In April 2023, local fishermen off the coast of eastern Spain, incidentally caught something massive within the country’s Exclusive Economic Zone (EEZ). Genetic analysis confirmed its species as Carcharodon carcharias, the great white shark.
Sightings like this are significant for multiple reasons. Firstly, great whites are among the most important members of the oceanic megafauna, playing critical roles as apex predators and maintaining trophic balance in marine ecosystems. Also, their population has declined by an estimated 30%-49% over the past 159 years, and the species is currently listed as Vulnerable by the International Union for Conservation of Nature (IUCN).
So when this shark was surprisingly sighted in 2023, it prompted scientists to probe deeper. They reviewed previously documented occurrences, found patterns, and tied them to this new event. Their observations were recently published as a paper in Acta Ichthyologica et Piscatoria.
An earlier review had documented 62 Spanish cases, between 1980 and 2016, including nine indirect findings such as bite marks in stranded sea turtles. The scientists swept historical records further and discovered additional evidence of shark sightings dating as far back as 1862.
These sightings seem sporadic, and their rarity has so far suggested a decline in the population of the great whites. But after going through the records and linking previous sightings with this latest event, the researchers suggest that the great whites might actually never have left the Mediterranean waters, but persist within it as a “ghost” population: rarely seen, but never truly gone.
Furthermore, these ‘random’ sightings might actually be following a structured pattern.
“When the full historical record is analyzed, these sightings appear to be consistent over time rather than sporadic anomalies,” said Dr. José Báez, lead author of the paper.
It is also important to note that the 2023 catch was juvenile. It weighed between 176-198 lb (80-90 kg) and measured approximately 82 inches (210 cm) in length. According to studies over the years, two major breeding zones have been identified within the Mediterranean waters: one in the central Mediterranean, particularly around the Strait of Sicily and the Gulf of Gabès, and the second in the Bay of Edremit in the northeastern Aegean Sea.
Sighting a juvenile off the Spanish coast raises new questions: do the great whites have another breeding zone closer to the Spanish coast, which we have yet to identify, or was this individual born in established nursery grounds before migrating to the region? While the latter appears more likely, according to Dr. Báez, confirming either hypothesis would offer insight into how great whites inhabit and move through the Mediterranean.
“Most importantly,” he said, “it would further support the idea that a biologically active and potentially endemic population of great white sharks exists in the basin. Evidence of reproduction within the Mediterranean would indicate that the population is not merely composed of transient individuals from the Atlantic, but rather that it maintains its own life cycle within the region.”
Another key insight from the historical patterns is that the sightings appear to be closely tracking the migration of bluefin tuna, an important prey species for great whites. The relationship between great whites and the bluefin tuna has been documented as an important example of predator–prey coexistence in the Mediterranean waters.
The Marmaric and Bosphoric waters, which have experienced a drastic decline in bluefin tuna numbers, have also seen a 96.6% decline in great white populations, suggesting that the ecological shift between these two species may be linked.
Additionally, there appears to be a shift in the distribution of great whites in the Mediterranean, with their movements closely mirroring those of bluefin tuna, which are moving in response to cooler sea-surface temperatures. The tuna movements are seasonal, and the sharks appear to be following suit, hovering along the Spanish coast in spring and summer, when tuna pass through on their own migrations.
“While we do not observe a clear increasing or decreasing trend, the records do show temporal patterns that are broadly compatible with seasonal movement dynamics. In particular, sightings tend to occur more frequently during the spring and summer months along the Spanish Mediterranean coast,” said Dr. Báez.
Ultimately, the 2023 catch is more than just an incidental finding of a shark pup. This study suggests that it may be part of a broader pattern, hinting at a population that has quietly persisted in the Mediterranean all along.
“From a conservation standpoint, these findings reinforce the importance of continuing research efforts in the region,” Dr. Báez said. “In particular, identifying and confirming potential breeding and pupping areas should be a priority. At the same time, conservation strategies should focus on minimizing anthropogenic impacts that could affect the population, including fisheries interactions and other human pressures within key habitats.”
