No, not commercial net fishing that literally empty entire regions of fish, but recreational net fishing. Or crab fishing or trapping.
I think now this game have essentially covered almost every single part there is in fishing that requires a rod and reel besides fly fishing, so now I think perhaps RF4 try out some other fishing methods for the sake of diversity.
Net fishing would require extensive knowledge of the waterbody and very skillful placement of the net, and, depending on how you plan to net-fish, the bait. Some net fishing involves luring the fish close and casting the net almost like how you would cast a rod, others require you set the net beforehand and bait it, others would have you set the net and scare the fish into the net by throwing rocks etc. In fact, I have seen rigs that have specially designed nets attached at the end of a feeder for ground bait coupled with a float. It gains a bad reputation for emptying entire areas of fish but rest assured this is only limited to commercial fishing. Recreational net fishing requires as much skill for an experience angler would need for his rod.
Crab fishing and trapping (mussels and clams) are quite similar to net fishing, but they are a LOT less dynamic. You will not get any indicators of crabs and mussels sneaking into these traps and trying to munch the bagged bait in the middle. Crabs and mussels, as omnivores, eat the most intriguing variety of I have every observed in omnivores. From bait selection, I have seen people hook from sausages to chicken breast to rotten fish to cucumbers to canned crab and the wildest stuff imaginable and stills somehow catch a batch of these curious creatures. Sometimes fish and other sea-dwellers may wander inside there, but they are rare. Crab/trap fishing would require an extensive knowledge of waterbodies and underwater structure. It would also require knowledge of the tide, wind, moon (tide) and much more to have a successful haul. One might set out tens of traps one night only to find in utter dismay they next day that the low tide has actually fell beneath the traps. Nothing but only bait.
Yes, I will have people say to me, "tens of traps will ruin the experience" I know it will, and there is a solution to this: Trap/Net limits. Just like for rods. This way, you won't have players hurling thousands of 'em at once.
Well, thats it, just some suggestions to spice up this game, more diversity is, I suppose, always welcome.