The investigation indicated that both coastal-migratory and 

 offshore stocks of bottlenose dolphins may have been affected by 

 the die-off. However, the best available information suggests 

 that the primary impact was on the central, coastal-migratory 

 stock that ranges from Florida to New Jersey. The magnitude of 

 the population declines from the die-off remains uncertain due to 

 a lack of data and imprecision in estimates of natural mortality 

 rates. Nevertheless, the Service estimates that the die-off 

 resulted in a decline in the coastal-migratory stock of more than 

 50 percent. 



Tissues from 143 dolphins were analyzed for organochlorines 

 and heavy metal compounds as part of the Service's investigation. 

 The results were highly variable. Some animals had among the 

 highest levels of PCB contamination ever recorded in marine 

 mammals, while in others, contaminant levels were no higher than 

 those observed in healthy dolphins. Based upon the available 

 evidence, the Service concluded that pollutants were unlikely to 

 have been the proximate cause of the die-off. It is possible 

 that pollutants could have contributed to dolphin mortalities, 

 but, as theorized by Dr. Geraci in his report to the Service, 

 something else, such as a biotoxin, would have had to stress the 

 dolphins and trigger the release of contaminants from tissues 

 where they were accumulated. 



The report indicates that the die-off was restricted almost 

 exclusively to bottlenose dolphins. One spotted dolphin and one 

 striped dolphin were the only other marine mammals identified as 

 having died from the epidemic. 



The Service indicated in its letter to Congress that it was 

 continuing to investigate the causes and effects of the die-off. 

 The Service is in the process of collecting all specimen 

 materials and test results, which will be deposited with the 

 Registry of Comparative Pathology at the Walter Reed Medical 

 Center. Those materials will be made available to the scientific 

 community for further investigation. The Service also plans to 

 conduct population assessment surveys of the mid-Atlantic 

 bottlenose dolphin stock to determine more accurately the 

 magnitude of the die-off. Other survey programs, including those 

 of the Environmental Protection Agency and the Smithsonian 

 Institution, will be used to monitor the recovery of the stock. 

 In addition, the Service plans to develop a National Marine 

 Mammal Tissue Bank to store samples from stranded and/or 

 incidentally killed marine mammals for future study, particularly 

 with respect to understanding the effects of pollutants and 

 biotoxins upon living marine resources. 



Workshop on Biotoxins — The unusual dolphin mortality and 

 a somewhat similar die-off of humpback whales in Cape Cod Bay in 

 December 1987 (see the Commission's Annual Report for Calendar 

 Year 1988) raised concern that biotoxins might represent a human 



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