For centuries, the oyster beds located off the northern shores of Bahrain were described in superlative terms for the quality of their pearls, the density of their oysters, and the high ratio of pearl discoveries made during the pearl collecting season. In his Natural History, Pliny the Elder (23/24–79 AD) named the island (then Tylos) as “extremely famous for its numerous pearls”.
The reputation of Bahrain’s oyster beds as the richest in the Arabian Gulf meant that in the season, pearling dhows from Qatar, Kuwait and the South Persian coast sailed to join pearling fleets from Muharraq and the main island of Bahrain in the quest for the prized natural treasures. They were able to do so because the waters of the Arabian Gulf were considered the common property of all its coastal dwellers.
The Bahraini oyster beds proposed for World Heritage nomination are Hayr Shtayyah, Hayr Bu ‘Amamah and Hayr Bu-I-Thamah. Occupying nearly 35 thousand hectares and populated by well over a billion oysters, the beds are also home to diverse marine species such as corals, anemones, sea stars and fish. They have been selected to represent the distinctive qualities of the Bahraini oyster beds and their popularity as a pearl diving location among the Arabian Gulf’s pearling fleets.
— HaBū-l-Thāmah
Of the three Bahraini oyster beds proposed for nomination, Hayr Bu-I-Thamah has the strongest reputation among former divers and dhow captains as a source of real treasures. With an average depth of 20 metres, it is the deepest of the three beds, and may also have the highest density of oysters in the Arabian Gulf. Its reputation for producing large and beautiful pearls (Arabic: danat; sing. danah) may have given divers the courage to dive to the bottom of this deepest of beds. It may also have motivated captains to head to the bed, 65km from the northern shores of Muharraq Island, as soon as the divers were up to the water depth.
— Hayr Bū ‘Amāmah Oyster bed
Known during the pearling era for its extremely high density of pearl finds to oysters, Hayr Bu ‘Amamah was probably the most popular oyster bed during the main pearling season and was frequented by pearling dhows from ports around the Arabian Gulf. With its extremely high density of pearl finds to oysters, Hayr Bu ‘Amamah promised the divers good finds even with an average underwater density of oysters (4-20 per square metre). Located 63km northwest of Muharraq Island, it has an area of around 4.8 thousand hectare and is the most western of the important oyster beds. Its water depth is a fairly constant 15 metres, with visibility averaging around 10 metres. Previous surveys have estimated the number of oysters on the bed at 482 million, and the surveyors have found the oysters in a healthy condition. The sea anemones, sea urchins, sea stars and a colourful variety of fish, molluscs, corals and sponges found at Hayr Bu ‘Amamah make it a fascinating place of discovery for scuba divers.
Included as a marine protected area since 2007, Hayr Bu-I-Thamah is in excellent environmental condition and enjoys a high degree of control over fishing and trawling. Although the water quality is also excellent, with the oyster bed demonstrating a high species diversity, especially in its range of living corals, visibility is limited to about 7 metres. This could result from the additional water depth and resulting stronger current, or from the movement of the inhabitants of the coral reef.
— Hayr Shtayyah Oyster beds
Located 24 nautical miles (44km) off the northern shores of Muharraq Island, and with an area greater than 24 thousand hectare, Hayr Shtayyah, was a popular anchorage at the opening of the pearling season. Importantly, it is one of the shallowest oyster beds, with high visibility, making it a favoured location at the start of the season when pearl divers had to rebuild their form after eight months onshore. Second, the water temperature of Hayr Shtayyah is some three degrees warmer than the temperature of deeper oyster beds, a significant difference, particularly during the colder first and last weeks of the season, for divers who had to spend up to two hours in the water without a break. Finally, the cluster formation of Hayr Shtayyah’s oysters made them easier and faster to collect. Oyster clusters were also believed to be a good source of pearls. A 2008 survey of Hayr Shtayyah found that the oyster bed remains in good condition, with a pearl oyster density varying from 4-30 oysters per square metre, and a rich habitation by fish, echinoderms, molluscs,corals and sponges.