8th September 2014 Blue whales in coastal California recover to Blue whales off the California coast have recovered to near historical population levels, now numbering about 2,200.
At 30 metres (98 ft) in length and reaching 190 tons or more in weight, the blue whale is the largest existing animal and the heaviest that ever existed – twice the weight of the largest known dinosaur. Blue whales were abundant in nearly all oceans on Earth until the early 20th century. For more than a hundred years they were hunted almost to extinction by whalers, until protected by the international community in 1966. In coastal California waters, blue whale numbers have now rebounded to near historic levels, according to a study published in Marine Mammal Science – and while the number of these animals being struck by ships is higher than U.S. limits, such strikes do not immediately threaten that recovery. This is the only population of blue whales in the world known to have recovered from whaling. "The recovery of California blue whales from whaling demonstrates the ability of blue whale populations to rebuild under careful management and conservation measures," says Cole Monnahan, from the University of Washington, lead author of the study. California blue whales are at their most visible while feeding 20 to 30 miles off the California coast, but are actually found along the eastern side of the Pacific Ocean from the equator up into the Gulf of Alaska. Their numbers in this region are now estimated at 2,200 – which is likely 97 percent of the historical level, according to the model the researchers used.
There are likely at least 11 blue whales struck by ships every year along the West Coast, which is above the "potential biological removal" of 3.1 whales per year allowed by the U.S. Marine Mammal Protection Act. However, the new findings show there could be an 11-fold increase in vessels before there is a 50 percent chance that the population will drop below what is considered "depleted" by regulators. "Even accepting our results that the current level of ship strikes is not going to cause overall population declines, there is still going to be ongoing concern that we don't want these whales killed by ships," said co-author Trevor Branch, assistant professor of aquatic and fishery sciences. The population returning to its historical level explains the slowdown in population growth, noted in recent years, better than the idea of ship strikes, according to the scientists. With no other readily apparent human-caused factor, whale numbers are reaching their habitat limit – something called the carrying capacity.
"We think the California population has reached the capacity of what the system can take as far as blue whales," said Branch. "Our findings aren't meant to deprive California blue whales of protections that they need going forward," Monnahan said. "California blue whales are recovering because we took actions to stop catches and start monitoring. If we hadn't, the population might have been pushed to near extinction – an unfortunate fate suffered by other blue whale populations." "It's a conservation success story," Monnahan concluded.
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