The two seals were part of a group of four adult harbor seals coming from the Storybook Gardens in London, Ontario, Friday to join 11 other seals in the Sea Lion Sound exhibit at the St. Louis Zoo, the St. Louis Post-Dispatch reported.
Steve Bircher, curator of mammals at the St. Louis Zoo, said the animals were doing fine as they went through U.S. Customs and the U.S. Department of Agriculture and U.S. Fish and Wildlife Service inspections. They also appeared healthy during frequent checks on the way to St. Louis.
But then, about 4 p.m. Friday, Bircher said one of the seals was not responsive and was taken to the nearest zoo -- the Fort Wayne Children's Zoo in Indiana -- where it was pronounced dead. Another seal was showing signs of distress while at the Fort Wayne zoo and then also died.
A third seal began showing similar symptoms, but stabilized after treatment. That seal began to show some behavioral changes after the team began moving toward St. Louis again Saturday and was left at the Indianapolis Zoo, which was along the route.
The fourth seal arrived in St. Louis Saturday afternoon and appeared to be healthy, Bircher said.
The zoo's veterinary pathologist will conduct a full necropsy on both animals. Determining a cause of death could take several weeks.
Notable deaths of 2014 [PHOTOS]