WOW! In 25 years of SCUBA diving off the coast of Northern California (and hundreds of SCUBA dives) I can only remember 2 that I did without a spear gun. One out in front of the Monterey Bay Aquarium (didn't think we would be looked at favorably be the tourists hauling fish back into the inflatable) and the other up at Mendocino after a free dive for abalone. My buddy and I did a tank dive to explore more areas to dive for abs.
Did 2 trips to the Caribbean, Grand Cayman and Bonaire, but tourists were prohibited from taking any game ... and there were some BIG BUGS to be had, but it was a no no.
Guess it is illegal to spear fish for sturgeon in Ft. Peck.
I think the only 2 places it is legal to underwater spear fish in ND is DL and Sak.