The biggest problem when using your drone for fishing is the risk of crashing into the water which could turn out to be a very costly accident! We’ve recently seen a fantastic innovation from Rutgers University in the US who have developed a drone that works just as well underwater as it does in the air. Their indented uses include using it for examining bridges/piers without having to send an engineer/diver down to review parts that may need repair. Once the prototype is a little more robust and can it can handle waves this would technology would be perfect for a sea fishing drone.
Take a look at this rather impressive video they made.