Scientists and volunteers with The Marine Mammal Centre and California Academy of Sciences performing a necropsy on a beached grey whale on Tuesday in California to study the cause of death.
After breeding in the coastal lagoons of Baja California, grey whales are now making their annual trip to Alaska to feed, but their journey this year has been fraught with peril.
So far, seven migrating whales have been reported dead in the San Francisco Bay in the past month.
It was found that four of the whales died from malnutrition, which is rare, and three from ship strikes, which is not unusual.
Dr Steven Swartz, a marine biologist who has studied whales of the San Ignacio Lagoon in Mexico for over 40 years, observed more skinny whales this past winter.
"If there is enough food to support 25,000 whales, then they're fine," he said.
"If oceanographic conditions are changing and that volume of food production is not happening… we're going to see a reduction in grey whale populations," he added.