If you look at that map, Nigeria seems far more active 2013 then Somalia. Too bad it's only for 2013.
"Al Shabab has been terrific at stamping out piracy from its ports, due to its harsh interpretation of Shariah and the personal animus between profit-seeking pirates and Islamist militants.
[...]
"Now that Al Shabab is in retreat, the emerging power vacuum in Somalia’s southern ports may lead to ‘sweet-spot’ conditions for pirates to resurface."