Perplexing Spike in Bottlenose Dolphin Deaths Hits U.S. East Coast

2016-06-28T19:37:38+00:00 August 8, 2013|
The Virginia Aquarium’s Stranding Response Program team members retrieve a dolphin from the beach. (Virginia Aquarium)

(Click to enlarge) The Virginia Aquarium’s Stranding Response Program team members retrieve a dolphin from the beach. (Virginia Aquarium)

Since the beginning of July, more than 100 dolphins have washed up dead along the U.S. East Coast, from New York to Virginia. No one knows why, or whether the deaths are connected.

(From Wired / by Nadia Drake) — The number is a noticeable spike in mortality, about seven times the average for the last two Julys, according to stranding data collected by NOAA’s Marine Mammal Stranding Program. “It could take several months, if not longer, to determine what could be behind this,” said Maggie Mooney-Seus, spokeperson for NOAA’s Northeast Fisheries Science Center.

In June, rescue centers in New Jersey and Virginia started recording higher than normal numbers of dead bottlenose dolphins (Tursiops truncatus). By July, the mortalities had shot up even more, and centers in New York and Maryland were also reporting unusually high totals.

“They’ve all been found dead on the beach, or near death,” said Joan Barns, with the Virginia Aquarium, the institution in charge of handling the state’s strandings.

Dolphin deaths in July for the past three years. (Source: NOAA)

(Click to enlarge) Dolphin deaths in July for the past three years. (Source: NOAA)

The tally has scientists concerned: The last time such elevated death rates were seen was in 1987, when the toll climbed much higher. Between June and May, 1988, more than 750 dolphins died, washing up along shores from New Jersey to Florida. It took scientists three years to sort out what was going on, and in the end, they determined that the dolphins had succumbed to a morbillivirus – a previously unknown pathogen that causes a measles-like disease in marine mammals.

Since the beginning of this year, rescue groups in Virginia have retrieved the carcasses of more than 100 dolphins, 47 in July alone.  Most of the animals have been found in the southern Chesapeake Bay, rather than on the state’s ocean-facing shores.

Virginia Aquarium’s Stranding Response Program team members attend to a dolphin on the beach. (Virginia Aquarium)

(Click to enlarge) Virginia Aquarium’s Stranding Response Program team members attend to a dolphin on the beach. (Virginia Aquarium)

Farther north, 35 dolphins were found in July along the New Jersey and New York coasts, two in Delaware, and seven in Maryland. And across the region, 28 more have died so far in August. Preliminary necropsy results suggest that four of New Jersey’s dolphins had pneumonia, and one had morbillivirus — hardly a sweeping trend. Scientists and rescue centers are still analyzing tissues from the animals collected, and will be looking for anything that could explain why they’re dying. Teams are also going to be looking at the animals’ genetic sequences to find out if they’re coming from the same populations.

NOAA is now in the process of deciding whether the deaths meet the criteria for an Unusual Mortality Event, a designation made when a higher-than-normal number of marine mammals are dying unexpectedly, and the deaths merit immediate attention. Once a UME has been declared, federal funds and investigators are sent to help out the regional teams already on the ground.

In the south, a dolphin die-off in Florida’s Indian River Lagoon just earned that same designation, though the events probably aren’t related. Dolphins and marine mammals strand for a number of reasons, including changes in oceanographic conditions, warming water, toxin exposure, malnutrition, and disease.