Dennis, the stranded manatee rescued on Saturday morning from Sesuit Harbor near Dennis, Massachusetts, died Sunday with just one hour before he reached SeaWorld in Florida.

Dennis died about 3 p.m. after having endured a 27-hour trip to Orlando, officials from the International Fund for Animal Welfare (IFAW) said.

“We hear the animal had done well during the transport and quietly stopped breathing this afternoon. We thought the animal was going to make it, and when we heard it didn’t, it was tough,” Katie Touhey, the emergency release manager for marine mammals, strandings and entanglements at the IFAW, said. “I can't help but feel sad when an animal dies after so much effort trying to save him. Nature does what it is going to do, and that's just part of reality,” she added.

The exact cause of deaths is not known yet, but Dennis was hypoglycemic and had a low body temperature, about 23 degrees below normal when he was captured. He was immediately administered a treatment which raised his body temperature from 73 degrees to about 89 degrees Fahrenheit. A manatee's normal body temperature is usually in the low 90s. However, it seems the treatment did not help Dennis. A necropsy is to be performed later this week to reveal the exact cause of the death. If Dennis had survived , he would have been the first manatee found so far north to be rescued successfully, A.J. Cady, director for the International Fund for Animal Welfare said.

This type of marine mammal, which usually lives off Florida and the southeastern coast of the US, isn’t accustomed to living in chilly waters. If a manatee is too cold, it stops eating and eventually dies.