According to some recent news sources, Somali piracy seems to have scared away foreign fishing vessels and have led to increased fish catches off northern Kenya.
Some scientists working in the region disagree with the piracy hypothesis, though, saying the increased catches have more to do with environmental changes associated with warmer waters that shifted to East Africa around the time of the reported catches.
Even if the piracy story is not true, it should be true. During WWII, when fishing boats and their crews were needed for the military rather than seafood markets, fishing after the war was over also showed improvements. That not mean piracy should be a conservation goal. Nor should war. However, if we left the ocean alone, fisheries would likely rebound.
Somalia is a poor country with government in shambles and practically no navy. Foreign fishing vessels have been fishing illegally in their waters, taking away much needed food from the rightful owners. There is not one group at work here and generalization should be scarce.
Of course, the newsworthy event is when pirates capture a cargo vessel (and some crew) which may bring in a lot of cash for ammo. You of course didn't hear when when they chasing away "fishstroyers". I wouldn't go as far as calling them pirates.
Of course, you can always try and prove me wrong.