Neither have I. They must go after them on occasion, though, and I'll tell you why. There is a long dock down at the river where seagulls and cormorants love to congregate to rest, relax and socialize. An osprey or hawk can fly through the area and it doesn't bother them in the least, but if an eagle flies through, they will all take to the air. The only reason I can think of for doing that is because an eagle must occasionally attack seagulls. Taking to flight allows them more options for evasion. I use this known behavior as a cue to alert me when an eagle flies into the area.
Seagulls flying out of respect for the eagle.