The ghosts of the Mediterranean: What a rare great white shark sighting could reveal about a changing ocean

Headlines were made this week when scuba divers removing abandoned ghost nets from a shipwreck between Tunisia and Sicily filmed an adult great white shark. The footage  quickly made global news, yet the real story is not that a great white was seen in the Mediterranean, but that many people were surprised by its presence at all.

Great white sharks (Carcharodon carcharias) have always been part of the Mediterranean ecosystem. Historical records stretching back more than 150 years document their presence across the region, from Spain and France to Italy, Malta and Greece. Although never abundant, they were once encountered more frequently than today. Over time, fishing pressure, prey depletion and accidental capture reduced populations so severely that sightings became exceptionally rare.

Not extinct, but rarely observed

Today, Mediterranean great whites are often described as a “ghost population”: not extinct, but rarely observed. Most modern evidence comes from isolated encounters, such as fishermen’s reports, photographs or brief videos. Many reports remain difficult to verify, contributing to the species’ mystery. Some assume these sharks are simply lost individuals entering through the Strait of Gibraltar, but research suggests otherwise.

A 2020 genetic study, led by the University of Bologna, revealed that Mediterranean great whites are unique. By analysing DNA from historical shark remains, researchers found that this population has been isolated for around 3.2 million years, making it one of the oldest and most distinct white shark populations on Earth. Their DNA is more closely related to Pacific populations than to those in the neighbouring Atlantic, indicating a complex evolutionary history. The study also found extremely low genetic diversity, suggesting a small and fragile population shaped by a founder event or bottleneck. The population is considered critically endangered, and its low genetic variability may increase its vulnerability. As a distinct lineage, its loss would represent a significant decline in global white shark diversity.

Despite confirming long-term persistence, the study highlighted a major knowledge gap: little is known about the species’ distribution, habitat use or population trends in the Mediterranean. This presents a serious conservation challenge, as it is difficult to protect a species without understanding where it feeds, migrates or reproduces.

Recent evidence reinforces the idea that Mediterranean great whites still persist, albeit in very low numbers. In April 2023, tuna fishermen accidentally caught a juvenile great white around 20 nautical miles off Alicante, Spain. Just over two metres long, the shark was genetically confirmed as Carcharodon carcharias. Because it was a juvenile, scientists questioned whether parts of the western Mediterranean may still function as developmental habitat or nursery areas. While not conclusive, this suggests the population may be more ecologically important than assumed.

Why are encounters becoming more common?

Combined with the recent adult sighting in the Strait of Sicily, this evidence points not to a species returning, but one that never fully left. The question is why such encounters are becoming more visible now.

Part of the answer lies in improved monitoring, including the availability of advanced underwater cameras, satellite tracking and citizen science and reporting, meaning unusual encounters are now far more likely to be documented. However, environmental change may also be influencing when and where sharks are observed.

Marine ecosystems worldwide are undergoing rapid transformation. Ocean temperatures are rising, prey distributions are shifting, and species are responding by altering their movements and behaviour. Great white sharks, as highly mobile apex predators, are particularly sensitive to these changes. Importantly, increased sightings do not necessarily indicate population recovery. Climate change often redistributes species rather than increasing their numbers.

As waters warm and prey shifts, sharks may appear in locations where they were historically uncommon or arrive at different times of year.

Evidence for these shifts is emerging globally. Along the eastern seaboard of North America, researchers have documented changes in great white shark movements, including in Florida and the Gulf of Mexico.

Satellite-tagging studies show that shark movements are closely linked to environmental conditions and prey availability, with individuals adjusting their distribution accordingly .

This highlights that apex predators respond to multiple interacting factors, including climate, prey availability and habitat conditions. From this perspective, the Mediterranean sighting is not an isolated curiosity but part of a broader pattern of ecological change.

What this means for conservation

The sighting has prompted calls for greater marine protection, including expanded marine protected areas. However, this raises a key challenge: where should protection begin? Great white sharks are highly mobile and cross national boundaries, meaning conservation cannot rely on protecting single locations. It requires identifying critical habitats such as migration routes, feeding grounds and potential nursery areas that may span multiple countries.

The Strait of Sicily, where the recent footage was captured, is both a major biodiversity hotspot and a heavily exploited marine region. If great white sharks continue to use this area, understanding their movements could become central to conservation planning.

Ultimately, the importance of this sighting lies not just in the shark itself, but in what it reveals about how little we still know. More than 150 years after the first records, scientists remain uncertain about where Mediterranean great whites spend most of their lives, whether nursery areas still exist and how many individuals remain.

Recent evidence suggests persistence rather than disappearance. The 2023 Alicante juvenile and the Strait of Sicily sighting together indicate that the Mediterranean is not devoid of great white sharks, but a low-density, poorly observed range where a long-standing population still exists.

The challenge now is no longer proving their presence, but protecting a critically endangered apex predator when we are still discovering how it uses its environment. As climate change and fishing pressure continue to reshape marine ecosystems, the ghosts of the Mediterranean may offer important insights into the future of our oceans.