system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do commercial fishers know what they are going to catch?

They will seek out huge loads of one species and throw out the rest... but how do they hunt and track specific species?
gpt
Location, depth, bait, tools.

Certain fish are only in certain locations, so to fish a specific fish you must be in a specific location, this isn't necessarily the difference of Alaska vs Florida, but can be location where a certain environment or phenomenon is observed IE: where currents come together, or where certain food can be found said fish like.

Certain fish swim at certain depths, you fish as deep where the fish will be.

Certain fish are attracted by certain kinds of bait.

To catch specific fish you might use different methods or tools, something that is most effective for that kind of fish, it's not always just massive nets.