The amount of Malbatross fish shoals is too random

[CossonWool]

Currently the black catfish shoals (Malbatross shoals marked on the map) are randomly spawned in worlds as part of world generation. I don't know if there's a guaranteed minimum or maximum amount, and if there is then that minimum and maximum is too extreme. I've had worlds worlds with only 4 and others with 23; over a 5x difference. If the shoals are meant to be rare then 23 could be considered high, and unless they're meant to be very rare then 4 is too low.

If the shoals were unimportant this wouldn't matter, but Malbatross hunting and shoal fishing are both fun parts of the game that are too important for this level of randomisation.

Not sure if shoals generate based off world seed, but if they do then here's a couple seeds (Windows 10):
World with 23 shoals: 1574123558
World with 4 shoals: 1574122707