A rescued harp seal that seemed to be on the road to recovery suddenly took a sharp turn for the worse on Wednesday and had to be euthanized, the Marine Mammal Stranding Center said Thursday.

Harp seals and their pups are the subject of the second episode of Frozen Planet II, which is available now on iPlayer. One of the issues with climate change is that it’s really hard to see.

A 154-pound harp seal was hauled out of Brant Beach in Long Beach Island on March 8. In a post on Facebook, the MMSC said the seal’s behavior on the beach was observed for 24 hours by the ...