What disturbs our dreams more than a huge, wide-open mouth full of teeth and ready to swallow us? The mouth is that of the gigantic shark from Jaws , the film directed by Steven Spielberg in 1975 which inaugurated the season of "squalophobia" - or, as experts call it, selacophobia. Fear towards the great predators of the seas has been fueled since ancient times by legends and myths, but in very recent times it has been manipulated by books and films, up to the recent b-movies in which sharks are little less than grotesque Godzilla-like monsters . Result? The general public knows less about it than they did forty years ago. Thus, news that reveals all the weakness of the rulers of the seas risks going unnoticed.

Depth . A study by the Massachusetts Institute of Technology shows that great white sharks are venturing into increasingly deeper waters and further away from the Atlantic coast of the USA. Why? A possible answer: to escape the only real enemy - man - and the fishing boats that catch many specimens every year.

Plastic . The Center for Ecology and Conservation at the University of Exeter reveals that hundreds of sharks and rays risk dying entangled in plastic every year. As if that weren't enough, the indirect intake of plastic in the diet is now common: in fact, significant quantities of polyvinyl chloride, a common microplastic in the oceans, have been detected in sardines and other blue fish, which are part of the diet of sharks (and of men, among other things).

Poisons . Research carried out on 43 white sharks off the coast of South Africa confirmed significant concentrations of mercury, arsenic and lead in their blood. The levels do not yet seem alarming, but they indicate the certain presence of these toxins in prey and consequently of dangerous polluting substances even in the seas furthest from industrialized coasts.

Acidification . According to researchers at the South African University of Stellenbosch, the acidity of ocean waters - due to rising levels of carbon dioxide - is increasing. This phenomenon could lead to corrosion of sharks' teeth and scales, with a more significant and potentially lethal impact on some species than others.

Finning . It is a cruel and illegal practice in many countries around the world, but not all. The dorsal fins of captured sharks are cut off, then the injured specimens are often thrown back into the sea, where they die after long suffering. According to experts from the Californian association Sylvia Earle Alliance - Mission Blue, finning is a global problem and began in the 1980s. Shark fins can be worth 100 dollars a kilo: it is a big business, attracting Taiwanese businessmen to countries such as Spain, Costa Rica, Mexico, Ecuador. The fins purchased directly from local fishermen they are sent to Hong Kong, which is the hub of Taiwan's finning industry. And from Hong Kong they are distributed throughout Asia, in a rich commercial flow.

So the shark, one of the oldest living species on the planet, is officially at risk of extinction: starting from the mid-twentieth century, all research highlights a drastic decline in the population. It may be that sharks are still little loved, and the fear of them is alive, especially among those who don't know them. What is certain is that behind their terrible mask lies a fragile dominator.

The drawings that accompany this article are taken from the book Sharks, the rulers of the seas (original title: PNSO Marine Life Museum - Sharks and Their Relatives ) by Zhao Chuang and Yang Yang, in which scientific sheets and fabulous color plates describe in a realistic way the most impressive species.