Last winter I was kayaking on the Columbia River and when I came to a jetty I had to go around, I could see a couple of sea lions were messing around near the outboard end of the jetty. Not wanting to get too close to them, I decided to give them at least a hundred yards, so I headed out further into the river. When I thought I was far enough away, I turned downstream to round the jetty. At that point, the water all around me erupted with sea lions. I didn't have time to count them, but it seemed like there were at least a hundred of them and they were being pretty clear that I was either an object of intense curiosity for them, or I was not welcome in that particular area. I allowed that the latter seemed most plausible by their actions. Kayaks don't generally get on a plane, except when surfing, but I believe mine was close to a plane on my way back to shallower water where the lions don't usually go.
Anyone who thinks that sea lions are nice cuddly and harmless, probably hasn't had a close encounter with these massive (up to 3000 lbs.) creatures.