Chapter V 



MARINE MAMMAL STRANDINGS AND DIE-OFFS 



Over the past decade and a half, there has been an 

 increase in the incidence of unusual marine mammal 

 mortalities throughout the world. These incidents 

 have occurred in widely separated areas and have 

 involved a variety of marine mammal species, includ- 

 ing monk seals in the northwestern Hawaiian Islands, 

 harbor seals in New England, manatees in Florida, 

 and humpback whales in Cape Cod. Among the 

 largest and most publicized were the deaths of more 

 than 700 bottlenose dolphins along the U.S. mid- 

 Atlantic coast in 1987 and early 1988, and more than 

 17,000 harbor seals in the North Sea later in 1988. 



As noted in the previous Annual Report, there 

 were two incidents of higher-than-normal bottlenose 

 dolphin mortality in the Gulf of Mexico in 1990. 

 There also was a catastrophic die-off of striped 

 dolphins in the Mediterranean Sea. These events and 

 the role played by the Commission and its Committee 

 of Scientific Advisors in efforts to determine the cause 

 and biological significance of these events are de- 

 scribed in past Aimual Reports. 



Unusual Eyents Occurring in 1991 



During 1991, the die-off of striped dolphins in the 

 Mediterranean that began in mid- 1990 continued to 

 spread east. In addition, an unusually high number of 

 seals died in Long Island Sound, an outbreak of lepto- 

 spirosis occurred in California sea lions in northern 

 and central California, and there were indications of 

 a possible fungal infection in dolphins along the south- 

 east Florida coast. In each case, the Commission, in 

 consultation with its Committee of Scientific Advisors, 

 reviewed available information and provided guidance 

 or other assistance to the organizations investigating 

 the events. 



Striped Dolphin Die-Off 

 in ttie Mediterranean Sea 



As described in the previous Annual Report, nearly 

 750 dead striped dolphins {Stenella coeruleoalba) 

 were recover«l from the Mediterranean coasts of 

 Spain, France, and Italy during the last six months of 

 1990. Additional dead dolphins were reported in 

 other parts of the western Mediterranean, suggesting 

 that the actual mortality was substantially higher. The 

 Commission provided funds in 1990 for two marine 

 mammal veterinarians experienced in investigating 

 such mortalities to conduct a site visit and consult 

 researchers carrying out the investigations. It also 

 provided supplemental support to help Spanish investi- 

 gators determine the cause of the incident. 



During the first half of 1991, the striped dolphin 

 die-off decreased in intensity. However, dead dol- 

 phins began to be recovered farther to the east. From 

 June through September 1991, 198 dead striped 

 dolphins were recovered from Italian waters, primari- 

 ly along the southern Adriatic coast. By early Sep- 

 tember, the die-off had reached Greece, where at least 

 35 dead animals were reported by early November. 



The most up-to-date results of the continuing 

 investigations were reviewed at a workshop held in 

 Spain on 4-5 November 1991. The workshop, 

 sponsored by the Greenpeace International Mediterra- 

 nean Sea Project, included scientists who had worked 

 on the previously mentioned die-offs of bottlenose 

 dolphins, harbor seals, and manatees, as well as 

 scientists investigating the striped dolphin die-off. 

 Workshop participants concluded that the striped 

 dolphin die-off probably was being caused by a 

 previously unknown morbillivirus, tentatively referred 

 to as delphinoid distemper virus. A similar morbilli- 

 virus (phocine distemper virus) caused the mass 

 mortality of harbor seis in the North Sea in 1988. 



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