Swooping over a cloud of seagulls off Senegal's sparkling shores, a French military airplane veers past a fishing trawler, the naval officers onboard keeping a watchful eye out for illegal activity.

The West African country's waters are some of the richest in the world, teeming with tuna, sardines, shrimp, lobster and octopus -- and fishing is critical to the economy.

But stocks are dwindling due to global warming and overexploitation.

While local artisanal fishermen account for 80 percent of the country's total catch, they have for years raised the alarm about competition and harmful practices by European and Chinese companies.

To help tackle overfishing, the Falcon 50M -- a French Navy aircraft -- is one of several rotated year-round on loan from the Lann-Bihoue base in France.

During the airplane's patrols, five French soldiers and a Senegalese inspector scan the Atlantic for signs of bad behaviour.

This can range from fishing in restricted areas, fishing without a licence, or using destructive nets which sweep up species like dolphins and sea turtles or damage the sea floor.

"On the right, we have an echo at eight nautical miles," a radar operator announced during a recent visit by AFP.

White and red arrows blinked on his screen, representing different vessels near the border with Mauritania, as the radio crackled with coded messages.

Whenever suspicion is aroused, the plane descends and soldiers snap photos.

"We have 600,000 people working directly or indirectly in the fishing industry, and millions of people depend on it, so it's important to monitor how the resource is being exploited," said Captain Ibrahima Diaw, head of Senegal's fisheries protection and surveillance department.

In the event of a violation, a report is drawn up. In exceptional cases, the Senegalese Navy can send a ship to seize the offender.

Last year, the Falcons inspected nearly 600 vessels, according to the French Navy.

Reports were drawn up in 35 cases, Diaw said, describing that number as "huge".

Fines can reach up to 30 million CFA francs ($50,000).

The military deal illustrates the ongoing close ties between Paris and its former colony.

According to the NGO Environmental Justice Foundation, Senegal loses more than $270 million in revenue each year to illegal fishing.

Fishing makes up 3.2 percent of the country's gross domestic product and 10.2 percent of exports, according to a 2022 US Department of Agriculture report.