Al Hallaniyat Islands Research Papers (original) (raw)

Mendonca VM, Al Kiyumi AA, Al Saady SM, Al Rasbiy A, Erzini K, Bait Said AS, Al Hamriy S, Grobler H. 2005. Sea turtle populations on Al Hallaniyat Islands. Proc 21st Int Symp Sea Turtle Biol Conserv. Philadelphia, USA, 2001. NOAA Tech... more

ABSTRACT
The Al Hallaniyat Islands in the Arabian Sea are under the influence of a seasonal monsoon from June to August-September, which enhances high algal and seagrass productivity, providing good feeding grounds for marine turtles. This archipelago consists of four islands: Al Hasikiyat, As Sawda, Al Hallaniyat and Al Qibliyat.
The only previous available information on this turtle population was recorded in the 1980s, when green turtles Chelonia mydas and loggerhead turtles Caretta caretta were observed to nest on the islands (Salm, 1991).
In this study, we carried out field observations in November 1999, February and October 2000, and identified turtle species, nesting beaches and seasons, and natural predators of turtle eggs and hatchlings.
The islands were extensively visited in February and October 2000. On most beaches on the islands, turtle tracks and nests, skulls and carcasses were identified. The total amount of turtle nests on each visited beach was registered, and classified in one of the following categories: < 1 week old, 2-4 weeks old, 1-2 months old, and > 2 month old. This helped to determine when the nesting season occurred. Local fishermen and villagers were also interviewed about nesting turtle species and nesting seasons. Finally, predators of turtle eggs and hatchlings on beaches, and human disturbance, were identified
Two turtle species were identified nesting on the islands: the green turtle Chelonia mydas and the loggerhead turtle Caretta caretta, nesting respectively in November - February and in May – September. However, it is likely that hawksbill turtles Eretmovhelys imbricata are also nesting on these islands, especially on those beaches of gravel or sand with coral rubble, as they do on Al Dimaniyat Islands, further north in the Gulf of Oman (Ross and Barwani, 1981; Salm, 1991; Mendonça, 2001).
Strong winds do not allow fresh turtle tracks or nests to last more than just hours or days, respectively, making very difficult any attempts to know the size of this turtle population, especially during the seasonal monsoon.
Al Hasikiyat Island: There were no turtle beaches on Al Hasikiyat Island. This island only has one beach, and too small to be a turtle nesting ground. However, it holds two large colonies of birds: masked boobies Sula dactylatra (at least 3,000 breeding pairs) and socotra cormorants Phalacrocorax nigrogularis (at least 5,000 breeding pairs). These seabirds and sooty gulls Larus hemprichii are the most important predators of turtle hatchlings on the Al Hallaniyat Islands.
As Sawda Island: On this archipelago, beaches on As Sawda Island were the ones where turtle nesting activity was more evident. On this island, rats Ratus ratus were identified as the most important turtle egg predator, as their footprints were found near empty turtle egg shells on some sites on the island.
Al Hallaniyat Island: The Al Hallaniyat Island is the only inhabited island of the archipelago, with 300 people. This island was the second (after As Sawda Island) with more turtle activity, especially on beaches of the southern side of the island. Remains of cooked green turtles were found on remote beaches on the island, and in the village damp yard. On this island, ghost crabs Ocypode spp. were on some beaches up to 6 ind.m-2. Ghost crabs are known to be predators of turtle eggs and hatchlings (Stancyk, 1995). On the other islands, ghost crab abundance was < 0.5 ind.m-2. Feral cats and seabirds were the main predators of turtle hatchlings on this isalnd.
Al Qibliyat Island
On Al Qibliyat: here were only gravel beaches, and 95% of the total nesting activity is on a single beach. The main predator of turtle eggs is the ghost crab Ocypode spp., and the main predators of hatchlings are seabirds, especially masked boobies (at least 5,000 breeding pairs).
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Note after publication: the turtles nesting on Al Qibliyat Islands are Hawksbills (Eretmochelys imbricata)