MARINE MAMMAL COMMISSION - Annual Report for 1998 



At least two of the unusual events listed above 

 were caused by natural toxins. Humpback whales in 

 Cape Cod Bay (Massachusetts) died after ingesting 

 mackerel containing saxitoxin, a neurotoxin produced 

 by the dinoflagellate that causes paralytic shellfish 

 poisoning in humans. The deaths of Florida manatees 

 in 1996 resulted from exposure to brevetoxin, a toxin 

 produced by the red tide organism Gymnodinium 

 breve. Toxic algal blooms appear to be occurring 

 more frequently in many parts of the world, perhaps 

 spurred by pollution and other environmental changes. 



Unusual Mortality Events in 1998 



Relatively few events involving unusually high 

 levels of marine mammal mortality occurred during 

 1998. As discussed below, however, events were 

 recorded for New Zealand sea lions in the Auckland 

 Islands, California sea lions in central California, 

 pinniped species along the California coast, and 

 beaked whales along the southeastern U.S. coast. 



New Zealand Sea Lions 



The most serious event in 1998 involved New 

 Zealand (Hooker's) sea lions, a species numbering 

 some 12,(X)0 to 14,000 animals that is restricted to the 

 Auckland Islands south of New Zealand. More than 

 1 ,600 pups and an unknown number of adults died 

 between mid- January and early February 1998. A 

 scientific team from the Massey University Cetacean 

 Investigation Centre and the New Zealand Department 

 of Conservation conducted an investigation. Sample 

 collection and transport were hampered by the site's 

 remote location and severe weather, but tissue and 

 blood samples were collected opportunistically — 

 mostly from animals examined in the later stages of 

 the event. Preliminary results of the investigation 

 failed to confirm a cause for the die-off. Studies 

 revealed neither consistent lesions nor pathogenic 

 agents known to cause epidemics among marine 

 mammals. Investigators concluded that the event may 

 have been caused by a natural toxin acting alone or in 

 combination with opportunistic pathogens and perhaps 

 El Niiio-related alterations in prey availability. Al- 

 though no biotoxins were detected in tissues, concur- 

 rent toxic algal blooms at other sites around the New 



Zealand mainland caused clinical illness in humans 

 and were considered the likely cause of death of 

 fishes, seabirds, and other pinnipeds in affected areas. 



California Sea Lions 



More than 70 adult and subadult California sea 

 lions in physical distress were recovered from central 

 California beaches in May 1998. Symptoms included 

 seizures, loss of coordination, and vomiting; most 

 animals were in good body condition. More than half 

 of the sea lions died or were euthanized; some survi- 

 vors appeared to recover quickly, but others required 

 intensive medical care and prolonged rehabilitation. 

 The cause of the event was thought to be domoic acid, 

 a toxin produced by the diatom Pseudo-nitzschia 

 australis. Evidence to support this conclusion includ- 

 ed a coincident algal bloom involving a number of 

 species oi Pseudo-nitzschia, with cell counts reaching 

 200,000 per liter in Monterey Bay; symptoms indica- 

 tive of a neurological disorder; high levels of domoic 

 acid in prey species; bird kills in the affected area; 

 lesions consistent with domoic acid poisoning; and 

 detection of the toxin in serum samples. 



Other Pinnipeds Off California 



Unusual numbers of pinniped deaths and strandings 

 along the California coast, as in other areas of the 

 eastern Pacific Ocean, continued through the winter of 

 1997-1998 in conjunction with the strongest El Nifio 

 on record. As in previous events, the greatest impacts 

 were on pup production and first-year survival. In 

 late 1997 the numbers of dead or stranded northern 

 fur seals and California sea lions found along the 

 California coast rose dramatically as El Nifio condi- 

 tions continued to develop; the number of weaned 

 northern fur seal pups stranded along the central and 

 northern coast of California during October and 

 November 1997 was at least four times the normal 

 number for that time of year. On San Miguel Island, 

 about 1,500 northern fur seal pups — or 75 percent of 

 the cohort — died before weaning. Mortality of 

 northern elephant seal pups at the Point Reyes colony 

 in late February 1998 approached 90 percent after 

 pups and adults were washed off beaches in a series 

 of El Nino-related storms. 



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