Aceh has long been reputed to be the home of some of the pirate bands and much of the coastal area (and harbors) there are no more-limiting pirate havens and bases of operation. (Update: Interesting post here)
It could also be the pirates have turned to ripping off aid supplies and haven't felt the need to work as hard at their sea-going trade. We'll have to watch the trend lines.
Update: On the other hand, the latest ICC-CCS (International Chamber of Commerce - Commercial Crime Service) Piracy Report reports:
23.01.2005 at 0340 LT at Panjang port, Indonesia.Here's a map with arrows pointing to the Aceh area and to what I gather is the Panjang area.
Three robbers armed with long knives boarded a tanker at berth. D/O raised alarm and crew mustered. Robbers jumped overboard and escaped empty handed in a speedboat.