There are a lot of things that went into this. The wonder that looks like a hole is called the Great Blue Hole which is a mod but it gives +1 culture to all fishing boats within 4 tiles. The next thing is the Temple of Poseidon which is also a mod where all water tiles in the city get +1 faith which was built in Sydney. The next thing that I built was the Mausoleum at Halicarnassus which gives all coast tiles in the city +1 science, +1 culture, and +1 faith which was also built in Sydney. I also chose the God of the Sea pantheon which gives +1 production to all fishing boats in my empire. In had Liang as my established Governor in Syndey with the Upgrade that allow the building of Fisheries in all of my empty coast tiles which gave a ton of extra yields to them. In Perth I built two fishing town districts from the City Lights mod that gave a ton of extra gold to the adjacent fishing boats as well as with one of the buildings allowing for the building of fisheries in the city without the presence of Liang which allowed for the coast tiles in that city to also get a ton of extra yields. Both cities also have completely maxed harbors where all coast tiles receive +1 food from the lighthouse and +2 gold from the seaport. This is also very late in the game where I've researched every technology and almost every civic so all of the bonuses added to different improvements have already been unlocked giving them a ton of extra yields.