MARE^ MAMMAL COMMISSION — Annual Report for 1991 



Workshop participants believed that the delphinoid 

 distemper virus is distinct from the phocine distemper 

 virus and has been present, but previously undetected, 

 in the striped dolphin and other cetacean populations 

 in the Mediterranean Sea and elsewhere. That is, the 

 workshop participants doubted that the delphinoid 

 distemper virus was a mutant form of either the 

 phocine or canine distemper virus and that the dol- 

 phins had not been infected by contact with either 

 infected seals or dogs. 



Many of the striped dolphins found dead in the 

 Mediterranean Sea had secondary bacterial and fungal 

 infections, and unusually high concentrations of 

 organochlorine contaminants in blubber lipids. These 

 findings are similar to what was found in the bottle- 

 nose dolphins that died along the mid-Atlantic coast of 

 the United States in 1987 and 1988. In both cases, it 

 was judged that the contaminants were not the ulti- 

 mate cause, but may well have contributed to the 

 deaths of the animals. 



A shipboard population survey done in the western 

 Mediterranean in 1991 after the die-off had dimin- 

 ished indicated that between 115,000 and 350,000 

 striped dolphins remained in the affected population. 

 Thus, the die-off has not reduced the population to a 

 level where it is in danger of extinction. 



Seal Die-Off in Long Island Sound 



In mid-March 1991, an unusually large number of 

 seals began to wash up on beaches around Shiimecock 

 Bay, Long Island, New York. Over the next several 

 weeks, seals exhibiting similar skin lesions, thought 

 possibly to be caused by bacterial infections, came 

 ashore and died on several other beaches on the north 

 side of Long Island. They were mostly harbor seals, 

 but included three hooded seals, one gray seal, one 

 harp seal, and one ringed seal. 



Representatives of the National Marine Fisheries 

 Service briefed the Commission on the die-off during 

 the Commission's annual meeting on 25-27 April in 

 Bellevue, Washington. At that time, the remains of 

 31 animals had been recovered, all showing a similar 

 type of skin lesion. Some of the animals had fiill 

 stomachs, indicating that they died soon after eating. 

 The Service noted that the episode met four of the 



five agreed-upon criteria (see below) for deciding that 

 special investigation is merited. Accordingly, the 

 Service had initiated an investigation, and had notified 

 organizations involved in responding to strandings 

 further north to be alert to the possibility of increased 

 pinniped mortalities. 



By memorandum of 6 May 1991, the coordinator 

 of the Service's Northeast Regional Stranding Net- 

 work provided a summary of available information 

 concerning the event. At that time, the remains of 33 

 animals had been recovered. The Commission, in 

 consultation with its Committee of Scientific Advisors, 

 reviewed the sunmiary. On 13 May 1991, the Com- 

 mission recommended to the National Marine Fisher- 

 ies Service that (1) a medical director be appointed 

 immediately to oversee the medical aspects of the 

 investigation; (2) either the Gulf of Mexico Die-Off 

 Review Team or a substantial portion of the National 

 Task Group on Unusual Marine Mammal Mortalities 

 be convened as soon as possible to meet with the 

 medical director and the stranding coordinator to 

 review and evaluate all aspects of the investigation; 

 and (3) given the migratory paths of some of the 

 involved species, appropriate Canadian scientists be 

 invited to join the discussions. 



Shortly after the Commission's letter was sent, the 

 die-off abated. Tissues had been collected from many 

 of the dead seals for bacterial, contaminant, and other 

 types of analyses. At the end of 1991, the results of 

 the analyses were not yet available. 



California Sea Lion Die-Off 



In July 1991, 12 California sea lions (Zalophus 

 califomianus) stranded live or washed up dead along 

 the north-central coast of California. All animals 

 were diagnosed as having leptospirosis, a disease that 

 periodically reaches epidemic proportions in Cali- 

 fornia sea lions. The outbreak worsened in August 

 when 98 California sea lions were found sick or dead 

 along the California coast (compared to 35 in 1990 

 and 36 in 1989). Of these, 56 of 77 live animals 

 were diagnosed as having leptospirosis, and half of 

 those eventually died. The event continued into 

 September and October, when 39 and 23 cases were 

 diagnosed, respectively. In November and December, 

 the number of affected animals dropped to 7 and 1 . 



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