A Greek marine conservation group says a "very unusual" increase in Aegean Sea dolphin deaths in recent weeks may be linked to Turkish naval exercises in the area.

Fifteen dead dolphins have washed up on the eastern island of Samos and other parts of Greece's Aegean coastline since late February, according to the Archipelagos Institute.

Its head of research, Anastassia Miliou, told The Associated Press on Monday that 15 is worryingly high compared to "one or two" in the same period last year.

The group said while it's still unclear what caused the deaths, the spike follows the Feb. 27-March 8 large Turkish navy drills that used sonar and practiced with live ammunition. The deafening noise of sonar can injure dolphins, with sometimes fatal consequences.