Most harbor seals live for around 25 to 35 years. Female harbor seals tend to live longer on average than male seals. However, estimates for seal life spans in captivity and the wild often differ due to the lack of predators in zoos and aquariums.
Some estimates for harbor seal life spans are lower, with averages of 15 years in the wild and 20 or more in captivity. Certain harbor seals in captivity (usually female seals, who often live five to 10 years longer than male seals) have lived to be 40 or even older. Gray seals in European aquariums have been known, very rarely, to survive into their 50s.