It looks like your conviction may be eligible to vacate, based on the following exception for some fishing-regulation convictions related to treaty fishing rights:
Vacating records of conviction for misdemeanor and gross misdemeanor offenses as defined in RCW 9.96060(4)
This applies to you if your (or a deceased family member's) conviction was for violating a fishing regulation, and you (or your family member) are part of a tribe that had official treaty rights at the location and time where you were fishing.
When you are ready to begin the process, here are the next steps:
Read the local court rules or contact the clerk of the court where you will file your petition to find out if you need any additional records to be submitted with your petition.
Fill out the "Motion and Declaration for an Order Vacating Conviction – Treaty Indian Fishing Rights" form: Washington Court Forms - Form (CrRLJ CR 09.0500). You will also need a Tribe or Nation representative to sign the Tribal Status certification.
Make at least 3 copies of all paperwork.
Seek out more information from your County's court (see a directory here).