Cormorants? The most effective thing with them is Alka Seltzer. Split an anchove or grunion, tuck a piece of Alka Seltzer in it and chuck it to them. For some reason they can't burp so their gullet explodes. California has a fit if they catch you. I see it as a win win. No more cormorant, and the sharks get a free meal. One of my buddies was quite adept at turning seagulls inside out. He'd cast some anchove out, and just let the gull run with it until he couldn't keep all the line in the air. Close the bail and yank as hard as he could. Funny seeing the gull do an abrupt 180 and unload his innards. You can chuck pieces of anchove in the air until you get a cloud of gulls over you. then chuck a piece of Alka Seltzer.
To those of you who haven't dealt with comorants or the gulls leaving 2 or 3 inches of hard as rock poop on your boat, or getting a staph infection on your knuckles from scraping the poop. This might sound cruel. Naw it's just frustration..........