MARINE MAMMAL COMMISSION — Annual Report for 1992 
movement patterns of bottlenose dolphins in the area. 
As noted in Chapter X, the Commission provided 
funds to purchase radiotags to enhance this effort. 
The fact that most animals appeared to have died 
in a very short period of time suggested that the 
deaths may have been due to an extremely virulent 
disease or a toxic substance. Traces of aldicarb, an 
insecticide commonly used in the area to prevent 
insect infestation of sorghum and cotton, were found 
in several of the water samples collected during the 
investigation. Aldicarb is highly toxic to mammals. 
Although no traces of the chemical were found in any 
of the dolphins or other animals found dead in the 
area, such chemicals cannot be detected in badly 
decomposed animals. Thus, failure to find evidence 
of the chemical in the tissue samples does not rule out 
the possibility that aldicarb was responsible or contrib- 
uted to the deaths. No indications of naturally occur- 
ring biotoxins, diseases, or potentially harmful levels 
of other contaminants were found. 
The investigation is not expected to be completed 
until sometime in 1993. The Commission, in con- 
sultation with its Committee of Scientific Advisors, 
will review the results of the investigation and advise 
the National Marine Fisheries Service, the Environ- 
mental Protection Agency, the Department of Agricul- 
ture, and other appropriate agencies of follow-up 
actions needed to assess and avoid future mortalities 
of this type. 
Sea Lions and Other Pinnipeds in California 
In late May 1992 more than 1,500 seals, mostly 
juvenile California sea lions, began hauling out and 
dying on beaches in California. Most of the animals 
were emaciated and lethargic, suggesting that they 
were dying of starvation. 
The unusual occurrence coincided with an El Nifio 
— a meteorological and oceanographic phenomenon 
that occurs at irregular intervals in the eastern tropical 
Pacific and which is characterized by warming of 
surface waters. When a similar but stronger El Nifio 
event occurred in 1982-1983, many pinnipeds died 
due to starvation. There were no indications, in either 
case, of unusual diseases, biotoxins, or unusually high 
levels of environmental contaminants. Thus, it 
146 
appears that warming of surface waters altered the 
distribution or abundance of prey species to such an 
extent that the affected pinnipeds were unable to find 
sufficient food. 
[For information on the effects of El Nifio events 
on pinnipeds, see Trillmich, F., and K. A. Ono (Eds). 
1991. Pinnipeds and El Nifio: Responses to Environ- 
mental Stress. Ecological Studies 88. Springer- 
Verlag, New York, Berlin, Heidelberg. 291 pp.] 
Harbor Seals in Oregon and Washington 
On 4 October 1992 biologists working on the 
Columbia River found 13 harbor seals, three harbor 
porpoise, and one rough-toothed dolphin dead on 
beaches near Astoria, Washington. Other nearby 
beaches were searched on 5-7 October and 14 addi- 
tional harbor seals and one harbor porpoise were 
found. 
The National Marine Fisheries Service recovered 
most of the animals, conducted necropsies, and 
collected tissue samples. Seventeen of the 18 harbor 
seals recovered had bleeding from the nares, moderate 
to extensive hematoma in cervical and thoracic muscu- 
lature and internal organs, and extensive pooling of 
blood in the thoracic and abdominal cavities. Two of 
the animals also had punctures in the abdomen that 
appeared to be gunshot wounds. No evidence of 
biotoxins or unusual concentrations of heavy metals or 
organochlorine compounds were found. 
None of the porpoises showed signs of trauma. 
The findings suggest that the harbor seal and porpoise 
mortalities were unrelated. The tissue damage and 
bleeding found in the harbor seals was consistent with 
concussion trauma caused by underwater explosions. 
Phocine Distemper Virus in U.S. Waters 
The death of more than 17,000 harbor seals in the 
North Sea in 1988 was attributed to a morbillivirus. 
The virus is similar to but not the same as the morbil- 
livirus that causes distemper in dogs. 
In December 1991 the New England Aquarium 
reported to the National Marine Fisheries Service that 
