Cold weather has delayed the release of green sea turtles hatched artificially last month. Twenty-three turtles were hatched by researchers at the Agriculture, Fisheries and Conservation Department from 107 eggs laid by a green turtle in September at Tai Long Wan, Shek O. All of the turtles, except five which have unusual shell patterns and are being cared for by the department, are being raised temporarily at the Ocean Park aquarium. They are now five to six centimetres long and will be released in eight months when the water temperature rises and they grow strong enough to resist predators. Those with the unusual shell patterns will be kept for further study. Separate clutches of 268 eggs laid at Sham Wan Beach on Lamma Island in June and August failed to hatch. These eggs were left in their nests at the beach, which was designated a restricted area from June to October. Simon Chan Kin-fung, acting senior wetland and fauna conservation officer, said several factors could influence whether turtle eggs hatched, including variations in temperature, humidity and sand composition. 'The most likely factor leading to the infertility of the whole clutch of eggs is that they are not at all fertilised. This is commonly found at other natural hatching grounds elsewhere in the world,' he said. The green turtle is a critically endangered species and is internationally protected under the Convention of International Trade in Endangered Species of Fauna and Flora. Female turtles usually lay hundreds of eggs at least twice a year, but only about one out of 1,000 survives to adulthood. In Hong Kong, green turtles usually appear during summer on southern and eastern coasts.