At around 100 tons, the Bowhead Whale is the second largest animal on Earth.
Living their entire life in nutrient rich arctic seas, their only real threat comes from humans. Though Orca's are known to predate on them, instances seem to be few and far between.
In 2007 an individual caught off the coast of Alaska was found to have a failed exploding harpoon tip embedded in its blubber of a type made in 1890. So this individual at just 50 tons was over a hundred years old. The Inupiat people are allowed to kill a limited number of Bowheads each year for food and oil and during a survey by the International Whaling Commission on their kill in the 1970's, 80's and 90's a number of whales were found to have stone harpoon tips embedded in their blubber. These harpoon tips have not been used since the 1860's.
Tissue samples from these Bowheads were examined by a team from the Scripps Institution of Oceanography who used amino acid racemization techniques to establish the age of these whales. Five were found to be over 100 yrs old and one nearly 200 yrs old. Further testing at the University of Washington put the oldest whale at 211 yrs old.
Although the reliability of racemization is in question, given the habitat of the Bowhead Whale, the reliability of their food source and their slow metabolism, such longevity would certainly seem possible.
Is it possible that a Bowhead Whale might outlive an Aldabra Tortoise to become the longest lived vertebrate? It would need to beat the record set by Adwaiter
of 256 years.