A federal ban on caviar imports from the former Soviet Union could end up endangering pallid sturgeons in the Missouri and Mississippi Rivers. Shovelnose sturgeons are legal for amateur and commercial fishermen to take, but the pallid is endangered. Commercial anglers say they can tell the difference, and they throw the pallid sturgeons back. Biologists say amateurs might have more trouble and could end keeping the endangered one. A belly full of roe could net and angler $200 worth of caviar.