A total of 129 dolphins have been found stranded in Cape Cod, Massachusetts, since early January.

Story highlights

"It's the largest single-species event" in the Northeast, a marine mammal expert says

Only 37 of 129 dolphins have survived to be released, says IFAW's Katie Moore

Necropsies have been done on nine animals; no cause has been determined

Some of the released animals have been tracked north of Cape Cod, where they belong

CNN  — 

The unexplained beachings of scores of dolphins over the past month along Cape Cod, Massachusetts, is the largest “single-species event” of its kind on record in the northeastern United States, a marine mammal specialist said Monday.

A total of 129 common dolphins have been found since the animals began stranding themselves in early January, said Katie Moore, marine mammal rescue and research manager for the International Fund for Animal Welfare.

Team members have been able to successfully release 37 of the 54 they were able to recover alive, but 75 others were dead or had to be euthanized on the spot, for a total of 92 dead, Moore told reporters in a conference call.

Specially equipped trailers have been used to treat and transport the living dolphins. The ones that are healthy enough are taken to the outer Cape Cod coast to be released.

Nine of the dolphins have been tagged with satellite tracking devices, Moore said, and most of the six that are still transmitting are north of Cape Cod, “where dolphins should be.”

While dolphin strandings are not uncommon on the cape, Moore said this event is extraordinary in its “protracted” nature as well as the number of dolphins involved.

“We’ve seen see an (annual) average of 228 strandings of dolphins and seals over the past 12 years” in the International Fund’s Northeast region, which spans from Virginia to Maine, Moore said.

“There is a large variability year to year,” she said, but this event represents “more than half my annual average in a month.”

Moore said the International Fund staffs a 24-hour hotline, and when they get reports “from beach-goers or anyone who finds an animal,” they alert one of their 300 trained volunteers and dispatch them to the scene. These responders are able to relay information about the dolphin’s species, sex and condition.

Once beached, a dolphin is vulnerable to predators and susceptible to organ damage and sunburn. If a dolphin is still alive, the responders get it onto its stomach, if it is not already, for easier breathing, keep away seagulls that would otherwise peck at it, and warm it with blankets or cool it with water as necessary, Moore said.

Necropsies have been performed on nine of the dolphins, and blood and microbial swab samples have been taken from some that were found alive, Moore said, but so far no pattern of disease or trauma has been found that would point to a cause.

Although the winter and early spring are the normal time of year for dolphin strandings to occur, the weather this season has been unusually warm, leading to speculation about climate change and subsequent “distribution of prey” as a possible causes.

Last week, Wellfleet harbormaster Michael Flanagan explained that usually, in the winter, “the harbor ices over and inhibits the animals from coming close to the shore. But now that the water is warmer, we’re seeing lots more dolphins washing up than ever before.”

However, the International Fund’s Moore cautioned, while climate or other external factors such as acoustic disorientation can’t be ruled out, “we don’t have a single answer.”

“As time goes on we can put more of the pieces of the puzzle together,” she said. “The sad fact in these events is that we often never come up with that answer, and that is incredibly frustrating.”

She did, however cite the nature of the dolphins and the geology of Cape Cod as two contributing factors in these events, historically:

“Common dolphins are incredibly social animals and form bonds to forage for food and avoid predators,” she explained. Those bonds, while they serve the animals greatly in the open ocean they’re accustomed to, can be devastating when the creatures are brought in contact with Cape Cod’s gently sloping shallows and convoluted estuaries, which are “very foreign to these species.”

Moore said the event, because of its scale and duration, is taking “a huge toll” on the resources of the animal rescue and advocacy group, financially and physically.

“This is very hard labor. These animals can weigh 200 or 300 pounds each,” she said.

The organization, which gets its funding through donations and grants, has a base operating budget of less than $300,000, and she estimated this event has coast “at least 50 or 60 thousand dollars,” not including staff time.

CNN’s Cameron Tankersley and Kendall Green contributed to this report.