As a retired Special Forces, Ranger
officer with extensive experience working in the intelligence field, I can offer a relatively simple solution to the "pirate" problem which is compatible with international conventions relating to operation/use of international waters.
1) That the Somali government
does not, for practical purposes, operate a maritime navy
2) That Somali fisherman do ply international waters in furtherance of their fishing
3) That Somali pirates utilize, at a minimum, rifles in pursuit of their prey (but more often automatic weapons, rifle propelled grenades and other sophisticated munitions).
4) That the EU and United States, as well as other nation-states, have established a maritime presence in the Red Sea.
5) That Keyhole 12 (and other reconaissance satellites) assets are available to monitor
the comings and goings of vessels from the Somali shoreline.
Then armed with intelligence of the location of those vessels that depart the Somali coast, their bearing and speed, it would be relatively easy to:
1) First intercept those vessels with air assets to confirm their identity.
2) Intercept the vessels with seaborne/rotary aviation assets to board and search the vessels for evidence of weapons (not normally used in fishing
If weapons are found, the vessel is consequently identified as a pirate vessel (since Somalia
does not operate a navy), the individuals and weapons are seized, the weapons and vessel are sunk, and the individuals are returned to the Somali coast by rotary winged assets at a location not subject to interdiction by Somali warlords or other armed interventionists.
This approach would make it non-profitable for the pirates to continue plying their trade
as their means of interdicting legitimate sea traffic would be "scrubbed" from the area and consequently diminish, yet the nations involved in "policing" the area do not bear the expense of incarcerating or prosecuting the criminal activities of the "pirates". It does not depend on catching the "pirates" in the act, but rather uses the instrumentalities of such crime, i.e. the weapons, to infer illegal status to the vessel and its occupants and thus allowing for the destruction (sinking) of the instrumentalities.