KYIV (NYTIMES) - Dolphins burned from bomb or mine explosions. Several thousand suddenly found dead, some washed up on the coasts of Bulgaria, Romania, Turkey and Ukraine.

The sudden and mysterious death of so many of the elegant marine mammals is raising alarm among some scientists that the war in Ukraine may be taking a growing toll on life in the Black Sea.

The battles waged along Ukraine's coastline have done untold environmental damage and have interfered with dolphin's habitat, scientists say. But the war has made it impossible to gather detailed information, leaving the dolphin deaths a mystery for now.

Recent studies from Bulgaria, Turkey and Ukraine found that marine biodiversity is under growing threat because of the war, including from bombs dropping in coastal feeding areas, oil from sunken ships and river runoff polluted by chemicals used in ammunition.

Ivan Rusev, an environmental scientist at Ukraine's Tuzla Estuaries National Nature Park, said data collected by his organisation since the start of the war indicated that several thousand dolphins have been killed. He said increased ship noise and use of powerful sonar systems may also be disorienting dolphins, which use sound to navigate.

"Some of the dolphins had burns from bomb or mine explosions and they could no longer navigate and, of course, could not look for food," he wrote.

The Turkish Marine Research Foundation reported in March "an extraordinary increase" in dead dolphins washing ashore there. It said that dolphins were being caught in fishing nets and it was investigating why such incidents had grown in number, including whether military activity in the northern Black Sea was playing a role.

"Along with marine pollution, ship noise and low-frequency sonars are known to be a serious threat to the marine species, especially to dolphins, which utilise underwater sounds actively to feed and navigate," the Turkish researchers said.

The Turkish Marine Research Foundation has also said the war is taking a devastating toll on broader marine biodiversity.

The Russian navy dominates the Black Sea off the coast of Ukraine and has imposed a blockade on all Ukrainian shipping. Russia waged brutal campaigns to win control of several key Ukrainian ports along the Black Sea and the adjoining Sea of Azov, and its warships patrol the waters around Ukraine.

Before the war, 100 scientists representing an international cetacean conservation treaty group and employing 10 aircraft and six ships surveyed marine life in the Black Sea and Mediterranean area. They found that the Black Sea was home to more than 253,000 dolphins, a healthy number that scientists said offered a positive ecological indicator of the overall ecosystem.

Now, however, it remains to be seen what the final toll of war may be on dolphins and other marine life.