Researchers believe that California blue whale numbers have recovered to a point that is sustainable, nearing historic highs from decades ago. Scientists are saying that this is so far the only population of blue whales that have rebounded from whaling ravages of the previous centuries.
A blue whale can grow to 108 feet (33 meters) in length and weigh up to 209 tons (190 tonnes), making them the largest animals on the planet and weighing about twice as much as the largest known dinosaurs.
Despite the comeback, scientists warn that the blue whales are still being struck by ships at twice the U.S. limit for population growth sustainability, say the study’s authors. Conservation groups estimate that at least eleven blue whales are struck annually off the United States’ west coast. The U.S. Marine Mammal Protection Act gives the “potential biological removal” level for such strikes at just 3.1.
The Telegraph reports that the report on blue whale numbers, published from research at the University of Washington, shows that blue whale numbers are at 97 percent of their known peak. About 2,200 blue whales are said to be off the California coastline.
Blue whale numbers had plummeted to about 951 individuals in 1931 due to commercial whaling. Whaling was banned in 1966 by the U.S. and several other countries. Some illegal whaling continued after that, but eventually ceased. Scientists believe that had commercial whaling not ceased, the blue whale numbers may have dwindled to extinction.
The University of Washington paper cites a separate paper published earlier this year, as reported in The Guardian, showing that between 1905 and 1971, when commercial whaling off the U.S. coast ended, about 3,400 blue whales were caught. Some of those numbers come from now-declassified Russian whaling archives. The scientists of this new, positive report are cautionary, however.
“Our findings aren’t meant to deprive California blue whales of protections that they need going forward.”
The researchers remind readers that the blue whale numbers are better because of the ban on whaling and the monitoring that followed.
Measuring the blue whale numbers was not as cut-and-dried as it may seem. The BBC reports that the scientists had to first find the dividing line between the California blue whales and other species in terms of where they are in the water. New understandings of whale calls and whistling gave them that capability, allowing them to more accurately count current populations and compare that to whaling records.
In order to reduce the number of whales lost to accidental collisions by shipping, a government program now pays ships to slow down their pace in the waters most heavily populated by blue whale numbers. The plan may be working, reports the LA Times.