Heavily used shipping lanes are crossing favored feeding areas of blue whales swimming off the West Coast of the United States, increasing the risk of injury and death for the marine mammals, researchers say.
Those threats to the whales could be reduced by modification of these shipping lanes between San Francisco and Los Angeles, they say in reporting their 15-year study of tagged blue whales tracked by satellites.
At least 100 strikes by ships on large whales happened up and down the California coast between 1988 and 2012, the National Oceanographic and Atmospheric Administration says.
Minor tweaks to heavily used shipping lanes could reduce that number, researchers say.
In the coast off Los Angles "you will eliminate many of the ship strikes on blue whales by moving the shipping lanes south of the northern Channel Islands," says Daniel Palacios of Oregon State University's Marine Mammal Institute.
Similar changes in the San Francisco region could also save whales, the researchers said in their study.
The tagged whales have been tracked to identify their important habitats and feeding areas and the timing of the whales' presence around major shipping ports, they said.
Researchers placed transmitters on 171 blue whales in California waters at various times between 1993 and 2008 that allowed them to tack the animals' movements by satellite.
"The main areas that attract blue whales are highly productive, strong upwelling zones that produce large amounts of krill -- which is pretty much all that they eat," says OSU researcher Ladd Irvine, lead author on the study published in the journal PLOS ONE.
"The whales have to maximize their food intake during the summer before they migrate south for the winter, typically starting in mid-October to mid-November."
At least two of the traditional main foraging regions are bisected by the West Coast shipping lanes, he says.
Such changes in shipping lanes to improve the safety of marine life are not unprecedented, and NOAA says the PLOS ONE study, the most comprehensive study of blue whales movements ever conducted, will be taken into account during a review of shipping lanes off the California coast.
"It is not often that research results are so applicable to a policy decision." Palacios says. "It's not really our place to make management decisions, but we can inform policy-makers and in this case it is pretty straightforward."
Until recently little was known of the range or breeding areas of blue whales, the largest creatures ever to inhabit the Earth.
Of the globe's estimated 10,000 blue whales, around 2,500 of them spend some part of their lives off the western coastlines of the Americas, often traveling from the Gulf of Alaska as far south as the equator.
