I use to work in guntersville ala and crews with diving bells would come to the lake and harvest huge mussels and export the mother of pearl to japan. $4000 a day on a good day but they were limited to only a few days a year.
Horace, when I was a youngun growing up between the HWY 280 bridge and the forks of the rivers in Southern Wheeler County, those were numerous, along with the Altamaha Spike mussel. They looked like that but would have a spike on the shell up to an inch long or so. I wished I had saved a couple of those spikes now. Haven`t seen one in a long time.
I have seen them as large as dinner plates ( not an exaggeration ), in the White River. There use to be pretty good money in gathering mussels. Like someone else said, 3 to 4 thousand in a couple days was not uncommon. but it took another day of shucking and bagging and another day to drive to Memphis and back to deliver to the buyer. My cousins were pretty involved in it.
There are some huge ones on the Red River up here. We were wading the river on day and I felt a smaller one on the bottom. Walked over to the boat we were pulling behind us, got a knife popped it open and ate it. It weren't no raw oyster, but it weren't bad. I would not sit down and eat a dozen of them.