Scientists are investigating whether the BP oil disaster, an extreme cold snap, or even a case of the measles has killed nearly 90 bottlenose dolphins in the Gulf of Mexico.

Since the start of the year, 87 bottlenose dolphins have washed up on the coasts of Louisiana, Alabama, Mississippi, and along the Florida panhandle, Kim Amendola, a spokeswoman for the National Oceanic and Atmospheric Administration said. That's about 12 times higher than typical strandings at this time of year.

Forty-six of those were infants or still-born.

The coastal areas were the worst affected by BP's blown-out well, which spewed 4.9 million barrels of oil into the Gulf of Mexico.

The die-off had prompted fears that exposure to toxins from the BP spill had interfered with last year's calving season, causing miscarriages.

However, scientists at the Dauphin Island sea lab in Alabama suggested the dolphins may have succumbed to the cumulative stresses of the BP spill, disease such as the outbreak of a measles-type illness, or a sudden gush of extremely cold fresh water from the Mississippi – all of which lowered their resistance.

"The ultimate frustration in all of this is that unless they find a heavy body burden of toxins that can be attributed directly to the oil from BP's well than I am afraid we are never going to find an answer," said George Crozer, the director of the lab.

"The oil spill is probably the most probable cause that we have now, but there are actually lots of other factors, and my bottom line is that it is a cumulative effect of all the stresses the dolphin population has been subjected to over the last year."

In addition, he said a decline in the Gulf's shark population may have left more dolphin carcasses to wash to shore, rather than being eaten at sea.

Dolphin carcasses have been sent off to be tested for exposure to toxins related to the BP spill.

"Right now nothing has been ruled out – chemical, biological, even cold weather," an official at the Institute for Marine Mammal Studies said.