Conservationists counted 615 dead dolphins along a 90-mile stretch of beaches in Peru, a wildlife group said Wednesday, and the leading suspect is acoustic testing offshore by oil companies.

"If you can count 615 dead dolphins, you can be sure there are a great many more out at sea and the total will reach into the thousands," Hardy Jones, head of the conservation group BlueVoice.org, said in a statement after he and an expert with ORCA Peru walked the beaches.

Indeed, the head of a local fishermen's association told Peru21.pe that he estimated more than 3,000 dolphins had died so far this year, based on what he saw in the water and on beaches.

BlueVoice.org stated that "initial tests ... show evidence of acoustical impact from sonic blasts used in exploration for oil."

The ORCA Peru expert, veterinarian Carlos Yaipen Llanos, said that while "we have no definitive evidence," he suspects acoustic testing created a "marine bubble" -- in essence a sonic blast that led to internal bleeding, loss of equilibrium and disorientation.

Another possibility is that the dolphins suffered from a disease outbreak, Yaipen Llanos said.

"It is a horrifying thought that these dolphins would die in agony over a prolonged period if they were impacted by sonic blast," said Jones.

Numerous dolphins first started washing ashore in January, with the largest amount coming in early February. Thousands of dead anchovies were also seen.

BlueVoice.org noted that the U.S. has suspended similar testing in the Gulf of Mexico due to recent sightings of dead and sick dolphins. The ban was set to last through the dolphins' calving season, which ends in May.