Clobbered. A blue
whale's carcass floats off California. A necropsy showed the cetacean died from
a ship
The 171 tracked whales are members of what’s known as the
eastern North Pacific population, which comprises about 2500 individuals.
(There are about 10,000 blue whales worldwide.) “It’s an amazing and
unprecedented sample size; there’s nothing like it for any other species of
whale,” says Phillip Clapham, a cetacean biologist at the National Marine Mammal
Laboratory in Seattle, Washington, who was not involved in the study.
The study began in 1993 after Bruce Mate, a cetacean
biologist at Oregon State University’s Marine Mammal Institute (MMI) in
Newport, developed methods for attaching satellite tags to the backs of large
baleen whales. The researchers approach a whale in a rigid inflatable boat and
then deploy a tag designed to implant in cetacean skin from modified crossbows
or compressed air guns, aiming for an area near the animal’s dorsal fin. Of
these baleen whales, the blues (Balaenoptera musculus) are the largest; indeed,
they’re the largest animal to ever live (even beating out the heftiest
dinosaurs), with some of the creatures measuring 30 meters in length and
weighing 170 metric tons. Yet despite their great size, little was known about
their range or movements. “Blue whales began showing up off California in the early
1990s,” says Ladd Irvine, a cetacean researcher also at MMI and the lead author
of the new study. “But we had no idea of where they came from or where they
went to breed, or even their numbers at that time.”
Mate, Irvine, and their colleagues began to fill in those
blanks by tagging blue whales found along the California coast and tracking
their movements. They were also curious about why there weren’t more blue
whales, because the populations of other species of baleen whales have
increased dramatically since the International Whaling Commission banned
industrial hunting of some whale species in 1966. “When compared to other large whales that
inhabit the same area, the blue whale population doesn’t appear to have
increased at a similar rate,” says Monica DeAngelis, a marine mammal biologist
at the National Oceanic and Atmospheric Association’s (NOAA’s) National Marine
Fisheries Service in Long Beach, California, who collaborated with the paper’s
authors on this project. Humpback whales in the North Pacific, for instance,
now number about 20,000, up from 1400 since the ban. To find out more about the blue whales’ movements, the
researchers programmed some of the tags to transmit location data either daily
or every other day; other whales were fitted with tags that transmitted every
day for the first 90 days, then switched to every other day until the tags’
batteries ran out. Tags implanted by crossbow lasted 58 days on average; those
deployed by the air gun method kept ticking an average of 85 days. One whale’s
tag continued beaming data for a remarkable 504-day period. The team’s analysis
of the tagged cetaceans’ movements, reported today in PLOS ONE, showed that
they faithfully return each summer to the rich, upwelling zones off Santa
Barbara and San Francisco that produce masses of krill, their main prey. But
these same areas are also crossed by major shipping lanes, with vessels
traveling to and from the busy ports of Los Angeles and San Francisco. “It’s an unhappy coincidence,” Irvine says.
Over a 2-week period in 2007, for example, at least three blue whales were
killed by ships striking them near California’s Channel Islands. (Two other
blue whale carcasses were spotted during the same 2 weeks, but the scientists
weren’t able to study them.) “That made everyone say, ‘Whoa,’ ” says Irvine,
who recalls seeing the injury to one of the dead whales. “It had a huge hematoma
from what was clearly a massive, blunt trauma.” The scientists don’t know how
many of the eastern North Pacific blue whales are being hit by ships. (“Some
vessels are so big they may not even know that they hit a whale,” Irvine says.)
And they still can’t say if such strikes are the most important factor keeping
the cetaceans’ population numbers low. “At a minimum, it’s not helping,” Irvine
says. And because the eastern North Pacific population is the best studied
stock of blue whales, scientists suspect that the whales are suffering
elsewhere from ship collisions. “The reality is … ship strikes are a global
threat to this species,” DeAngelis writes in an e-mail. Happily, there is a
model for improvement. In the Bay of Fundy on the Atlantic coast of North America,
lethal ship strikes posed a similar problem for right whales in the 1990s.
Then, 11 years ago, the maritime industry there moved one key shipping lane and
agreed to have ships enter and exit ports at slower speeds—which was especially
effective, Clapham says. “Speed restrictions give whales time to get out of the
way.” The changes reduced the likelihood of vessels striking the endangered
whales by about 80%.
In this case, the researchers say shipping lanes near the
Channel Islands and off San Francisco would need to be moved to end the
collisions. They recommend altering the routes through the Santa Barbara
Channel during the height of the whales’ feeding season, from July to October,
and closing the northern shipping lane to and from San Francisco Bay ports
between August and November. And although such changes are not easily made,
NOAA is taking a first step. It will be conducting a review—informed by this study—of
the especially busy shipping lanes off southern California and consulting with
the various stakeholders about a “plan that would be beneficial to everyone,”
Irvine says. After all, he points out, a ship hitting a whale that weighs as
much as 25 elephants isn’t good for the vessel, either. Tomado de envío de
sciencia
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