This addon silences Riggle Bassbait's announcement of each "first winner" during the Stranglethorn Fishing Tournament. It also replaces the chat yell with a sonar ping and a message showing how many times you've seen the message since your last interface reload.
You can disable the sonar ping by commenting out or deleting line 23 of QuietFishingTournament.lua. You can also change the sound played to something else by changing the ID number on that same line. A list of sounds and IDs can be found on Wowhead.
Due to how this particular addon works, the zip file contains a complete folder structure. To install, you'll need to extract the zip to the top level of your WoW install folder. Feel free to poke around the zip to see that nothing malicious is going on. It's just important that the sound files end up in the proper place.
To completely remove this addon, you will need to delete the "Sound\Creature\Riggle_Bassbait" folder that is placed in your WoW folder, in addition to the "QuietFishingTournament" folder. Otherwise, the Riggle will remain audibly mute, while continuing to yell in your chat log.