Blue whales cluster for long periods in the busy shipping lanes off the California coast, according to a new study that raises concern about collisions between vessels and the endangered animals.

“It’s an unhappy coincidence,” said Ladd Irvine, a marine mammal ecologist at Oregon State University who led the study published Wednesday in the journal Plos One. “The blue whales need to find the densest food supply. There’s a limited number of those dense places, and it seems as though two of the main regular spots are crossed by the shipping lanes.”

Irvine and his colleagues used satellites to track 171 tagged blue whales over 15 years. They produced the most-detailed maps to date of the feeding zones of the giant whales, which are protected from hunting under international regulations.

The biggest overlap between blue whales and ships occurs from July to October near the western Channel Islands off Santa Barbara, the researchers reported. They also found somewhat smaller overlaps near the Gulf of the Farallones off San Francisco, and at the northern edge of Cape Mendocino.


The study’s conclusions are at odds with previous research that suggested that shifts in shipping lanes would not help the whales because they are too widely dispersed. That research was based on whale sightings, which are more rudimentary than the tracking method used in the new study.

With the tags and satellites, Irvine’s group recorded individual whales over longer periods of time — an average of two to three months. One whale remained tagged for nearly a year and a half.

“This is far and away the most-detailed look that we’ve gotten on where these whales go,” Irvine said.

Monica DeAngelis, a marine mammal biologist with the National Oceanic and Atmospheric Administration who has worked to protect whales from collisions with ships, said the satellite data produces a more accurate long-term picture of the animals’ movements.


“It gives us a lot more insight into what whales are doing,” said DeAngelis, who was not involved in the study.

The largest animals on Earth, blue whales can grow to more than 100 feet long and weigh 150 tons. About 2,500 of the estimated worldwide population of 10,000 congregate in the waters off the West Coast.

In 2012, the International Maritime Organization agreed to divert southbound ships more than a mile away from Santa Cruz and Santa Rosa islands, off Santa Barbara, and elongated another lane in the Gulf of the Farallones. Both changes were prompted by increased blue whale sightings near areas where an upwelling in deep sea currents dishes up dense schools of krill, the whales’ primary food source.

The changes took years to implement, and any new dialogue about further shifts is expected to take awhile, said DeAngelis, who helped coordinate the effort.


The shipping industry, which has supported additional research on whale populations and behavior, is somewhat wary of changes in shipping lanes.

“We’re looking to improve the science, and get the best handle we can on what the abundance, distribution and behavior of these animals are so we can develop the best management strategy,” said T.L. Garrett, vice president of the Pacific Merchant Shipping Assn., a trade group that represents ocean carriers. “We don’t have adequate data to make those kinds of management decisions yet.”

Garrett said he was not surprised by the report’s findings that whales and ships intersect at certain times, given what is known about the species’ wide patterns of movement. The association supports efforts to develop real-time tracking of ships and whales, as is done for the right whale on the Atlantic Coast.

Garrett cautioned that changes to shipping lanes could have unintended consequences for shipping and other marine life.


DeAngelis agreed: “You wouldn’t want to put something in place that would be beneficial to the blue whales but then might be detrimental to humpback whales or fin whales — or ocean users.”

Researchers, regulators, shippers and others are planning to meet in the fall to discuss the latest data, DeAngelis and Irvine said.

Follow Geoffrey on Twitter @LATsciguy.