Dogs - Shark Issues?

[CptFB]

My wife and I have a Golden Retriever "Tucker" that loves the water. Today, we live inland and our boat time with Tucker has been on a fresh water lake. It is a full time job to keep Tucker in the boat underway (we have a 20' bowrider now) and as soon as we are at anchor....splash! His favorite activity is to jump off the bow of the boat (his "high dive"), swim aft, board and repeat.

Our goal is to be cruising full time in the next few years (still undecided on boat type, but are leaning towards a catamaran). Though we are aware that Tucker will need additional training before his full time life at sea, he will be part of the crew. Given that he is a true water dog, we know we couldn't and wouldn't prevent him from swimming once the boat is moored/anchored. One of our concerns is losing him to a shark.

We are curious if our fear is justified. Should we be worried? Does anyone have an experience or story they could share?

Thanks in advance for any insight. We love our boy and want him to be safe.