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Great white sharks are disappearing from the Mediterranean: why that’s not good news
Great white shark numbers in the Mediterranean Sea have declined rapidly, a new study highlights. The predator’s disappearance would have a significant impact on the entire ecosystem.
Apex predator populations are diminishing throughout the world, as many such species face the threat of extinction. Their loss is capable of triggering a severe chain of events affecting entire ecosystems. This is true for land predators such as lions and tigers, as well as marine hunters like sharks. For example, the greatest of all sea predators, the great white shark (Carcharodon carcharias), also known simply as white shark, risks disappearing entirely from the Mediterranean Basin.
Fewer great white sharks in the Mediterranean
The drop in the white shark population was revealed by Abundance and distribution of the white shark in the Mediterranean Sea, a study conducted by a group of researchers from La Sapienza University in Rome, Italy in cooperation with Stanford University and the University of Virginia, both in the US. The research was supported by the Institute for Marine Biological and Biotechnological Resources (IRBIM) of the Italian National Research Council (CNR), the Anton Dohrn Zoological Station, a research institute in the Italian city of Naples, and the Italian National Institute For Environmental Protection and Research (ISPRA). For the first time ever, scientists estimated the white shark’s presence in the area over the last 160 years.
An elusive and irreplaceable presence
Great white sharks are renowned for their huge size, which may lead us to think that these creatures exist only the vast expanses of the ocean. It may therefore come as a surprise that the CNR’s research reveals that they’ve inhabited the Mediterranean Sea for centuries, a claim backed by recorded sightings dating back as far as Medieval times.
Despite the species’ classification as “critically endangered” by the International Union for Conservation of Nature (IUCN), an effective conservation programme can’t be undertaken in the absence of information regarding its status in this area. In response to this, the study seeks to collect a wide range of data to construct a bigger picture of the white shark’s habitat as well as its population density and fluctuations in numbers.
The drastic decline in recent years
Researchers collected 773 observations documenting the presence of white sharks. Ranging from 1860 to 2016, the data was utilised to develop spatial and temporal models on shark populations. The results suggest a “complex trajectory of population change characterised by a historical increase and a more recent reduction since the second half of the 20th century”.
The decline of white shark populations has been more prominent in some areas. “The decrease wasn’t homogenous throughout the Mediterranean Basin,” Giovanna Jona Lasinio, associate professor in La Sapienza’s Department of Statistical Science, explains. “For instance, in central Mediterranean sectors, a 52 per cent decrease was observed, whereas in the Marmara Sea the decrease was 96 per cent. Moreover, the reduction often comes with a decrease of spatial distribution, data often linked to endangered populations”.
What if sharks become extinct?
The great white shark is an apex predator, which means that it’s at the top of the food chain and doesn’t have any natural predators: its extinction would affect the food chain significantly. For example, it would cause an increase in its prey. “It has been demonstrated that removal of the apex predator from marine ecosystems leads to disastrous cascading effects on the whole trophic chain – in the words of Stefano Moro, from La Sapienza’s Environmental Biology Department –. From this point of view, the Mediterranean Sea represents a negative first place on a global scale, recording more than 50 per cent of shark species classified as ‘threatened’ by the IUCN on a regional level”.
Why sharks are at risk
We still don’t fully comprehend what the consequences of diminishing shark populations are. One thing, certainly, is that human impact has played a major role in falling numbers, as these animals tend to be the unfortunate victims of bycatch along with direct fishing and anthropic activities in coastal areas. 47 different shark species inhabit the Mediterranean, 20 of which are top predators, and they’re not only decreasing in numbers but also in size. Among them are great white sharks, frail shadow of the monsters who once terrorised the seas, but who now belong mostly to myths and tales of the past.
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