Why did six dolphins die and wash up along the Jersey Shore over the past week? Officials are using science to unravel the mystery.

The first dolphin was found July 18 at Long Beach Township and two more were discovered Monday in Holgate and Barnegat Light.

Another two turned up Wednesday in Holgate and Ocean City, and the last washed up Thursday at Ship Bottom.

The causes of the deaths will not be known until officials have the results of necropsies, said Bob Schoelkopf, founding director of the Marine Mammal Stranding Center in Brigantine. That information is expected to begin coming in Monday.

"Every year we have dolphin deaths," Schoelkopf said. "We won't speculate on a cause until the lab results come back."

Schoelkopf said that sending the dolphins for necropsies is normal any time large marine animals are found.

Though dolphin and other marine animal deaths are not uncommon, experts say it is unusual for so many to wash up in such a short time.

"If it continues like this, we'll definitely investigate more," said Mendy Garron, a regional marine-mammal stranding coordinator with the National Oceanic and Atmospheric Administration.

If the dolphins died of disease, a pathologist can study tissue samples and determine whether the disease was viral or bacterial. "It's a very tiered approach," Garron said.

The postmortem examination is just one part of an investigation that can uncover other trends, Garron said.

This year, officials have found an increase in the number of animals off New York and New Jersey, which could affect prey distribution in the ocean.

"It's like piecing a puzzle together in many ways," Garron said.

Each dolphin was sent to the University of Pennsylvania's New Bolton Center in Chester County for examination.