A seven-month-old Hawaiian monk seal — rescued after his mother abandoned him less than one day after he was born on Kaua'i — is thriving as it adjusts to the wild.

The Coast Guard last week took the seal, which now weighs 150 pounds, by helicopter to a secret location in the main Hawaiian Islands, where other monk seals live.

When scientists brought him to the water's edge and opened the cage, the pup immediately took off into the water and didn't look back.

It has so far successfully adapted to the wild, said David Schofield, marine mammal response coordinator for the National Marine Fisheries Service.

"Thinking back on how small and scrawny that little seal was, a little bag of bones, and then seeing it fat and healthy and on its way out to the wild, it's just the best feeling in the world," Schofield said Tuesday.

Hawaiian monk seals are an endangered species. Only about 1,100 to 1,200 exist and their population is declining about 4 percent each year.

Many seals are being killed by sharks, while others are starving because they can't find enough food. The poor state of the species made rescuing the emaciated pup all the more important for biologists.

When National Oceanic and Atmospheric Administration officials found the pup, he was trying to suckle a rock.

"One of the saddest things I've seen in the 20 years I've been working with marine mammals is to see this little black monk seal pup with its little flippers stretched out with this large rock and trying to nurse from it," Schofield said.

The scientists tried to reintroduce the pup to his mother, but the female seal barked at him and seemed more interested in an adult male seal.

The mother had abandoned another pup at the same location on Kaua'i last year. By the time that pup was found, it was suffering and had to be euthanized.

The recovery team determined the new pup, if left alone, would have no chance of surviving. So they brought him to O'ahu to nurse him to health.

The following days were the most critical for the 30-pound pup. Biologists knew there was a great chance the pup could die, because people had never successfully cared for a monk seal that young.

Dr. Gregg Levine, the pup's chief veterinarian, said the most important thing at first was finding the right nutritious food formula since the pup didn't nurse from its mother at all.

In August, when the pup was 3 months old, scientists felt it was ready to be introduced in the wild again and moved it to an ocean pen at Marine Corps Base Hawaii in Kane'ohe Bay.

There, the pup learned how to eat on its own, catching live octopus, fish and crabs.

Levine and Schofield say it's difficult to predict the pup's chances of survival.

The real test is seeing if the pup makes it to sexual maturity, which typically occurs when it is 5 to 7 years old.

Schofield said scientists have learned valuable lessons from this monk seal that can be used to help this endangered species.

"We're very happy for the individual," Schofield said. "If this population continues to decline at the rate that it is, efforts like this (are) going to be necessary to recover the species."