In many European countries spearfishing with scuba equipment is forbiden by the law, as being unfair to fishes (chances are not equal). You can only spearfish as a freediver.
I live in the middle of the United States, and for 40 years have been a spear fisherman, At one time the Underwater Society ran spearfishing championships for fresh water, and the most common target was Carp. Carp are non native to America, and were brought here from Europe where they were popular in clear rocky waters. In the U. S. they have spread through most of our man made lakes with mud bottom and have outgrown and eaten the eggs and young of our game fish.
In the Southern U. S. lakes are poisoned regularly to kill off the carp, and usually very few game fish. A 20 or 30 pound carp will push off the 2 or 3 pound fish guarding the nest and eat all the eggs, year after year.
For many years many of the best spear fishermen could kill 30 to 50 carp in a four hour contest. Missouri and Oklahoma divers dominated the championships for many years. An adjoining state, Arkansas, had fisheries biologists study the ability of the best spear fishermen, and the best hook and line fishermen, and while the divers could take better, larger fish, divers could never take as many game fish. Game fish don't crowd up like the carp do when spawning.
The Arkansas fisheries biologists have introduced new game species and attract fishermen from many miles away, their efforts have made the fishing more plentiful and larger fish than competing states fishing. Bigger and more black bass, walleye, catfish and stripers. Banning some things can barely keep it going. . . Spending money to improve the fishery works better. Arkansas sells lots of out of state fishing licenses because they have studied what works and what doesn't work. Big fish attract trophy hunting Illinois fishermen to catch bigger walleye in Arkansas lakes than they can find in their local lakes where the walleye were native.
Spear fishermen didn't make fishing better, but our money from out of state fishing licenses have supported good people who have created limits that increase the size and number of fish. A long history of competing national boundaries may make one country unable to improve things. But to improve all the fishing, taking selected fish is always better than taking all the fish and all the bait, and damaging cover. . . like netting and commercial fishing has done.