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NATURAL HISTORY
species of snails that are common vegetable pests. Farmers are troubled by several slugs; one of these - Veronicella - is a large black slug sufficiently different from all other slugs to be placed in a separate family.
Aquatic Life
Geographically, the seas around Hong Kong are a transient region, covering the northern limit of the tropical Indo-Pacific, and the southern limit of the temperate Chinese and Japanese marine life. Because of the presence of large coral reefs, there are more than 2,000 fish species; these are especially diverse in form, variety and colour. Many are exploited commercially. Of note is the large number of colourful coral reef fishes recently introduced to, and well established in, the live marine fish trade.
The waters of Hong Kong can be broadly divided into a western sector, influenced by the Pearl River and predominantly brackish, and an eastern sector, subject to the influence of the open sea. They provide natural propagation and nursery grounds for many commercial species of fish, crustacea and molluscs, and provide seasonal feed- ing for large transient predators, such as the Little Tuna, Dolphinfish, Sailfish and sharks. The Whale Shark, one of the largest fish in the world, has been observed in Mirs Bay.
Under the circumstances, the high productivity of local waters results in the seasonal occurrence of many commercial marine fishes either in juvenile to late juvenile forms, or of species low in the food chain, such as the clupeioids. These, and the transient predators, form very rich fish resources for commercial exploitation.
The presence of abundant fry and fingerling stocks of many percoid fishes has stimulated the development of lucrative floating cage culture fisheries. In 1977, produc- tion was estimated at 563 tonnes.
However, increasing land development activities through reclamation and dredging of the sea, with consequent dumping of spoil at sea, have already given clear indica- tions of adverse effects on the well-being and survival of marine life in these waters.
Dolphins continue to frequent Hong Kong waters seasonally. The green turtle has been reported to have returned to one of the islands, though in small numbers.
The culture of the Japanese oyster in Deep Bay continues. The abundance of the green mussel in Hong Kong waters suggests that this fast-growing bivalve mollusc also could be cultivated for commercial purposes.
The freshwater fauna of Hong Kong is poor by virtue of the artificial destruction of natural freshwater systems and geographic limitations. Freshwater fish culture follows traditional Chinese systems and has continued to expand, while improved management has led to higher unit yields.
Flora
For so small an area, Hong Kong has a large and diverse flora. The territory is situated near the northern limit of the distribution of tropical Asian flora. It is estimated that there are about 2,500 species of vascular plants, native and introduced. Except for the most recent discoveries, these are listed in the Check List of Hong Kong Plants (Agriculture and Fisheries Department, 1974). A new illustrated book, the Wild Flowers of Hong Kong, by B. M. Walden and S. Y. Hu, was published early in the year.