Work continues on solving dolphin deaths

The number of dead or dying dolphins that have washed ashore recently on the New Jersey coast increased to 28 Tuesday morning with the discovery of a "skeletonized" carcass at Holgate.

Strandings also are continuing along the coast, from New York to Virginia.

In July alone, 91 bottlenose dolphins became stranded along this stretch of coast, "a very significant increase over the norm," said Mendy Garron, who oversees a regional stranding network for the National Oceanic and Atmospheric Administration.

A team of veterinarians, virologists, toxicologists, and other experts is reviewing the data to determine whether the strandings rank as an "unusual mortality event" - a formal designation that would loosen funds for an intensive investigation led by federal authorities.

Based on necropsies - the animal version of autopsies - at the University of Pennsylvania's New Bolton Center in Kennett Square, officials know that four of New Jersey's stranded dolphins had pneumonia. One had morbillivirus, an infection related to human measles and canine distemper that has figured in past strandings.

But pinpointing an overall cause or causes for the strandings could take weeks or months, Garron said.

July's strandings of bottlenose dolphins numbered 47 in Virginia, seven in Maryland, two in Delaware, 20 in New Jersey, and 15 in New York.

Since 1991, officials have declared 59 "unusual mortality events." Causes include ecological factors, infectious diseases, biotoxins, and human interaction, but many remain undetermined.

The species most commonly involved are California sea lions, manatees, and bottlenose dolphins.

One official mortality event involves the stranding of emaciated dolphins this summer in the Indian River lagoon system along the east coast of Florida. By the end of July, 53 dolphins had been found.

Another event being investigated is in the northern Gulf of Mexico, where more than 1,000 dolphins and other related species - all referred to as cetaceans - have been reported dead or dying since the Deepwater Horizon oil spill.

Garron said it is important to study these because dolphins are "sentinels for water quality and life in our oceans. Plus, when something is affecting these animals, it could be affecting us as humans."

New Jersey environmental officials have said the current strandings appear to be part of "a natural disease cycle" and not water quality.

Nevertheless, "these animals can carry diseases that can be transmissible to other animals, other mammals, or even humans," Garron said. "It's something we're continuously screening them for. The more we look, the more we tend to find."

In 2011, officials declared an unusual mortality event for harbor seals in New England, traced to an avian-based influenza. The strain was not transmissible to humans, but in the process of discovering that, scientists learned how the virus mutated over several months.

Studies after a 1987-88 die-off of bottlenose dolphins along the East Coast, in which 742 animals died, showed there were distinct dolphin populations along the coast, said Lance Garrison, a NOAA research fishery biologist based in Florida.

They congregate in the same areas and breed among themselves.

Satellite tagging data and other studies show that the dolphins stranding along the New Jersey coast are likely part of a population that summers there, then migrates to near Cape Hatteras, N.C., for the winter.

They stay mostly along the coast and out to water depths of about 80 feet, Garrison said.

Scientists' best estimate is that the population numbers nearly 10,000. But in a year, they can withstand only about 70 cases of "human-caused mortality" - which could include strandings, depending on the cause - and still be considered a healthy population, he said.

The current number of strandings is higher, but the animals that came ashore in Virginia could be from a more southerly group of dolphins.

A third population stays farther offshore. Garrison said genetic tests could distinguish between coastal and offshore animals, but not between the northern and southern groups.

If most of the strandings turn out to be from the northern group, "it would be reasonable for that to have a significant effect on the population long-term," Garrison said.

As the carcass count mounts, scientists at New Bolton and other places able to handle large animals continue with the necropsies.

In a process that takes upward of an hour, they begin with an overall assessment of the organs and tissues, said Perry Habecker, chief of large-animal pathology, then begin analyzing tissue samples under a microscope to search for evidence of cancer, infections, or other systemic diseases.

Officials warn the public not to touch stranded animals but to call the marine mammal stranding network (1-866-755-6622 in the Northeastern United States).