The California population of blue whale, the world’s largest animal, and one of the most endangered, has leveled off while the numbers of other whales species continue to grow.
That’s perfectly natural, according to researchers at the University of Washington who studied the 2,200-strong blue whale population off the California coast.
Not only is it natural, but it can be considered a success story. The 100-foot whale was hunted to near extinction before receiving worldwide protection in 1966. When University of Washington scientists created a model of the species’ California habitat, they found it has reached 97 percent of capacity to support the huge creatures. In other words, the blue whale population has just about maxed out.
“Think of a perfectly nice open area, and seed it with a few individuals, who start to multiply,” said Trevor Branch, assistant professor of aquatic and fishery sciences at the University of Washington. “Eventually they’ll run out of food or resources, and they’ll slow down their increase and reach a stable level—which is what is happening with the whales.”
Branch and a doctoral student, Cole Monnahan, also looked into the effect on the population of collisions with ships, the leading cause of death of California blue whales. Between 1988 and 2012, there were 100 documented ship strikes along the California coast. Biologists say the actual number is likely higher, as ships often don’t know they’ve hit a whale.
“The most risky area for blue whales is the Santa Barbara Channel, where shipping lanes intersect with common feeding areas, leading to an average of 1.8 blue whale strikes reported per year in 2005–2010,” the scientists wrote in a study published Friday in the journal Marine Mammal Science.
Branch and Monnahan wanted to know if ship strikes were having a significant impact on the population of California blue whales, so they modeled the strike information with the population data. They found that 11 times more ships would have to cross whales’ path before the number of likely deaths would pose a threat to the species’ survival.
They stress that their findings does not mean restrictions on ships crossing the blue whale’s habitat should be relaxed. Other studies have found that shipping lanes near San Francisco and Los Angeles cross key blue whale feeding grounds. In recent years, regulators and shipping companies have altered shipping routes in an effort to avoid whale collisions.
“Our feeling is that there should be no strikes, and shipping lanes should be moved out of the way of whales if it’s possible to do so at a low cost,” said Branch. The findings have other implications: The researchers estimate that there are 11 blue whale deaths each year due to ships, and the U.S. government only allows for 3.1 fatalities.
The species faces other threats, such as pollution. But overall, the outlook is good for California’s blue whales. “Of all the whale populations in the world, very few have ever recovered to carrying capacity,” said Branch. “This is a good-news story: You stop whaling and the whales recover.”