(CNN) Dead gray whales keep showing up along the west coast of North America, from Alaska to Mexico, and it has become a concern for marine biologists.

And you guessed it: The climate crisis is theorized as the leading cause for these deaths.

Over the July 4 weekend, seven dead gray whales were discovered in Alaska: four near Kodiak Island, two at Egegik and another at Takli Island.

These findings raise the death toll for gray whales in Alaska to 22 this year.

The National Oceanic and Atmospheric Administration declared an unusual mortality event for gray whales on May 31.

The criteria to define an unusual mortality event A marked increase in the magnitude or a marked change in the nature of morbidity, mortality or strandings when compared with prior records. A temporal change in morbidity, mortality or strandings is occurring. A spatial change in morbidity, mortality or strandings is occurring. The species, age or sex composition of the affected animals is different than that of animals that are normally affected. Affected animals exhibit similar or unusual pathologic findings, behavior patterns, clinical signs or general physical condition. Potentially significant morbidity, mortality or stranding is observed in species, stocks, or populations that are particularly vulnerable. Morbidity is observed concurrent with or as part of an unexplained continual decline of a marine mammal population, stock or species.

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