(KTVU) - There is an unusual sight in the San Francisco Bay. Experts say numerous gray whales are lingering in the area much longer than the normal day or two when they migrate towards Alaska.
Scientists say there's cause for concern because since March 10, seven have been found dead in various parts of the bay, including Pacifica, Richmond and San Mateo.
During the first week of April, the sight of a humpback whale in the San Francisco Bay delighted spectators since this month marks the start of the whale watching season for San Francisco Whale tours.
"This is a gray whale. This is a skinny individual," said Michael Pierson, a naturalist with the tour company as he showed a KTVU crew photos of a whale that was seen in the bay.
He says the skinny condition and the higher than usual number of gray whales in the area, plus the length of time they're lingering in the bay, are signs that they may be in distress.
"It's always concerning when you see this unusual behavior or these changes in behavior," said Pierson.
The change in behavior has proven to be deadly for seven gray whales. Researchers with the Marine Mammal Center in Sausalito have conducted necropsies.
They determined the first three found died of malnutrition. Four more turned up dead since April 10.Two appear to be a mother and her calf. They and another gray whale died after being struck by vessels.
"The younger animal had blunt force trauma-type injury. The older one had propeller strike injuries, deep cuts and her tail was completely severed off," said Dr. Padraig Duignan, chief research pathologist with the Marine Mammal Center.
Ship strikes are not unusual because San Francisco Bay is home to the second busiest port on the West Coast. But the high number of gray whales stopping here to forage for food is unusual.
Experts say necropsies are key to find out why.
"Hopefully when we piece all the parts of the puzzle together, we'll have a better idea. Right now, we're just gathering all this information," said Duignan.
Experts say they are very concerned that three gray whales have been killed by ship strikes in just two weeks. They hope to develop more information to ultimately prevent deaths.