My brother has caught several sturgeon in the 100 pound range over the years in S.F. Bay.
They are the ugliest thing I've ever seen but the meat and Black Caviar are to die for!
One good roe laden female is worth BIG bucks and a number of men went to prison for taking spoonbill for the eggs from other states and without proper permits,etc.
There is just too much money to be made with sturgeon or spoonbill cavier for some folk to stay legal.
John,the poacher theory could easily hold water.Gill nets or snag lines placed under the surface would work for the fish and sturgeon roe is worth even more than spoonbill.
To keep line thieves from running my legal setlines,I often set them under the surface and free dive my lines so I don't have to drag them up and handle the weight.A poacher can do the same and keep things hidden but if he sees a warden coming just dump the fish in the water and a warden would have to have an idea to drag the right area for his lines.
I stay legal whatever I'm harvesting because I like to sleep well and when a warden pulls up at my house,I know it's for a friendly visit.:)