The figures collected by the IMB (international Maritime Bureau), are a vital barometer of pirate activity and there is a good graphic:
Worldwide Incidents 2013: 100 reported incidents including four hijackings.

Somali related incidents 2013: Six reported incidents including one hijacking.

Current crew / vessels held by Somali pirates: hostages - 71 / vessels - 5

Nigeria related incidents 2013: 19 reported incidents including one hijacking.
Link:http://www.icc-ccs.org.uk/piracy-rep...cynewsafigures