Biologists at the Santa Barbara Museum of Natural History presented results of necroscopies of blue whales that washed up on local beaches last fall: the whales were killed by ship strikes. They surmise that the whales were in shipping lanes because the krill was there, and that the whales probably didn't hear the ships approaching, because they were directly in front or because of background noise.
Last fall, after the blue whale deaths, ships deliberately slowed to 10 knots in the shipping lanes; that may have given whales more time to get out of the way. We'll see where the krill shows up this year, and whether the ships slow down.