well. Usuall when i play i noticed that the Strech and the white Admiral spwarn consecutively.Try checking first then if not there save the game (not in the mansion) other Safe House probably.and check again.
Common now.
Sharks are not a new thing in.
Sharks,Turtules asn Jelly fish are common creatures seen when you are wandering in boat.
But i noticed the are Kinda Empty.
Means you cant touch then and you pass through them.