How do people know what they know about sharks, from how old they are to where they go? Start with age, the first thing to count. People can estimate how old a shark is by counting growth bands, like rings, in its backbone, and the count depends on how often a band forms. Sharks have no bones, and their skeleton is made of cartilage. For shortfin mako sharks, the age estimate depends on whether the vertebrae add one growth band pair a year or two, which is why some studies assumed two, others one, and recent work found one a year.

Radiocarbon can check a count. Bomb radiocarbon is carbon-14 left by nuclear-bomb testing. People tested it in the growth bands of whale shark backbones, and it showed the sharks add one band every year, so counting the bands gives the shark's age. As of November 2026, the oldest age seen for the species is one whale shark that was 50 years old when it died. The bomb tests of the 1950s and 1960s left radiocarbon in the ocean, and it was used to age white sharks. In that work, one male white shark was about 73 years old, far older than earlier estimates.

Counting does not work on every shark. The Greenland shark's age was worked out by radiocarbon dating the center of its eye lens, because its soft vertebrae have no growth bands. The largest shark in the study, about 5 meters long, was put at 392 years old, give or take 120, and the arithmetic goes like this: 392 minus 120 is 272, and 392 plus 120 is 512, so the range runs from about 272 to about 512 years, which spans 240 years (512 minus 272). As of November 2026, Greenland sharks are thought to reach adulthood only at around 150 years old, and they grow roughly 1 cm a year or less, which hinted that they live far longer than other vertebrates.

Tags and pictures follow and count sharks. A pop-up satellite tag records a shark's swimming depth and the water temperature in places where people cannot watch it. Scientists tracked white sharks with these tags to the White Shark Cafe, an area of open ocean halfway between Hawaii and Mexico. Satellite tags showed that some white sharks tagged off California swim all the way to Hawaii and back. Pictures count sharks too. In 2011 people counted about 219 mature and sub-adult white sharks off Central California by photographing dorsal fins, whose markings are unique to each shark, and each whale shark has its own spot pattern, like a fingerprint, so people can tell them apart in pictures.

Bite counts depend on a definition. The International Shark Attack File calls a bite unprovoked only if a live person is bitten in the shark's natural habitat with no provocation of the shark. It calls a bite provoked when a person starts the contact, for example by grabbing a shark or feeding it. As of November 2026 there are about 70 unprovoked bites on people worldwide in a typical year. Of the hundreds of kinds, three account for most of them: the white, tiger and bull sharks. Under that definition, as of November 2026 the file had confirmed 65 unprovoked shark bites worldwide in 2025, close to the recent averages of 61 a year from 2020 to 2024 and 72 a year over ten years.

Some answers come from experiments. In a smooth dogfish experiment, people gave odor to each nostril separately, with controlled strength and timing. The sharks turned toward the nostril that smelled it first, even when the other side got a stronger dose. When the gap between the two sides reached one second, they were no more likely to turn one way than the other. In a separate Florida experiment, people put 20 bonnethead sharks in magnetic conditions that matched places hundreds of miles from where they were caught. When the magnetic cues made the sharks seem to be south of where they should be, they began to swim north.

Fossils are how we know about sharks that are gone. A shark's skeleton is made of cartilage, which breaks down after death, so teeth are the part most often found. Megalodon was one of the largest sharks that ever lived, and it is extinct and known mostly from its teeth. Fossil megalodon teeth from Panama's Gatun Formation are mostly very small. Comparing them with the same tooth positions in adult and juvenile tooth sets showed they came from small individuals, not just small teeth from large jaws. Tooth size puts most of these sharks in the newborn or juvenile stage, from about 7 feet up to about 35 feet long, so scientists think the place was a shallow-water nursery.

Words to know

• vertebrae: backbone bones
• radiocarbon: age-test carbon
• megalodon: giant extinct shark
• juvenile: young
• unprovoked: not started