The aquarium has yet to resume its popular dolphin shows because the surviving dolphins remain distressed by the deaths.
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"The only thing they had in common was that they were both born to first-time moms," Whitaker said. "We're still in the mode of trying to understand everything that happened and what we can do differently."
The Johns Hopkins Department of Molecular and Comparative Pathobiology performed the necropsy, the animal equivalent of an autopsy.
The unnamed calves died one after the other last month.
The babies, one female, one male, were born in April to Maya and Spirit, half-sisters who are both 10 years old and first-time mothers. Spirit's calf arrived on the morning of April 14. Maya's was born two weeks later.
Maya's calf, the male, died first — he was found dead in the pool when aquarium staff arrived at work on June 21. The cause was ruled respiratory infection or an inflammation of the lungs. Bacteria, a virus or even another factor might have caused the infection, Whitaker said.
Maya had trouble nursing the calf immediately after the birth — a situation that lasted three days. Whitaker suspects that those early, critical days without enough milk might have left the calf vulnerable and without certain immunities.
"If a calf isn't nursing within six hours, I'm starting to worry," he said. "By three days, you're hoping things are going to turn out OK."
Spirit's calf died four days after the first in the arms of aquarium staff as they tried to save her. Internal bleeding was ruled the cause. Though Whitaker said the most likely cause of such bleeding would be an injury, he said aquarium staff aren't sure how the calf was hurt — though a belly blow from the mother wouldn't be uncommon.
It's also possible, he said, that the calf had a blood-clotting disorder or an autoimmune disease.
"We will follow up to try to see if we can learn what ultimately caused it," Whitaker said. "We may never know in the end."
Both in the wild and in captivity, mortality rates for dolphin newborns are high — about 33 percent. Even fewer calves born to first-time mothers survive, Whitaker said.
Though the dolphin trainers assumed that they would be able to resume shows a few days after the second calf's death, when they attempted to do so, they saw warning signs that the surviving dolphins were still traumatized.
The dolphins haven't performed since the end of June — the longest time the Inner Harbor attraction has been without the show.
"When something like this happens, the other animals get upset. The moms are upset. It creates a stress on the colony," Whitaker said. "Right now we're watching the animals and letting them have every opportunity to do what they need to do to recover as a social group."
When they attempted to resume performances last month, Nani, the 500-pound matriarch of group, refused to eat. Other dolphins take their cues from Nani, so trainers knew that if she didn't want to perform, the others wouldn't either.
"She's our rock-solid animal," Whitaker said. "If she doesn't want to eat and pay attention, that gives us great pause. "
So trainers stopped the shows to give the dolphins time to rest and recover. Staff, emotionally spent after losing the calves, needed time, too.
Instead of the usual dolphin shows, the aquarium has allowed visitors to enter the dolphin area for free to spend as much time as they want watching the animals swim, eat and train. Some visitors enjoyed the more relaxed opportunity to observe the dolphins, but Whitaker said others complained about missing the show they had expected.
Trainers plan to begin trying to restart shows next week, if the dolphins seem up to it — but the performances won't be scheduled, and they'll be free. It's unclear when official, ticketed shows will resume — Whitaker hopes by the end of the summer.
"We're going to see how it goes with the animals," he said. "If they're telling us for any reason they don't want to, we're going to take a step back. Our commitment is to the health of the animals. That comes first, before shows."