An employee leaves a Dive charter boat and takes a copy of the boats client/customer list for emails

Since you don't mention it, I assume that you do not have a non-compete agreement with this former employee.  Even without one, however, a former employer is not allowed to use his former employer's trade secrets to compete with it.  Customer lists can be considered trade secrets, depending on the difficulty of obtaining the information on the list from public sources, the time/expense which went into compiling the customer list, and the efforts which went into keeping it secret.  If you believe that your customer list could be considered a trade secret, you can sue the diver seeking to enjoin him from using it and for the damages you've sustained due to his use of the trade secrets to now.  If you choose to sue, you should do so quickly, since the longer you wait the less chance you will have to convince the court that you are being irreparably harmed by the diver's use of the trade secrets, a necessary element to obtain a preliminary injunction.