You're confusing diversity with abundance. Sure, there are lots of species out there that have not been described, but they are not described because they are rare, and the probability of encountering them is low. Commercially exploitable fisheries must be large, concentrated, and relatively easy to find - otherwise the cost of finding and harvesting can exceed the value of the fish. A lot of time and money has gone into searching for exploitable fisheries, and they've pretty much all been found and exploited.
Slashdot Mirror
You're confusing diversity with abundance. Sure, there are lots of species out there that have not been described, but they are not described because they are rare, and the probability of encountering them is low. Commercially exploitable fisheries must be large, concentrated, and relatively easy to find - otherwise the cost of finding and harvesting can exceed the value of the fish. A lot of time and money has gone into searching for exploitable fisheries, and they've pretty much all been found and exploited.