Sea turtles used to be very numerous in Hong Kong waters but their numbers have declines dramatically. Here for the sake of reminding us all what we once had (and could have again if we work hard and exercise self-discipline) – species of sea turtle recorded in Hong Kong waters:
1. The Green Sea Turtle (Chelonia mydas) – Endagered
the only sea turtle species known to breed in Hong Kong
Green Turtles are so far the only species known to breed locally. Adults attain a maximal shell length of about 120 cm and a weight of about 300 kg. The shell of the adults are broad and oval-shaped, dark brown to grey in colour. Their common name “Green Turtle” is actually derived from their fat which gives a dull greyish green appearance. The fat and cartilage of green turtles were once used in the making of soup – a delicacy on the western menu in bygone times. Juvenile green turtles feed on jelly fish, small fish and shrimps. The adults switch to a mostly vegetarian diet of algae as the major staple. Other sea turtles species prefer a meaty diet.
The regular nesting site is situated at the sandy beach of Sham Wan and the nesting season lasts from June to October. From 1998 until 2011, from 3-7 clutches of eggs have been delivered by female green turtles, each with about 100 eggs laid at intervals of 12 to 14 days in a nesting season. The summer of 2012 was the last time a female laid 5 clutches of a total of 550 eggs there. Unfortunately, there was no sign of hatchlings in the incubation period. A possible reason for this is that the eggs were unfertilised. The very same same turtle also nested in Hong Kong in 2003 and in 2008.
AFCD has restricted access to Sham Wan during nesting season and enforces strict control. Do not enter the area during nesting season!
2. Leatherback Sea Turtle (Dermochelys coriacea) – Critically Endangered
The largest turtle in the world, weighing over 1000 kg (1 ton). Their bodies covered by tough leathery skin rather than a shell. The shell is black with white spots and has seven prominent keels running down its length. The underside is white.
Feeds almost exclusively on jellyfish and has a throat-lining that prevents penetration of jellyfish stings. It can travel long distances in the open ocean and can dive very deep to forage. It is know to sometimes migrate to cold Arctic waters to feed and is the only known reptile that can remain active in water below 5°C. It occurs worldwide from tropical to sub-polar oceans, but nests on tropical beaches and smaller individuals are limited to areas warmer than 26°C. It is very rare in Hong Kong waters and was first reported from Cheung Chau Island where one turtle went onto the beach and later returned to the sea. It was also sightred: in Lei Yu Mun in 1964, and a dead individual was found at a beach in Sai Kung in 1977 and again in 1988 and a dead adult was also found in Tung Lung Island in 1994. It does not breed in Hong Kong.
3. Hawksbill Sea Turtle (Eretmochelys imbricata) – Critically Endangered
The shell is elliptical, with characteristic overlapping plates (scutes) on the back. Each back and fore flipper has two claws.
The shell is amber/ground coloured, with black or mottled brown colour. The head is narrow with a strongly hooked jaw. After hatching, small juveniles and migrating animals are found in open ocean waters. Larger juveniles and adults forage for food at the sea bed in habitats including coral reefs and sea grass and algal beds, mudflats and mangrove bays. The adults nest on sandy beaches, primarily under vegetation. Their diet includes gastropods (snails), cephalopods (squid and octopus), crabs, sponges and algae. Most hawbills turtles nest at night during the warm and rainy season, generally starting at the end of spring. The clutch size is around 140 eggs. There is only one record of a Hawksbill turtle in Hong Kong. A stranded dead individual was found on a beach near WWF Island House Centre in Tai Po in April 2004. But it is known from the provincial waters of Guangxi, Hainan, Guangdong, Fujian, Zhejiang, Jiangsu and Shandong. It may stray into Hong Kong waters occasionally. It is a circumglobal species occurring in tropical to subtropical waters, and found in the waters of 108 countries, with nesting occuring in 70 countries. Two hawksbill turtles which were nursed to health by AFCD and OPCF and were released back into southern waters of Hong Kong in August 2012 (read previous post here).
4. Olive Ridley Sea Turtle (Lepidochelys olivacea) – Vulnerable
The shell is heart-shaped, olive-green in color with a single keel down the middle of the back. The underside of the shell is pale orange-yellow and each flipper has one claw. Its omnivorous and feeds on fish, lobster, jellyfish, seagrass and algae. In China it nests on beaches and lays eggs between September and January. The cluthes are between 90 and 135 eggs and the eggs hatch within 2 months. The Olive Ridly is occasionally seen in the southern and eastern parts of Hong Kong waters and there are five records with certainty in Hong Kong: in 1973 at a beach on Stonecutters Island, in 1978 a live individual in the sea off Shau Kei Wan, one shell of this species was also found ashore on Lamma Island, in 1996 a recently dead adult was found at Shek O and in 2005 (June 1) a 32 kg female carcass was found on a rocky beach near Ocean Park. Its generally found around the tropics and its migratory route is in tropical and partly in subtropical waters (over 80 countries). It nests in tropical waters in nearly 60 countries worldwide.
5. Loggerhead Sea Turtle (Caretta caretta) – Endangered
The shell os 79-114 cm long and heart-shaped with a pale yellow underside. The hatchlings are grey to brown in colour.
The flippers are reddish brown and each front flipper has two claws. Males have a narrower shell and thicker and longer tail. It feeds mainly on crabs, mollusks (snails, shellfish), shrimp and jellyfish. One specimen was caught near Hong Kong, but the exact locality is not known. But it is not known from the waters of any other provinces along the coastline of China. The species has a circumglobal distribution, primarily temperate waters.