Savannah State researchers document Tybee Island dolphin birth, attempted infanticide

Savannah State researchers have laid claim to the first documented live birth of a wild bottlenose dolphin.

But the birth was only the beginning of a remarkable chain of events. As the researchers watched the dolphin baby born just off Tybee Island, they quickly realized something else was going on.

"More surprisingly, we also witnessed what we believe to be an infanticide attempt on the newborn calf by two male dolphins just minutes after the birth," said Robin Perrtree, a marine sciences technician at Savannah State University.

Perrtree and her colleagues published their observations in the journal Marine Mammal Science last week. The birth and attempted killing of the newborn dolphin occurred in August 2013 at the mouth of the Savannah River on the north end of Tybee, where the local researchers were working on a collaborative study with Woods Hole Oceanographic Institute. It was only Perrtree's second day on the water in her then-new position managing SSU's Dolphin Sciences Lab. 

"We approached a group of dolphins, then suddenly noticed a very small calf with them and a pool of red in the water," Perrtree said.

Photographs show the umbilical cord still attached to the mother, and the baby's dorsal fin pushed flat by the tight space of the womb.

"We started recording them as we realized that we had just witnessed a birth, when suddenly a couple of additional animals joined the group and started submerging the calf," Perrtree said.

That behavior continued as the researchers observed, photographed and shot video.

"Aggressive behaviors were apparently being directed at the newborn calf, including what appeared to be forcible submergence of the neonate by the presumed male pair during at least four bouts over a 23 minute period," they write in Marine Mammal Science.

A male pair, or alliance, is a well-known social unit in dolphin populations, Perrtree said. The only other bond as strong is that of a mother and calf, which stay together three to five years. Two males typically pair off as they reach maturity.

"They stick together for the rest of their lives," Perrtree said. "They work together and protect each other from sharks and such by having that additional awareness."

Male pairs also work together to isolate females and increase their chances of mating with them. Killing a calf can be part of that strategy because it cuts short the typical two- to three-year period when a female with a nursing calf doesn't mate.

"If the calf does not survive she's back in estrus in a matter of a few months," Perrtree said.

The attack may not have been entirely spontaneous. The researchers had spotted this male pair near the mother dolphin about 90 minutes before the birth, "possibly indicating they were tracking the birth in preparation for the infanticide attempt," they wrote.

Dolphin infanticides have been reported before, but typically with older babies.

"I don't think anyone expected the apparent infanticide attempt to happen minutes after birth - all other ones seen in marine mammals have happened days to weeks after birth," Perrtree said.

Previous reports had documented a different type of attack as well, with the babies flipped or tossed into the air.

Perrtree and her colleagues knew it was rare to witness a dolphin birth, but were unaware at the time that it had not been described in the scientific literature. Still, mindful of the opportunity at hand, they deployed a hydrophone into the water to record the dolphins' vocalizations. The result was another rarity: The researchers are able to associate the low frequency tonal sounds they recorded with the aggressive behavior they saw. The same sounds continued after the scientists backed off too far to see what was happening.

"Having these recordings from a known aggressive context will provide insights to other recordings when we don't know what the animals are doing," said Laela Sayigh, co-author and research specialist at Woods Hole Oceanographic Institute in Massachusetts.

The attempted infanticide is a reminder that dolphins are wild animals, Perrtree said. It's a lesson particularly worth noting on the Georgia coast where human and dolphin interactions are believed to be more frequent than anywhere else, as noted in a previous study from Savannah State researchers. 

These interactions are potentially harmful to both humans - because of dolphin bites, which can cause infection or carry diseases - as well as to the dolphins, Perrtree said.

"Dolphins that are attracted to humans and boats are at risk of injury from propellers, fishing gear entanglement - recreational gear as well as crab-pot gear and shrimp trawls - and shark bites. Sharks are also attracted to bait and discarded bycatch," she said.

"In addition, these animals may be ingesting inappropriate food or spoiled fish (as is often the case with bait). Unfortunately calves are the most susceptible to injury and entanglement."

The fate of this particular newborn is unknown. It survived at least until the next day when researchers again spotted it along with its mother and the two presumed attackers. But they have not been seen again.

Along with Perrtree and Sayigh, the study authors were Allison Williford, Mary Carla Curran and Tara M. Cox of SSU; and Alessandro Bocconcelli of Woods Hole.

Note: The photos accompanying this article were collected in accordance with the U.S. Marine Mammal Protection Act on Aug. 23, 2013 by Robin Perrtree under NMFS LOC #14219 issued to Dr. Tara Cox.

ON THE WEB

Go towww.savannahnow.com to see video footage of the presumed attack on the newborn dolphin.

Go to

http://onlinelibrary.wiley.com/doi/10.1111/mms.12248/abstract to read the journal article.