Piracy has long been a problem in the vast, resource-rich body of water stretching from Senegal to Angola, where most victims kidnapped by pirates are sailors working on ships.

Crimes used to occur closer to the coast, but shapeshifting pirates have moved further afield to evade authorities, complicating an already difficult game of cat-and-mouse for authorities.

"States and navies have taken measures to limit attacks near the coast. That pushes pirates to change their modes of attack," said Pascaline Odoubourou, founder and editor-in-chief of the Maritimafrica website.

Oumar Wade, chief of staff of Senegal's navy, told AFP that pirates have struck more than 100 nautical miles (185 kilometres) from the Gulf of Guinea coast since 2020.

But it is only recently that international action against piracy has been mobilised.

"The rising power of West African navies is a factor that definitely influences the pirates' strategies," added Wade.

"However, it alone does not explain the increasing distances of the attacks, which also adapt to the behaviour of commercial ships trying to avoid high-risk areas."

The vast majority of sailors kidnapped by pirates last year -- 99 percent -- were working there when they were captured, according to a report by research institute Stable Seas and the United Nations Office on Drugs and Crime.

The French navy says attacks are increasingly following a similar pattern, with pirates trying to board ships and kidnap as many sailors as possible before setting off again.

Yet the further pirates operate from the coast the more likely it is they will encounter foreign war vessels.

France is one of few non-African nations to have a virtually permanent naval presence in the area.

In November, pirates were killed and captured in an incident with a Danish frigate off the Nigerian coast, creating a legal conundrum over the captives' status.

- Bridging the gulf in trust -

Maritime security in the Gulf of Guinea is complex, with several structures operating there without forming a cohesive unit to combat piracy.

The battle against piracy has kicked up tensions between African countries jealously guarding their independence and international partners anxious about the area's security.

African and European countries have set up separate forces, while some initiatives such as the maritime information-sharing platform YARIS attempt to unite all parties.

But too many cooks can spoil the brew.

Tim Walker of the Institute for Security Studies said African nations feel "uneasy" about the "relegation or marginalisation of African maritime security institutions that many are fighting hard to implement and grow".

Wade said the European Union's Coordinated Maritime Presence, which keeps vessels present in the area, involves "operational, legal and even political risks".

Although he conceded that European cooperation is a "central pillar" of security in the Gulf of Guinea, Wade said the steps taken so far have mostly failed to establish enough cooperation between European and African navies.

For Dirk Siebels, a senior analyst at Danish security intelligence company Risk Intelligence, international action is "badly calibrated" because it concentrates excessively on piracy and overlooks other illegal activities.

International operations were modelled on fighting Somali pirates, but the Gulf of Guinea is "completely different", he added.

"Somalia was a failed state and a transit zone for ships. It's very different in the Gulf, where ships call at the ports," added the French navy, which is calling for closer cooperation with local armies.

Walker concluded that lots of work must be done to satisfy all parties and improve the effectiveness of anti-piracy operations.

"International action against piracy in the Gulf of Guinea now has to demonstrate to coastal states that it seriously takes their concerns into consideration," he said.