The question of a shark’s average lifespan does not have a simple answer because the group is so diverse. Sharks belong to the class Chondrichthyes, a collection of cartilaginous fishes that exhibit massive variation in size, habitat, and life history across hundreds of species. The longevity of these animals spans an enormous range, from a couple of decades to multiple centuries. This variation means that any single “average” figure would be misleading, as the difference in lifespan across the shark family is one of the most extreme in the vertebrate world.
The Challenge of Determining Shark Age
Determining the age of a shark presents a unique scientific challenge because, unlike bony fish, their skeletons are composed of cartilage, not hard, calcified bone. The most common method relies on counting growth bands, or annuli, found in the calcified portion of their vertebrae, similar to counting the rings in a tree trunk. To make these subtle bands visible and countable, scientists typically cut thin sections from the vertebrae and often enhance them using special staining techniques. This technique generally provides accurate age estimates for younger, faster-growing sharks.
However, the growth bands become narrower and less distinct as a shark ages, making the counts unreliable and often leading to an underestimation of the true lifespan for older individuals. To validate whether a band is deposited annually, researchers employ bomb radiocarbon dating. This method uses the spike of the Carbon-14 isotope absorbed into the marine food web following atmospheric nuclear weapons testing in the 1950s and 1960s. By measuring this distinct radiocarbon signature in the vertebral bands, scientists can confirm the rate at which the bands are formed and validate age estimates for older animals.
Lifespan Extremes The Shortest and Longest Lived
The breadth of shark longevity is understood by examining species at the extreme ends of the lifespan spectrum. Many smaller, coastal shark species have relatively brief lives. For instance, the Blue Shark has an estimated lifespan of only about 15 to 16 years. Various small dogfish or catsharks also mature quickly and live for a short duration, representing a faster life history strategy.
Conversely, the Great White Shark represents a mid-range lifespan, with recent studies revising earlier estimates. While they were once thought to live for around 30 years, bomb radiocarbon dating has revealed that Great Whites can live for much longer, with some large males estimated to reach ages of up to 73 years. The Whale Shark, the largest fish in the ocean, also exhibits a long lifespan, with validated ages reaching at least 50 years, and estimates suggesting some may live over 100 years.
The most extreme example of longevity is the Greenland Shark, a colossal, deep-sea species found in the Arctic and North Atlantic oceans. This species has an estimated lifespan of at least 272 years, with the oldest individual studied estimated to be 392 years old. Scientists determined these extraordinary ages not by counting vertebral rings, which are too soft, but by using radiocarbon dating on proteins preserved in the shark’s eye lenses. This tissue does not change over the animal’s life, confirming its potential for extreme longevity.
Biological Factors Influencing Longevity
The immense lifespans observed in many large and deep-sea sharks are closely tied to a biological strategy known as a slow life history. This strategy is characterized by slow growth, delayed reproduction, and extended longevity, which is a common pattern among deep-water species. Sharks that inhabit cold, deep-sea environments, such as the Greenland Shark, often possess extremely slow, efficient metabolisms.
This low metabolic rate, an adaptation to the frigid water temperatures, slows down bodily processes and is believed to reduce the rate of cellular damage and aging. This slow biological clock means that many larger shark species exhibit delayed sexual maturity. For example, female Greenland Sharks do not become capable of reproduction until they are 150 years old. Furthermore, many sharks display indeterminate growth, meaning they continue to grow throughout their lives, a trait associated with extended longevity.