Here in Michigan this type of commercial fishing is not allowed. Gill nets are allowed in the Great Lakes, with a commercial license. No commercial fishing on inland waters. I would think it could be detrimental to smaller lakes, but large bodies of water should be able to withstand this type of fishing pressure.
One poster says it is hard to make $30 to $40 a day and another says he makes $300 to $500 a week. How is one paid for the fish? By the pound? How many pounds would one have to sell to make $500 in a week?