PUERTO MADRYN — Were they sick? Were they chased ashore by hungry orcas? Those are two of the theories scientists are considering following the discovery this week of nearly 70 beached dolphins — many of them already dead — near Puerto Madryn in central Argentina's Chubut province.

For now, though, the dolphin deaths are still very much a mystery. "We don't know for certain what caused this dolphin stranding," Mariano Coscarella, a researcher at the government scientific agency CENPAT told Clarín. "We don't have enough clues to really clarify the matter yet."

Coscarella said that he and his colleagues counted 68 common dolphins in total. Together they managed to return 19 to the water. The rest died. The CENPAT researcher also said the animals appeared intact. Adding to the mystery is that this is the first such mass stranding ever recorded in the Golfo Nuevo, as the water around Puerto Madryn is known.

The scientists plan to perform necropsies on the corpses. Hopefully that'll provide additional clues. One of Coscarella's CENPAT colleagues, Silvana Dans, isn't ruling out the possibility that the dolphins were "corralled" by killer whales and thus pushed off course — and ultimately onshore.

"We know from other cases studied that there could have been a pursuit by orcas," said Dans. "The dolphins could have felt trapped." Another hypothesis, given that the dead dolphins are part of a single group is that they were victims of "some kind of epidemic," she added.

The CENPAT researchers were also surprised to find such a large batch of common dolphins. "That's unusual here," said Dans, who explained that the more prevalent species in the area is the dusky dolphin.

Whatever the cause, the scientists will have to be patient. The necropsies and other tests are expected to take several weeks.