(CNN) Ocean scientists are concerned about dead gray whales that have washed up on the US West Coast this year at the highest rate in almost two decades.

As of Thursday night, 58 gray whales have landed ashore from California to Alaska, compared to 45 for all of last year, the National Oceanic and Atmospheric Administration said. Some were underweight, leading scientists to think they did not have enough food.

"Why these whales are malnourished is the mystery we are trying to unravel," NOAA spokesman Michael Milstein said. "Something is going on."

The last time researchers saw such high numbers was in 2000, when 131 deaths were documented.

Climate change could be contributing, Milstein said. "That's an angle they're investigating," he said. "We don't know anything for sure at this time."

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