Every few years, a fishing boat off the Turkish coast drags up something that shouldn’t be there: a shark the length of a small car, thrashing in a net meant for anchovies. The photos go viral.
The internet asks the same question every time – how does a sea famous for having “no big sharks” keep producing monsters?
The short answer is that the question is built on a myth. The Black Sea and the Sea of Marmara are not shark-free.
They’re something stranger: a chemically hostile borderland where a handful of species survive permanently, while occasional giants slip through from the Mediterranean, get caught, get photographed, and vanish back into folklore before scientists can properly study them.
To understand why, you have to think of this whole region less as “a sea” and more as a three-story building with a broken elevator.
A Sea Divided Against Itself
The Mediterranean, the Sea of Marmara, and the Black Sea are connected – but only just. The Bosphorus and the Dardanelles are the two narrow straits stitching them together, and each one acts less like an open door and more like a security checkpoint with a very specific dress code.
The Mediterranean runs around 38 parts per thousand salinity – properly salty, the kind of water large predatory sharks are built for.
The Black Sea, fed by enormous rivers like the Danube and the Dnieper, sits at roughly 17-18 parts per thousand on the surface: barely more than half as salty.
Worse, below about 150-200 meters, the Black Sea turns anoxic – oxygen simply runs out, replaced by a toxic, hydrogen-sulfide-laced layer that makes the deep basin one of the largest dead zones on Earth. Nothing with gills survives down there.
The Sea of Marmara, sandwiched in between, is the compromise: a two-layer sea, with a thinner, fresher current flowing out from the Black Sea on top of a denser, saltier Mediterranean current creeping in underneath.
It’s an ecological corridor – and, crucially, it’s salty enough near the bottom for Mediterranean species to tolerate it, at least for a while.
The Only Permanent Resident: A Shark the Size of a House Cat’s Nightmare
If you want to meet a shark that actually lives in the Black Sea year-round, meet the Black Sea spiny dogfish (Squalus acanthias), locally known as katran.
It is, by a wide margin, the most abundant shark in the basin – and it is almost comically unthreatening.
Adults rarely exceed about 1.5 meters, they pose no danger to swimmers, and their only real weapon is a pair of mildly venomous spines in front of their dorsal fins that can leave a nasty scratch on a careless fisherman’s hand.
The spiny dogfish’s biology is almost the opposite of a Hollywood shark’s: it matures at 13-14 years old, carries its pups for up to two years, and can live for decades – a slow, patient survivor rather than an apex predator, which is exactly the kind of animal that thrives in a sea too fresh and too oxygen-starved for anything bigger.
A few other cartilaginous relatives – like the small-spotted catshark and various rays – round out the basin’s permanent, harmless cast.
That’s it. That’s the entire year-round shark population of the Black Sea. Everything else is a visitor.
Where the Real Giants Come From: The Sea of Marmara’s Revolving Door
The Sea of Marmara is a different story entirely, and it’s where the viral photos actually come from. Turkish marine biologists – most notably Hakan Kabasakal, who has spent decades cataloguing shark records in these waters – have documented a genuinely surprising cast of large species passing through, including thresher sharks, bluntnose sixgill sharks, and, remarkably, multiple historic records of great white sharks in and around the Sea of Marmara and the Bosphorus.
A few of the recurring headline-makers:
- Thresher sharks (Alopias vulpinus). Recognizable by a scythe-like tail fin nearly as long as their body, these predators follow migrating schools of bonito, mackerel, and anchovy into the Dardanelles and Marmara each spring and autumn. Catches of 3-4 meter specimens (tail included) by commercial netters near towns like Bandırma and Silivri have made local news repeatedly over the past two decades.
- Bluntnose sixgill sharks (Hexanchus griseus). A genuinely ancient-looking deep-water species, normally a resident of dark offshore depths, that has turned up in nets in the Sea of Marmara at sizes topping three meters and several hundred kilograms.
- Basking sharks (Cetorhinus maximus). The second-largest fish in the ocean, capable of exceeding 7-8 meters – and, despite the terrifying scale, completely harmless, filtering plankton through a gaping mouth rather than hunting anything at all. Its presence tends to track seasonal plankton blooms rather than prey migrations.
- Great white sharks (Carcharodon carcharias). The rarest and most contested of the group. Historical and modern records – compiled largely through Kabasakal’s research – describe a small number of white shark catches in the Sea of Marmara and near the Bosphorus, dating back over a century. They remain exceptional events, not evidence of a resident population.
The pattern is consistent: these are Mediterranean and Aegean animals pulled north by the same forces that pull in the tuna and sardines they eat, funneled through the Dardanelles into Marmara’s saltier bottom layer, where they can survive – for a while.
Why They Never Stay
This is the part the viral headlines always skip. None of these Mediterranean giants are colonizing the Black Sea. The osmotic math simply doesn’t work.
A shark physiologically tuned to 38 parts per thousand salinity, dropped into water at half that concentration, faces real physiological stress – and that’s before it reaches the anoxic dead zone lurking beneath 150-200 meters. The Black Sea isn’t a habitat for these animals; it’s closer to a trap.
So the giants that make it into Marmara are, functionally, tourists – following a food source, occasionally overshooting into the Bosphorus, and rarely if ever making it deep into the true Black Sea.
Researchers note that some species once reported historically along the Bulgarian and Romanian coasts in the early-to-mid 20th century – thresher sharks included – have gone largely unreported in the Black Sea proper for decades, reinforcing that these were always marginal, opportunistic incursions rather than an established range.
So, Are There Sharks Lurking in the Black Sea?
Yes and no – and that “no, but actually yes, sort of” is precisely what makes this region so strange. The Black Sea itself hosts exactly one common, harmless, slow-growing shark species and essentially nothing larger.
But sail two straits south, into the Sea of Marmara, and you’re in genuinely unpredictable water – a narrow, half-salty channel where, every few years, something enormous, ancient, and rarely seen surfaces in a fishing net, gets its fifteen minutes of local fame, and disappears back into a sea that was never supposed to hold it in the first place.
Sources and Further Reading:
- Kabasakal, H. – Shark biodiversity in the Sea of Marmara: Departures and arrivals over a century, Marine Biodiversity Records (Cambridge Core)
- Kabasakal, H. – The status of the great white shark (Carcharodon carcharias) in Turkey’s waters, Marine Biodiversity Records (Cambridge Core)
- Kabasakal, H. – Incidental captures of thresher sharks (Lamniformes: Alopiidae) from Turkish coastal waters, Annales, Series Historia Naturalis
- Occurrence of the Pregnant and Young Thresher Shark Alopias vulpinus in the Northeastern Mediterranean Sea, International Journal of Zoological Research
- IUCN Red List of Threatened Species – species distribution records for the Black Sea (hai.swiss shark database)
- Shark attacks against humans and boats in Turkey’s waters in the twentieth century, ResearchGate
- Journal of the Marine Biological Association of the United Kingdom – historical note on thresher shark occurrence in the southwestern Black Sea
/This article is intended for general educational and travel-interest purposes. Shark population data and conservation status should be verified against current IUCN Red List assessments for the most up-to-date figures./
