Ahmed Ali Mohamed snorkels over sea grass and coral, keeping an eye out for different fish species darting through the waters below him.

But his job is not to catch the fish -- as his family has done for generations -- instead he only counts them.

Mohamed is one of the first former fishermen to be retrained as a ranger monitoring the health of the reef off Pate Island in southeastern Kenya, where fortunes are dwindling as fast as the fish in the sea.

Pate's fishermen have plied the inshore waters for generations but must now adapt to survive as -- like coastal people around the world -- they learn the hard way that the ocean is not an endless resource.

"The community's population has grown with time and we all depend on the ocean alone for a living," said Mohamed, 45, a former lobster fisherman.

"Before people would go into the waters and come back with a big catch of fish... but now they don't even come back with enough to feed their own families."

The stakes are high for the island, the largest in the idyllic Lamu archipelago.

Fishing became the main source of income after tourism collapsed following a spate of kidnappings by pirates in 2011 and an increase of attacks by Shabaab militants on the mainland.

Community leaders fear the effects of worsening poverty as the fish run out in this mainly Muslim region which neighbours Somalia and has suffered generations of marginalisation by successive governments.

"When it comes to a point where people have nothing to do, no income, (and) increase in poverty, people will have no option but to end up joining bad groups like Al-Shabaab," said Atwas Swabir, the chairman of Pate's marine reserve.

- Fishermen target reefs -

Poverty is already entrenched. On the mangrove-fringed island, electricity only reached the torpid fishing village of Faza two months ago. Dozens of children loiter on the shore while donkeys nibble at flotsam in the water and scrawny, diseased cats yowl for scraps when the fishermen come in.

Swabir says many of these children will end up as fishermen "whether they like it or not" so finding new ways to make fishing sustainable without destroying the environment for future generations is essential.

"Fishing is not just an income generating activity, it is a lifestyle," said local fisheries director Kamalu Sharif. "You cannot remove a fisherman and take him to the farm."

Close to where Mohamed takes careful notes on an underwater writing slate, traditional wooden dhows work in tandem to drag a large tight-mesh net over the reef scooping up everything in its wake, including young fish, and breaking off bits of sensitive coral.

The reefs teem with fish who are lured there for breeding, making them an easy and vulnerable target for fishermen.

"That is where breeding happens, that is where (fish) lay their eggs. The fishermen are directly targeting those reefs," said Juliet King, an advisor to Kenya's Northern Rangelands Trust (NRT), a conservation organisation.

The reef ranger programme, funded by the US-based Nature Conservancy, is aimed at helping fishermen manage their resources better, using a method akin to crop rotation to encourage sequential fishing of the reef giving different areas a chance to recover.

However, the long-term plan is for fishermen to move away from the sensitive reef entirely. Currently, they only use a fraction of the more than 200 nautical miles of waters available to them.

"We are trying to encourage (the fishermen) to extend their fishing range to slightly deeper waters and in less exploited areas and that way we will be tackling this big problem of overfishing," said George Maina, Marine Project Coordinator for the Nature Conservancy.

Lending the project more urgency is the nearby construction of a major new port, a boon for development that spells doom for the livelihoods of around 4,000 fishermen if they remain inshore, say local officials.

Further out, they can catch larger, more valuable fish, but that requires ice for storage and a market at which to sell them.

- New methods, bigger earnings -

Testing a new initiative, dhows set off from Pate at night with ice boxes on board. In the deeper waters beyond the reef, they will fish with a hook and line instead of nets.

The next day, the prized catch of snapper, tuna and emperor fish is whisked to a nearby hotel -- which has rented a freezer to the fishermen -- before being sent on to upmarket restaurants and lodges across Kenya.

Taking part in this pilot programme, Mohamed Mwanaheri, 40, says he has more than doubled his earnings.

"People need to be informed so that the community can know there is a ready market (and) change their outdated fishing methods," he said.

Fuzz Dyer, an advisor to NRT and the owner of the hotel where the fish is frozen, reckoned Pate's fishermen could land 400 kilogrammes (880 pounds) of high-quality fish a day if they are helped to change their methods and access the market.

The alternative, Dyer warned, is disaster with overfishing leaving the reef barren.

"People are just raping the bottom of the ocean," he said.