Is this normal? What does this beep tell me?
After a 15-20 minute ride to fishing spot, shut off motor & anchor. Every 15-20 minutes I hear a single very short beep.
?

Fishing, a man knows a serenity of soul and peace of mind that he finds in doing nothing else, and it makes no difference whether or not he catches anything. The mind of a true fisherman is not on petty subjects.