While I worked on a primitive fishing gorge mod for the game, I had the opportunity to ask Sami some questions.
Fishing rods and nets "can" target multiple fish of varied size.
Rocks (clubs), spears/javalins and (maybe) trident all target a single large fish.
Do you know, or have you experienced any difference between different objects of the same quality that aren't nets or fishing rods?
I do not know, things like rocks and stones as you know are decent quality 50~60%. a better quality jav etc. may more quickly catch a fish 'If" a fish is there to be caught. Though the fishing timer runs pretty fast for me to do compares.
As mentioned I did make a gorge, which was a rock in game, of high quality and it did seem to catch fish faster than with a rock. Coud just be my perception, not based on facts.
As Privateer says, I've also always been able to catch survivable amount of fish just by using a rock, however that have only been with Islander characters I've been playing with, who starts with a fairly high skill of fishing.
My best tip would be, to always make sure you perform rituals and sacrifices, when living off of fishing. The spirits certainly rewards the people who don't get too greedy.