ENG-1975 — Page 259

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NATURAL HISTORY

Atlas and Moon moths. The Atlas species has an average wing span of nine inches and the Moon seven inches. Two of the local plant bugs are noted for their colour and shape. They are the rare and beautifully spotted Tea Bug which has only been recorded on hill-tops, and the Lantern Fly which has delicately coloured wings and a remarkably long forehead. Dragon and damsel flies are commonly found, as are wasps and metallic-coloured beetles. Of particular interest is the Large Spotted Batocera Long-horn Beetle, which feeds on mountain tallow trees.

The African Giant Snail is the largest of the land molluscs, with a record length of six inches. This species was introduced in 1938 and has become a crop and garden pest. The large black slug, Veronicella, is sufficiently different from all other slugs to be placed in a separate family.

Aquatic Life

Marine life forms in Hong Kong are diverse and mainly tropical in character, comprising a relatively large number of commercially important species of fish, crustacea and molluscs. The discharge of the largest fresh water system in South China to the west, and the prevailing influence of offshore water masses in the north-east, have created a situation where the westerly sector of Hong Kong has a predominantly brackish water fauna, while the eastern sector has a genuine marine fauna.

Pomfrets (Parastromateus niger and Stromateoides spp), croakers (Argyrosomus spp), hairtails (Trichiurus spp), and ponyfish (Leiognathus spp) occur commonly, especially in autumn. A variety of isospondylous fish, such as sardines (Sardinella spp), shads (Clupanodon spp) and long-jaw herrings (Thrissa spp) may also occur in large schools seasonally. However, the yellowtail (Seriola quinquilineata), mackerels (Scom- beromorous spp) and yellow croaker (Pseudosciaena crocea), which were abundant, have now diminished in stock size. The natural bays and inlets of Hong Kong also serve as nursery grounds for a number of species, notably the Sparidae, Lutjanidae, Carangidae, Engraulidae and many others.

From time to time dolphins are sighted in Hong Kong waters and identifications have included the Common or Saddle-back Dolphin (Delphinus delphis), the Black Finless Porpoise (Neophocaena phocaenoides) and the Chinese White Dolphin (Sotalia chinensis).

Since its introduction more than 100 years ago, the Japanese oyster (Crassostrea gigas) has been successfully established in Deep Bay, where it is now commercially cultivated.

The freshwater fauna of Hong Kong is relatively poor in variety compared with that of South China. This probably results from the absence of a perpetual system of rivers and lakes. Although there are large quantities of water stored in man-made reservoirs, only a few varieties of fish life have been introduced-primarily for water quality control purposes. The indigenous fauna comprises only limited species of cyprinid, loach and goby. The African Tilapia has established itself in local waters but its initial introduction cannot be traced. Hong Kong now has some 3,500 acres of commercial fish ponds, where the Grey Mullet and seven species of Chinese carp are being produced at a rate of 1.2 tons per acre a year.