After reading the heartbreaking article about the demise of so many sea lion pups, I'd like to state what to me is an obvious cause of this "baffling" event.
We are turning our oceans into toxic septic tanks filled with human waste and industrial pollutants, also known as poison. In a futile effort to feed an unsustainable global population growth, we are stripping the oceans of life, leaving dwindling fish populations that can't sustain the basic needs of the seals. Of course, this nearsighted destruction of the Earth's oceans is affecting all of its inhabitants.
To call this baffling implies that the cause is mysterious and needs to be looked for; instead, there's an obvious solution that simply needs to be looked at.