SANTA ROSA (KRON) – The carcass of a 28-foot juvenile gray whale washed on Portuguese Beach this weekend.

This is the sixth dead whale to wash ashore since mid April, raising concern as to what is killing these enormous mammals.

Park officials say the whale came ashore on the Sonoma Coast on Friday night or Saturday morning, but that it had most likely been dead for some time.

California State Parks Ranger Damien Jones says the marine Mammal Center took a tissue sample in an attempt to determine the cause of death.UNUSUALLY HIGH WHALE DEATHS: SHOULD WE BE CONCERNED?

On May 19th, a dead grey whale appeared in Half Moon Bay. Two whales have recently washed up on the shore in Pacifica, one in April and one in early May. Also in April, a killer whale washed up near Fort Bragg.

Jones says the juvenile gray whale does not appear to have been killed by trauma, like being struck by a ship. The whale carcass will remain on the beach until a necropsy is performed.  Several of the other dead whales have been buried due to the odious stench.

We are now entering the final months of whale migration, so officials are hoping this trend stops.