XN000022-1995-06-29 — Page 12

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An analysis of water temperature, salinity, dissolved oxygen, turbidity, rainfall, tide, current and wind data has enabled him to develop a good understanding of the seasonal meteorological and oceanographic patterns that influenced the presumed movements of sharks into Hong Kong waters. He has reviewed information on mariculture, dredge-and-fill, and pollution patterns in Hong Kong waters and had related those activities to the attack problem.

He said: "From a predictive perspective, water temperature may prove to be the most important factor. Recent attacks occurred between May 31 and June 13 when rising water temperatures reached 25-26°C. Historical attacks recorded in late August to late September between 1945-1984 had also occurred in water temperatures of 25°C or higher.

"Salinity may also be important since the lower salinity waters of urban and regional beaches located west of Sai Kung have not yielded any attacks since 1955. The lower salinities of these waters, in combination with lower dissolved oxygen levels, higher turbidity, and increases in dredge-and-fill induced habitat loss and rising pollution levels appear to discourage sharks, and their natural fish prey, from frequenting these regions."

Furthermore, he pointed out, the summer monsoon which generally occurs in the mid-June to mid-August period, results in a change in wind and prevailing current directions from the east northeast to the southwest.

During this one to two-month period, waters from the western section of Hong Kong are partially pushed into the eastern sector, reducing salinities and dissolved oxygen levels and increasing turbidity. Presumably some water-borne pollutants are carried as well.

Shark attacks have not been recorded from this period (June 14 - August 25) in Hong Kong but late season (August 26 - September 23) attacks have occurred in the post-monsoon season when winds and prevailing currents return from east northeast, the last occurring in 1984.

Noting that the waters in Sai Kung have been the site of the last six attacks, Mr Burgess explained that this was because the district offered relatively clean marine

waters.

"Sharks apparently arrive in the area, or become more active, as water temperature rise in late May. They may become attracted to a steady stream of olfactory stimuli produced by aquaculture facilities located adjacent to the Clear Water Bay beaches, at Shelter Island near Sheung Sze Wan, and just north of Silverstrand Beach and Little Palm Bay.