The first direct observations of blue whales trying to avoid oncoming ships in the open sea reveal that the animals are simply ill adapted to maneuver quickly enough, according to a study from Stanford University.
"It's not part of their evolutionary history to have cargo ships killing them, so they haven't developed behavioral responses to this threat," said Jeremy Goldbogen, an assistant professor of biology at Stanford's Hopkins Marine Station, and the senior author on the study, in a press release.
"They simply have no compelling response to avoiding these dangerous ships."
The researchers hope to formulate a plan for pleasure boaters and shipping companies to better avoid slow-moving whales like blues and humpbacks.
Collisions with ships in busy shipping lanes is a major threat to the existence of large whales, including the blue whale.
Until now, efforts have concentrated on slowing down ships - a whale speed limit - or re-routing routes around major whale breeding areas. Direct data was nonexistant.
The Standford researchers set out to correct that by attaching GPS to a number of blue whales off Long Beach, Calif., with suction cups.
They tracked nine whales for 24 hours, observing them crossing paths with 20 ships and then cross-referencing the movements with boat traffic. Distances between the ships and the whales ranged from 60 meters to more than 3 kilometers.
What they found was that the blue whales' startle-and- response to an approaching ship was to play dead, when what they needed to do was to dive and get the hell out of the way, quickly.
Instead, the whales floated horizontally down through the water, like gigantic leaves.
"Blue whales have a subtle and not very convincing ability to get out of the way of oncoming ships," said Goldbogen in the press release.
"Instead of diving, where the animal kicks tail up and goes down vertically, they just sink horizontally. This results in a slow dive and leaves them susceptible to ship strikes."
In order to escape unharmed from a passing ship, a whale has to dive at least 30 meters to avoid the propeller's suction.
The observed whales sank at about a half a meter per second, hardly fast enough to get out of the way.
Next up: another round of whale tracking, including humpback whales, to get more data on whale behavior in busy shipping lanes. Then the team will set out to make recommendations.
The study was published in Endangered Species Research.