Some sea lions have had trouble with viruses. But as with people, sea lions are more susceptible to viruses if they're already not in top shape. Studies back in the 1980s indicated that Alaska's sea lions were showing signs of being nutritionally stressed. And there is the matter of nets. This has been a cause of accidental death for many thousands of sea creatures.
Fishermen are concerned with developing safer means of fishing and safe disposal of old nets.
Safer fishing methods will help protect the sea lions and other creatures of the sea who enrich our lives with their wonderous ways. And finally there is the human population that continues to increase, and the Steller sea lion population continues to decrease. Having more and more people in the world puts pressure on the fishing industry to catch more and more fish. This in turn puts pressure on the sea lions and other forms of marine life who look to the ocean for their food. To protect marine life we may find we need to share the bounty of the oceans.