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CONTROLLING CROWN-OF-THORNS STARFISH POPULATIONS
38. Can crown-of-thorns starfish be controlled? Approximately 15 million starfish have been killed in control programs throughout the last 15 years in the Indo-Pacific region. By far the largest of these programs have been undertaken in the Ryukyu Islands, Japan, where almost 13 million starfish have been removed from the reefs in that region. Despite these intensive efforts (costing approximately $A 6 million) the control program in Japan is regarded to have been unsuccessful in either eradicating the starfish or preventing further coral mortality. In fact, most control programs that have been conducted in the Indo-Pacific region are considered in this light. Only those undertaken in small areas (ie. less than one hectare) and at regular intervals are regarded to have achieved their objectives. Even this approach has not always been successful. For example, efforts at Green Island (during the 1960's) were not able to preserve a small coral viewing area despite the removal of about 44,000 starfish over a two-year period. On the basis of these results scientists and managers are generally pessimistic about the use of control programs, particularly their implementation on a large scale. Recently, several control exercises have been conducted by the Great Barrier Reef Marine Park Authority on reefs off Townsville. These trials were undertaken to determine the cost effectiveness of controlling crown-of-thorns starfish (see 41) and the potential for using other methods of control. Currently, the most effective control method is to inject starfish with a concentrated solution of copper sulphate. Previous methods have involved injection with ammonia, ammonium hydroxide, compressed air, acetic acid and collection by hand. The use of underwater fences has recently proven to be successful as a means of excluding adult starfish. Unfortunately, due to the high costs of erecting and maintaining these structures they are probably only useful for protecting small areas of reef. Further trials are needed to assess their potential for controlling starfish over much larger areas. The implementation of biological controls (such as diseases or predators) may be successful but it should be borne in mind that less than a third of all biological control programs undertaken in the world have been successful. Many of them have caused far greater problems in the environment than the original problems they were meant to overcome. A case of the cure being worse than the disease! Research is being conducted (see 39) to isolate and identify the diseases associated with the crown-of-thorns starfish, as a first step towards determining whether biological control is feasible.
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