Government officials and scientists in Peru are scrambling to find out why at least 877 dolphins and more than 1,500 birds have died since February, the New York Times reports. 

While the predominant theory is that the dolphins are dying of a virus and the seabirds starving to death because warmer coastal waters are killing off anchovies, not all residents are buying it. Some believe that seismic testing by oil and gas companies are the culprit. 

The dolphins, many of which appeared to have decomposed in the ocean before washing ashore, were found in the Piura and Lambayeque regions, not far from the border with Ecuador.

The seabirds, which seem mostly to have died onshore, have been found from Lambayeque to Lima. “Never in my 40 years as a fisherman have I seen anything like this,” said Francisco Ñiquen Rentería, the president of the Association of Artisanal Fishermen in Puerto Eten, in the Lambayeque region. “Sometimes in the past, you’d randomly see a dead dolphin or a pelican, but this, what’s happening now, is really alarming.”

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