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Visit the sandy beaches of the West Coast, and there’s a good chance your would-be sunbathing spot is already occupied by a California sea lion. There are as many as 300,000 of these ear-flapped, whiskered, and very noisy marine mammals living in the U.S. alone—but their population hasn’t always been so robust. Hunting and pollution throughout the years meant that there were fewer than 90,000 animals by 1975. The Marine Mammal Protection Act, passed in 1972, is credited with spurring the full recovery of the California sea lion population.
But now that the sea lions are once again brushing up against their natural carrying capacity—or the number of individuals that their environment can support based on available food, habitat, and resources—and scientists who study the animals are starting to see some wacky changes. In a paper published on April 27 in Current Biology, ecologists at UC Santa Cruz and the Smithsonian Institution detailed one such discovery: As population size has grown, the males’ bones seem to be growing larger. Of the sea lions researchers studied between 1962 and 2008, the average male’s skull grew nearly 10 millimeters.
“Some research has shown that as marine mammal populations increase, competition for resources with other individuals and species will likely intensify, eventually resulting in less prey availability,” Ana Valenzuela Toro, the lead author of the new research and an ecology researcher at UC Santa Cruz, told The Daily Beast. She added that for harbor seals and other species of sea lions, these pressures have been found to lead to smaller, not bigger animals, which can hurt species survival in the long run.
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