SAN JUAN, Puerto Rico - Five of 17 trained dolphins rescued during Hurricane Katrina and taken to a marine mammal center in the Bahamas are pregnant, officials said Thursday.

A sixth dolphin gave birth to a stillborn calf earlier this week, the Dolphin Cay center said in a statement.

The dolphins were from a Mississippi marine park that was destroyed by Hurricane Katrina. Some of the animals were swept out to the Gulf of Mexico following the storm. After being rescued, the dolphins were moved to a Bahamas' resort early last year.

The mammals had lived at Marine Life Oceanarium in Gulfport, Miss., doing jumps and other tricks for tourists, before it was severely damaged by Katrina.

The five pregnant dolphins -- two first time moms and three experienced mothers -- are doing well, said Teri Corbett, vice president of Marine Mammal Operations.

Corbett, in a phone interview, said the pregnancies were "a sign of adjustment."

"It means they're comfortable in their environment, and they're comfortable enough to raise children."

The dolphin that gave birth to a stillborn calf did not appear to experience complications during her pregnancy, officials said.

More than 50 percent of first-time dolphin births fail both in the wild and in controlled environments, said Dr. Michael Renner, a veterinarian who monitored the dolphin.

The dolphin center is located in the Atlantis Paradise Island resort. The rescued dolphins live along with four others in seven interconnected pools comprising an 11-acre lagoon at the resort.