Sharks and Rays Flee Dying Marmara: Oxygen Crisis Drives Protected Species to Shore
Shark Populations in the Marmara Sea
As oxygen levels plummet in the depths of the Marmara Sea, an alarming rise in coastal shark and ray sightings is signaling an unfolding ecological crisis, warns WWF-Türkiye on the occasion of Shark Awareness Day (July 14).
According to Dr. Hakan Kabasakal, cartilaginous fish expert for WWF-Türkiye, the increasing presence of species like the spiny dogfish (Squalus acanthias), thornback ray (Raja clavata), and bramble shark (Echinorhinus brucus) near shores is not due to a population boom but rather a desperate search for oxygen. These species are all protected under Türkiye’s Aquatic Resources Law No. 1380.
“This isn’t a resurgence—it’s survival,” says Dr. Kabasakal. “The deep Marmara is becoming uninhabitable. These creatures are fleeing dead zones.”
Dead Zones Expanding as Oxygen Levels Collapse
The crisis is driven by a process known as hypoxia (low oxygen) and anoxia (zero oxygen), which has spread rapidly across global marine environments. Since 1960, the world’s oceans are estimated to have lost 2% of dissolved oxygen, a change linked to global warming, disrupted ocean circulation, and nutrient-rich agricultural runoff.
Today, over 250,000 km² of ocean is affected by these so-called “dead zones.” The Marmara Sea is now among the worst hit, especially its eastern basin, where oxygen levels have dropped below 2 mg/L, threatening marine life across the board.
Sharks and Rays Retreat to Shallow Waters
Species that were once exclusive to the deep sea—such as Raja radula and Raja clavata—are now being observed in coastal waters as shallow as 6 meters, a stark shift in behavior caused by deteriorating habitat conditions. These sightings have triggered controversial debates about removing protection statuses for some endangered species.
Dr. Kabasakal warns against misinterpreting the trend:
“Short-term increases near the coast aren’t signs of recovery—they’re red flags.”
Human Impact at the Core
The main culprits? Industrial waste, urban pollution, agricultural chemicals, and untreated discharges from millions living along the coast, combined with pollution flows from the Black Sea. This environmental burden has been mounting for over four decades, and the Marmara Sea is now suffocating.
“We are the cause,” says Dr. Kabasakal. “And unless we restore oxygen levels in the deep waters, we shouldn’t be surprised if Marmara turns into a marine desert.”