Mediterranean Sea Explorers Monitor Giant White Shark Movements
A group of scientists are on a mission to find white sharks in the Mediterranean Sea, but the task is turning out to be more complicated than expected. Despite not encountering a single shark, the team can still confirm their presence through scientific evidence.
Later, the team compares their search for the white sharks in the Mediterranean to finding a needle in a haystack. Led by Francisco Ferretti from Virginia Tech in Blacksburg, the group acknowledges the rarity of white sharks in the Mediterranean. However, they also mention in the journal "Frontiers in Marine Science" that this is exactly why it's important to search for them.
White sharks (Carcharodon carcharias) form a genetically distinct population in the Mediterranean. The International Union for Conservation of Nature (IUCN) categorizes them as "critically endangered," estimating that there are only 250 left, according to their data from 2016. The main reason for their decline is industrial fishing, which affects their food supply adversely. The Mediterranean is one of the most exploited seas worldwide.
In contrast to places like California, where sharks often gather near seal colonies, there are no known habitats for white sharks in the Mediterranean, making them difficult to locate.
Exhaustive Hunt
From 2021 to 2023, the U.S. team conducted a search for the animals in the Strait of Sicily, between Italy and Tunisia. Their aim was to identify the sharks' living areas and count their population to better protect them. Previous research teams had tried to attach electronic tags to the sharks without success.
However, Ferretti's team used environmental DNA (eDNA) in their search. This involves identifying DNA traces left behind by animals, such as through waste or scales. This allows researchers to confirm the presence of animals without needing to observe them directly.
Numerous Challenges
However, the researchers faced numerous obstacles. Due to the lack of their own research ship, they had to rely on alternatives such as fishing boats, which were not always available, or sailing boats and catamarans, which provide limited space. Additionally, there was a risk that the researchers' equipment could get entangled in fishing nets in the heavily fished area.
Despite these challenges, the team managed to collect 159 eDNA samples during their expeditions, thus confirming the presence of white sharks at four locations. They were unable to determine an exact number of animals. Using bait and cameras, the researchers also attempted to record the sharks on video. However, the lack of space often prevented them from bringing enough bait on board.
The research team did not actually spot a white shark, but they considered their expeditions a success. The data and information they collected are helpful for future expeditions. They also found that the Tunisian coast is likely one of the last refuges for white sharks, as the team discovered most of the eDNA samples from white sharks there. The team plans to focus its efforts on this area in the future.
It was already suspected that the animals reside mainly in the Strait of Sicily. Overall, the team concludes in the journal that developing a comprehensive monitoring program with year-round activities is now essential.
While the team was unable to physically encounter a white shark during their expeditions, the collected eDNA samples provided concrete evidence of their presence in the Strait of Sicily. Moreover, the predominance of eDNA samples found along the Tunisian coast suggests that this area may serve as a critical refuge for this endangered shark species.
