Chapter VI 
MARINE MAMMAL STRANDINGS AND DIE-OFFS 
Since the late 1970s there appears to have 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, sea lions in California, 
manatees in Florida, bottlenose dolphins in Texas, and 
humpback whales in Cape Cod, Massachusetts. 
Among the largest and most publicized were the 
deaths of more than 700 bottlenose dolphins along the 
U.S. mid-Atlantic coast in 1987-1988, more than 
17,000 harbor seals in the North Sea later in 1988, 
and more than 1,000 striped dolphins in the Mediter- 
ranean Sea in 1990-1991. 
Unusual Mortality Events in 1992 
In 1992 the unusual marine mammal mortality 
events described below occurred in U.S. waters. 
Also, evidence of phocine distemper, the cause of the 
large harbor seal die-off in the North Sea in 1988, 
was found for the first time in seals in U.S. waters. 
Bottlenose Dolphins in Texas 
In March 1992, 59 bottlenose dolphins washed up 
on beaches in Aransas and Calhoun Counties, Texas, 
and were recovered dead. Of these, 46 washed up in 
an eight-day period between 16 and 24 March. 
The Texas Marine Mammal Stranding Network 
advised the National Marine Fisheries Service early in 
April that stranding levels in the two counties were 
much higher than previous averages for that time of 
year. The Service initiated an on-site investigation on 
12 April. In addition, the Service consulted the Task 
Force on Unusual Marine Mammal Mortalities for 
advice on what should be done to determine the 
magnitude and cause of the event. This task force had 
145 
been constituted by the Service during the investiga- 
tion of the unusually high numbers of bottlenose 
dolphin mortalities that occurred in the northern Gulf 
of Mexico from January through June 1990. 
Members of the task force met with representatives 
of the Service and the Marine Mammal Commission 
during the Commission’s meeting in Tallahassee, 
Florida, on 30 April-2 May 1992 to review the 
ongoing investigation. During the review it was noted 
that water, sediment, and fish samples had been 
collected in areas near where the dead dolphins were 
being found and that surveys were being conducted to 
look for both live and dead dolphins in nearby areas. 
It also was noted that all of the dolphin carcasses that 
had been found were badly decomposed, suggesting 
that they had died at least several days before they 
were found. In addition, it was noted that on 14 
April numerous dead fish (primarily black drum and 
catfish), along with five bottlenose dolphins and a 
number of seabirds, had been found on Sand Point in 
Lavaca Bay. These, too, were badly decomposed or 
had been eaten by scavengers to the extent that few 
useful tissue samples could be collected for disease 
and contaminant analyses. 
The task force endorsed the various components of 
the investigation initiated by the Service. It also 
recommended that a number of live animals be 
captured and that blood and other tissue samples be 
collected from these animals to determine if they had 
diseases or contaminant levels that might explain the 
unusually high mortality. In response, the National 
Marine Fisheries Service made arrangements to 
locate, capture, and collect samples from up to 50 
bottlenose dolphins in and near the two-county area. 
The Service subsequently captured and released 38 
dolphins in July. An extensive set of samples was 
collected from each animal. Analyses of the samples 
had not yet been completed as of the end of 1992. 
The Service also funded a study to determine the 
