, and information from both the natural and social sciences are needed for proper management. Research and long-term monitoring of the population must continue for management strategies to be evaluated and refined. Overall, the population of hump-backed dolphins that occurs in Hong Kong waters appears to be viable and should be able to survive with appropriate conservation efforts.
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A three-component competing-rick model for animal mortality is presented, in which the additive hazards include a new model, dominant during the prematurity period; a constant hazard, dominant during the period of maturity; and the conventional Gompertz hazard, dominant during senescence. A good fit of the model is obtained to survival data for a variety of species, with both laboratory and field data being represented. Interpretation of the model parameters in terms of animal adjustment to hazards is offered.
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The taxonomy of the humpback dolphin genus Sousa has been controversial and unsettled for centuries, but recent work indicates that there are several valid species. A review of multiple lines of evidence from skeletal morphology, external morphology, coloration, molecular genetics, and biogeography, in combination provides strong support for the recognition of four species of Sousa. These include S. teuszii (Kükenthal, 1892), a species with uniform gray coloration and a prominent dorsal hump, which is found in the Atlantic Ocean off West Africa. The species S. plumbea (G. Cuvier, 1829) has similar external appearance to S. teuszii, but has a more pointed dorsal fin. It occurs in the Indian Ocean from South Africa to Myanmar (Burma). The original taxon, S. chinensis (Osbeck, 1765), is reserved for the species that has a larger dorsal fin with no prominent hump, and largely white adult coloration. It ranges from eastern India to central China and throughout Southeast Asia. Finally, we describe a new species of Sousa, the Australian humpback dolphin, which occurs in the waters of the Sahul Shelf from northern Australia to southern New Guinea. It has a lower dorsal fin, more extensive dark color on the body, and a dorsal “cape.” It is separated from the Indo-Pacific humpback dolphin by a wide distributional gap that coincides with Wallace's Line.
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Estimating the degree of isolation or gene flow is central to understanding population dynamics and conservation. In this study, we used both mitochondrial and nuclear markers to investigate the genetic structure of Indo-Pacific humpback dolphins (genus Sousa) in China. Contrary to previous photo-identification and genetic studies, we found no evidence for population genetic structure or inter-population gene flow across the geographical scale examined. Significant inbreeding, which seems to support genetic isolation to some extent, was within expectation as a result of low genetic diversity in a random-mating system. Overall, the Indo-Pacific humpback dolphins in China were characterized by low genetic diversity on both maternal and bi-parental markers. While significant steps have been taken towards implementing marine reserves, our study highlights the critical need for fine-scale genetic and ecological monitoring programs and a coordinated approach to secure the survival of Indo-Pacific humpback dolphins in Chinese waters.
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Hepatic butyltin concentrations were determined in 63 cetaceans belonging to 14 species and four pinnipeds belonging to two species collected from North Pacific and Asian coastal waters. Butyltin compounds (BTs) including tributyltin (TBT), dibutyltin (DBT), and monobutyltin (MBT) were detected in almost all the liver samples suggestive of its worldwide distribution. The elevated residues detected in coastal species and low concentrations found in off-shore species indicate a high degree of butyltin contamination in coastal waters than in the open sea. Mam mals inhabiting waters of developed nations were found to contain higher BT concentrations compared with those collected from the waters proximal to developing countries. These observations strongly suggest serious BT contamination in the waters of developed countries than in developing nations at present. Among the samples collected off Japanese coastal waters, lower BT concentrations were found in pinnipeds compared with the cetaceans, sug gestive of a possible difference in degradation capacities and excretory moulting between these two groups of animals. The estimated concentration ratio of BT in the liver of killer whale fetus to its pregnant mother was relatively low (0.015), indicative that transplacental transfer of BTs from the mother to her fetus is a deal less. Among the BT breakdown products, DBT was predominant in most of the liver samples analyzed, followed by TBT and MBT.
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With a long history of mercury mining and use and a rapidly growing economy that relies heavily on coal for heat and energy, China faces an enormous challenge to reduce pollution from this toxic metal. The authors delineate what is known about the extent of the problem, regulatory steps are being taken to reduce mercury pollution, and next steps for environmental researchers. It addresses issues of mercury pollution from mercury and gold mining, coal combustion and the chemical industry. Data on dietary intake of mercury is also reported. 50 refs., 2 figs., 2 photos.
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Indo-Pacific bottlenose (Tursiops aduncus) and humpback dolphins (Sousa chinensis) off the south coast of Zanzibar, East Africa, have been subject to both direct and indirect takes as well as disturbance from local dolphin tourism during the last decade. Meanwhile, little or no information on population parameters exists for these animals. In order to assess the anthropogenic threats, a study was conducted between 1999 and 2002 to determine population sizes, distribution, and behavior of these animals. Population sizes were calculated for each year using mark-recapture methods applied to photo-identification data. The estimates ranged between 136 and 179 for the bottlenose dolphins and between 58 and 65 for the humpback dolphins in the calculated 26 km2 study area. Patterns in distribution and behavior were investigated using image and spatial statistic software on data from boat surveys. Analyses of spatial densities showed that both species concentrated their activities to smaller areas (2%–11.5%) within the study area. When the study results were considered in light of the anthropogenic threats, it was clear that immediate conservation measures were needed. This is critical if the negative impact on the species is to be minimized and the dolphins are to continue to represent a socioeconomic resource in the region.