Deaths of Dolphins Elude Diagnosis

Deaths of Dolphins Elude Diagnosis

Bottlenose dolphins are dying and being washed ashore in the waters along the east coast, from New York to Virginia.  Federal wildlife officials say that a rapidly spreading infection could be attacking dolphin populations. But a specific diagnosis cannot be made for now.

In July, 89 dolphins were beached in three states, seven times the usual number.  A total of at least 124 of the cetaceans have washed onto beaches since July, all of them dead or dying. At least 64 have occurred off the coast of Virginia, 18 in New York waters and 26 in New Jersey. There are likely many more instances of victimized mammals at sea that are not detected, according to officials.

Similarly, in the region of Washington DC, an average of 64 bottlenose dolphins are found on or near shore in a year, on the Chesapeake Bay and in the Atlantic.  This year the Virginia Aquarium Stranding Response Team has been called to the scene of the stranding of 82 dolphins, 44 in the last month.  The monthly average is seven.

Maryland’s natural resources department has recorded 15 dolphin deaths this year, discovered on the shores of the bay and in the ocean. A one-day count of dolphins conducted annually by the National Aquarium and completed on July 12th of this year, showed that there were 113 dolphins off Maryland’s Atlantic coast.

Decomposition of many of the animals has not left Virginia aquatic animal specialists with much to go on.  This is similarly the case in the Baltimore area. Tissue samples from some of the more recent deaths have been sent for analysis.  But the results may be inconclusive.

However, tests on one dolphin carcass indicate that the cause of the deaths may be traced to morbillivirus, an infection that has been compared to canine distemper, based upon clinical signs and lesions in affected animals. It previously afflicted over 700 dolphins along the east coast from New Jersey to Florida over a 10-month period in 1987 and 1988. The morbillivirus contains agents that cause measles in humans, distemper in dogs and cats, and rinderpest (a contagious viral disease) in cattle.

But there are reports of other stranded dolphins suffering from pneumonia.  Officials said that it could take weeks to determine the cause—if ever.  Investigators never did find a cause in half of the 60 large-scale mortality events since 1991.

A cause of the dolphin deaths cannot be ascertained definitively.

This summer’s casualties come from only a portion of four discrete populations of dolphins.   20,000 of them live in separate southern and northern migratory groups near the east coast, 81,000 in the deep waters off the continental shelf, and about 785 in Pamlico Sound off the coast of North Carolina.

In the most recent strandings in the Virginia area, the deceased appear to be almost exclusively males of all ages and sizes.

According to the National Oceanic and Atmospheric Administration (NOAA), a bottlenose dolphin can range in weight from 300 to 1,400 pounds and normally lives for up to 40 to 50 years. They are protected under the Marine Mammal Protection Act of 1972.

The “unusual mortality event” may call for federal assistance in finding the cause. For now, the strandings and deaths are inexplicable.

By:  Tom Ukinski

Sources:    The New York Times

The Washington Post

PubMed.gov    Encyclopedia Britannica 

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