The Hidden Language Of Shark Scars

Despite decades of research, some of the most basic facts about great white sharks (Carcharodon carcharias) remain unknown. We don’t know how long their gestation period is, where they mate or give birth, or how they interact with one another beyond occasional surface observations. Now, this isn’t due to a lack of interest or effort. Afterall, white sharks off central California are among the most studied large marine species in the world, with over 21,000 instrumented tracking days and even a fully sequenced genome! But the vastness of the ocean make consistent observation difficult, and many aspects of their lives still unfold out of our sight. Now, scientists are turning to a surprising new source of data: scars.

Over the years, underwater cameras and advances in photography have built up massive image libraries of individual white sharks, many of which have been photographed repeatedly over decades. These images are revealing patterns of scarring that scientists of a new study believe may hold the key to long-unanswered questions. Injuries show up in specific places and times, and by comparing these across individuals and years, researchers have begun to trace how white sharks live, where they go, what they eat, and who they fight or mate with. But before scars can become a reliable source of life history data, researchers first have to understand what caused them.

That’s exactly what a new study published in Frontiers sets out to do. By reviewing more than 2,500 video clips of over 500 individual white sharks filmed between 1987 and 2022 in central California, a team of scientists led by Dr. Scot D. Anderson of the California White Shark Project developed a classification system for different types of wounds. Each scar was placed into one of five major categories based on its shape, depth, location, and other visual cues: injuries from other sharks, prey interactions, environmental contact, parasites, or human-related damage. The team created a dichotomous key (a series of yes/no questions) to help other researchers consistently identify the cause of a wound. The hope is that by standardizing how these scars are interpreted, scientists can start using them as a reliable tool across white shark populations and potentially for other large marine species.

Some wounds are straightforward. For instance, shark bites leave clear crescent shapes from serrated teeth. Shallow, repetitive bites (called “hold bites”) are likely part of mating behavior, where males grip females whereas deep bites that cut across muscle and gill areas suggest aggression, possibly from dominance disputes. Scars caused by pinniped prey, such as seals and sea lions, often appear as paired puncture marks from canine teeth or raking scratches from claws. Even squid leave identifiable wounds: circular sucker marks tapering in size along the shark’s skin. Rare, but distinct. Then you have environmental scars, which come from contact with rocky seafloors or reef structures and appear as wide abrasions with frayed edges that tend to run along the shark’s body. Parasitic scars — caused by species like copepods or cookiecutter sharks — are some of the easiest to identify. Cookiecutter bites are unmistakable, leaving neat, golf ball–sized holes or half-moons where a small shark has taken a plug of tissue. Human-related wounds are also clear; boat propeller strikes leave evenly spaced parallel gashes, while fishing gear can cause rope burn-like abrasions or embed in fins and mouths. Even the scars from tracking tags are visible, with black ovals and a telltale line from the anchor.

The team says that what makes this dichotomous key valuable is its potential to reveal when and where key events in a shark’s life occur. White shark mating remains a mystery, but if researchers see fresh hold bites and cookiecutter marks healing at similar rates on the same individuals, it suggests both occurred around the same time and place (aka likely during the sharks’ open ocean migrations). Fresh pinniped-inflicted wounds appearing alongside mating marks on females? Could mean these interactions happen near coastal haulouts. And for younger sharks, prey-inflicted wounds could mark the transition to new diets as they grow. Thankfully, we know that white sharks have a predictable healing timeline. Their wounds start red or pink, fade to white, and eventually turn black before blending in with their natural skin tone. This helps scientists estimate when an injury occurred, giving further insight into shark movements and interactions. Not to mention that some scars remain visible for years, even decades, unless new injuries cover them; this longevity means long-term photo records can show not just the presence of wounds, but also their progression and frequency.

With this foundational classification system now in place, the hope is that future studies can use it to analyze large datasets across white shark populations. The team also believes that other species of large sharks with long-term photo records, such as whale sharks and basking sharks, could also benefit from similar approaches. Not all wounds will be clear, and not all can be classified, but enough can to build meaningful patterns.

This simple shift in perspective — looking at scars not as damage but data — might unlock a whole new dimension of marine science. You might have heard people say “Every scar is a story,” to make people feel better about the marks they have on their body. Well, the same can be said for sharks. And now, we’re learning to read them.