I was on station off the coast of Somalia for two months back in 2006. Thing is, this is a ridiculous amount of waterspace to patrol and enforce. One option for dealing with it would be to assign merchant ships into convoys and provide one or two picket ships at the front and back of the formation to provide cover. These ships would come from the international Task Force 150, which has been operating in that area for some time. The neat thing about TF150 is that it truly is a multi-national force. I was on the USS Barry, an Arleigh Burke-class destroyer, and during the time we were CHOP'ed (under control) of TF 150 we worked and took orders from the British at one point and the Germans at another. Now, obviously if we received emergent tasking or 5th Fleet countermanded a TF150 order, we'd go with that. Anyway, back to the pirates...
Here's a couple options I see for dealing with this and the negative sides of each:
1. Group merchant ships traversing the east coast of Africa into formations have have picket ships from TF 150 riding shotgun. No pirate in the world would be dumb enough to try anything then. At least I hope not.
This would be very expensive in diesel fuel for the warships riding shotgun, much more so than I believe any gov't would be willing to spend for an indefinite amount of time. On top of that it would be a logistic nightmare - coordinating multiple shipping companies to have their ships wait on station at their last port of call until enough were ready for the formation. Don't see this one happening.
2. Have SEALs/VBSS boarding teams on hot standby ready to covertly insert and re-take whatever ship the pirates had.
The interior of most Group III merchants is a tactical nightmare. You'd have to expect the pirates to have a little more familiarity with the interior as well, so they would have the advantage. The SEALs and VBSS could get the job done, but it would most likely be a bloodbath on both sides, plus the pirates might decide to get into the hostage executing business. This is probably a bad option and would not be undertaken unless they threatened something drastic, like scuttling the oil tanker or if threatening to execute hostages.
3. Have shipping companies pay for armed security details on ships that are traversing the East Coast of Africa.
While not directly addressing the pirate's operations, this is probably the best option for these companies. The berthing and feeding of the details would be an issue, plus the added expense in hiring them. The cost of this would probably be less than the ransom they are paying to these mooks. Plus, insurance on shipments going through the area could offer a discount on their already astronomical fees if the ship had an embarked security detail.
As far as tracking them, as long as they continue to use small craft it doesn't give us much to go on as far as ELINT. Their "mother" craft most likely have some kind of search radar, because the latest seizure was well out into open waters and they would have needed it to locate their target in total darkness or inclement weather. This isn't a guarantee though. They could be navigating from experience and charts and simply sighting their targets visually.
I think what is needed is for us to work with whatever NGO's are friendly to us out there. (No doubt the intel services of every country they've stung are already working this angle.) Of course if that's dry, and we can tie their activity to a specific area or facility...well, then it's RGM-109 Tomahawk time, baby.