With Western navies focused on trying to quell Houthi militant attacks on merchant shipping in the Red Sea, Somali pirates are quietly showing signs of making a comeback.

In December, they hijacked their first ship in six years when the commodity carrier Ruen was boarded and taken to a port in the east African country, according to the International Maritime Bureau, a piracy watchdog. Figures from the European Union Naval Force show there have been further attempts since then, and this week the U.K. Navy issued an advisory to shipping cautioning that pirates are operating in the Indian Ocean.

For the maritime industry, the incidents are a chilling reminder of a period — a little over a decade ago — when Somali pirates menaced ships across swaths of the Indian Ocean. Back then, incidents included seizing the giant oil supertanker Sirius Star and the U.S.-flagged container ship Maersk Alabama. They led to what was viewed at the time as a controversial deployment of armed guards on board commercial ships.