Seafood can be a big money proposition. On thing about seafood is that (the growth of "farming" notwithstanding, there are many fish, crabs, shellfish that CAN'T be farmed) is that when a given species is overfished, they become rarer, but demand stays the same, so the price per unit goes up, meaning people are even MORE motivated to go after it, even though it may take longer to find the few that are left.
So, on pretty much every coast, to legally harvest a lot of things in ANY quantity at all, you need a "commercial license." And to prevent overfishing, these licenses are often now either 1) very expensive, or 2) limited in overall number so that it's next to impossible for someone new to get one, or both.
So you'll see poaching develop.
And it's not really "fishing" in the case of lobsters and abalone, it's going down and physically picking them up.