The penalties for poaching have to be extremely severe so as to outweigh the risk. Whether it is prison time, destroying boats, or even deadly force (no, I am not advocating it). There has to be a huge disincentive to even risk the endeavor.
One of the things I remember from my soc101 professor was that for a criminal justice system it needed to have punishment be swift, severe, and sure. I think the first two criteria are easy in a practical sense, but the third criteria is more difficult. The seas are large, so catching poachers is no small task, given the limited resources of some of those countries.