Attacks by pirates and the number of ship seizures have been on the rise since March, a senior Chinese naval commander has said.

Navy doctors examine Yi Jixiao, a crew-member of the Chinese fi shing trawler Long Fa on Tuesday. China's fifth escort fl otilla in the Gulf of Aden sent staff to the Long Fa upon receiving an emergency call for medical assistance. [China Daily]

In March alone, 20 ships were hijacked in as many as 51 pirate attacks in the Gulf of Aden and waters off Somalia, Zhang Wendan, senior colonel and deputy chief of staff of the South Sea Fleet, said.

Zhang, who is also the commander of China's fifth escort flotilla sent to the Gulf of Aden, said pirates are using new tactics, as international organizations are making more efforts to ward off the threat from piracy, and commercial shippers have strengthened defenses.

The pirates' reach has also increased, and their operations have extended to areas far from Somali waters.

Earlier, pirate activity was mainly contained to within 50 to 60 nautical miles.

However, the attackers have now expanded their reach to as far as southeastern Tanzania, the waters near Madagascar and almost the whole northwestern Indian Ocean.

The pirates have also diversified their targets. Most of their traditional targets were low-speed commercial ships. But now, they are choosing to attack small sailboats and fishing vessels, which are being seen as easy prey.

Large oil tankers, as well as bulk carriers, are also becoming more favored targets due to the high ransoms that they fetch, Zhang said.

The pirates have also got better at concealing their intentions.

Tripwires are used to trap the target ship's propellers, giving the pirates a chance to get onboard.

Pirates also submerge their weapons, ladders and tools into the water to avoid detection by escort vessels, or use common fishing and smuggler boats as cover.

The pirates have also resorted to more violent tactics, Zhang said, adding China's escort fleet is working hard to stay one step ahead of the pirates.

Zhang also proposed that counter-piracy information be shared with other countries' escort fleets to help improve commercial ships' defensive capability.