Title

Aerial monitoring of responses of dugongs to underwater explosions at Triangular Island, in the Shoalwater Bay Defence Training Area.

Objective

To determine short-term (minutes-hours-days) responses by dugongs to detonations conducted in the intertidal zone of Triangular Island during Department of Defence training exercises.

Relevance

This project is part of an ongoing research program being funded by Defence to assess the effects of underwater explosions conducted at intertidal sites on Triangular Island during occasional Clearance Diver training courses. It will yield valuable information on dugong behavioural responses to the noise of detonations, and can also detect any inadvertent dugong death (although such impacts are considered highly unlikely based on all current evidence). Mortality should be readily detectable since the carcass will quickly become buoyant and rise to the surface due to rapid stomach and intestinal bacterial gas production.

Feasibility

Experienced observers using high wing light aircraft can successfully monitor dugong numbers and movements across relatively large areas containing shallow water seagrass feeding grounds, such as those within Shoalwater Bay. Key factors influencing the success of this method are wind strength and direction, since these can increase wave action and water turbidity and hence lower dugong sighting frequency and counting accuracy. To optimise dugong monitoring success with respect to local weather conditions during Clearance Diver training, the precise timing, location and type of the training detonations will be closely coordinated with the series of before, during and post-detonation flights undertaken for this project.

Methodology

Defence plans to contract one of Australia’s most experienced dugong aerial observers (Dr Tony Preen) to design and conduct the aerial monitoring program, which will use a high wing Cessna 172 (or similar) operating from Rockhampton or Yeppoon. This plane will be used to systematically monitor dugong movements in the three key areas in the region of Triangular Island most used by dugongs, as determined from the recent dugong satellite tracking study of Shoalwater Bay area (Preen, 1999). Pre-survey planning, pre-flight briefings and continuous radio contact with Defence personnel conducting the exercises on Triangular Island will be undertaken to ensure optimal coordination of the before, during and post-detonation flights with respect to weather conditions, visibility and detonation times.

Approximate Cost

$50 000

Time Required

Aerial surveys are planned to be conducted for the last two exercises in 1999 (September–November; ~5 detonations monitored per exercise). Requirement for a possible third survey in 2000 will depend on the results obtained.