Whales assemble in California's busy shipping lanes, increasing potential for collisions. Some 2,500 of estimated worldwide population of 10,000 found off West Coast.
A new study in the journal Plos One has revealed blue whales assemble for long periods in the busy shipping lanes off California, raising concerns about collisions between vessels and the endangered cetaceans.
“It’s an unhappy coincidence,” said study leader Ladd Irvine, a marine mammal ecologist at Oregon State University. “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 colleagues utilized satellites to track 171 tagged blue whales over 15 years, producing the most detailed maps to date of feeding zones. The biggest overlap between
blue whales and ships occur from July to October near the western Channel Islands off Santa Barbara. Somewhat smaller overlaps occur near the Gulf of the Farallones off San Francisco and at the northern edge of Cape Mendocino.
Tags and satellites
With tags and satellites, Irvine’s group recorded individual whales over 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. The study's conclusions are at odds with previous research suggesting shifts in shipping lanes would not help the whales due to their wide dispersal. That research was based on whale sightings, which are more rudimentary than the new study’s tracking methods.
In 2012, the International Maritime Organization agreed to divert southbound ships more than a mile 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 upwellings in deep-sea currents create dense krill schools, the whales’ primary food source.
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.
—Ladd Irvine, marine mammal ecologist at Oregon State University
However, the changes took years to implement, and any new dialogue about further shifts is expected to some time. The shipping industry, which has supported additional research on whale populations and behaviour, is somewhat wary of changes in shipping lanes.
The largest animals on Earth, blue whales can grow to more than 30m long and weigh 150 tons. About 2,500 of the estimated worldwide population of 10,000 congregate in the waters off the West Coast.