The octopus hunters of Zanzibar

Image copyrightTOMMY TRENCHARD

The powdery white beaches of Zanzibar's east coast are best known as a holiday destination.

But each day, as the tide begins to ebb and the beachgoers return to their hotels, a small army of men and women armed with sticks and spears wade out across the coastal flats in search of one of the Tanzanian island's finest delicacies - octopus.

Image copyrightTOMMY TRENCHARD

During a single low tide a skilled octopus hunter can spear more than 10 of the slimy invertebrates, which thrive amid the maze of rocks, corals and sea grass that lie beyond the beaches.

The catch is highly prized by the island's tourist hotels and provides an important source of protein for coastal communities.

Image copyrightTOMMY TRENCHARD

Protected by an offshore reef, the tidal flats off the island's east coast provide livelihoods and sustenance for local residents, in the form of fish, crabs, shellfish, seaweed and octopus.

Image copyrightAURELIE MARRIER D'UNIENVILLE

Tanzania is the largest producer of octopus in the western Indian Ocean.

Image copyrightTOMMY TRENCHARD

Abdullah Ali, 35, prepares to launch his traditional wooden boat on an octopus hunting expedition from Dongwe village.

Traditionally a female-dominated activity, more men are now turning to octopus for a source of income.

Image copyrightAURELIE MARRIER D'UNIENVILLE

"The octopus has helped me to drive my life forward," said Ali, who makes about £1.90 ($2.30) per kg (2lb 3oz) for his octopuses.

Image copyrightTOMMY TRENCHARD

According to data from the UN's Food and Agriculture Organisation, catches in Tanzania have increased from 482 tonnes in 1990 to more than 1,250 in 2012.

Image copyrightTOMMY TRENCHARD

The mix of jagged rocks and corals near the reef offer many places for the octopuses to hide at low tide, becoming almost invisible to the untrained eye.

Thousands of sea urchins provide a further challenge.

Image copyrightTOMMY TRENCHARD

Mariam, an octopus hunter from Bwejuu village, plunges into the water to cool off after a morning's work.

Image copyrightTOMMY TRENCHARD

Mama Juma, a seasoned octopus hunter, scans the crystal clear water near Paje beach for likely octopus hideouts.

Image copyrightAURELIE MARRIER D'UNIENVILLE

A lone woman searches for octopus in the evening beyond a seaweed farm at Bwejuu.

Local communities derive much of their livelihood from the intertidal flats.

Image copyrightTOMMY TRENCHARD

Grilled octopus is a staple at the nightly seafood market in Stone Town.

Most of mainland Tanzania's octopus catch is exported to Europe, but on the island of Zanzibar tourism has provided a booming market.

All photographs by Tommy Trenchard and Aurelie Marrier d'Unienville