POTENTIAL PROBLEMS

At any time, if the observer or driver feels conditions are unsuitable for towing they should assess the situation giving consideration to their safety. Listed below are some of the common problems that make towing conditions difficult.

• Rough seas: Generally on the Great Barrier Reef, the reef front receives the roughest seas on the southeast edge. Rough sea conditions can make it difficult and dangerous to manta tow, so drivers should know their limits. As a guideline, if the waves are greater than 2 metres, or breaking erratically then it is unsafe to manta tow. Note. This is only a guide and each person should use their discretion. If at any point one team decides to stop towing, then they must notify the other team by radio, and decide upon a point to continue towing where conditions are more suitable. If a break in the tow path is made, it should be clearly marked on the aerial.

• Currents: When there is a strong current flowing along the reef edge, towing speed and/or direction should be modified. If the current is going in the same direction as the boat, the driver should slow down to compensate for the speed of the water flow. If the current is against the boat, the driver should increase the speed of towing. However, if the observer finds towing difficult, the tow should end there and continue further around the reef perimeter where the current is less.

• Low tide: At low tide, the water may recede from the reef periodically exposing the crest. In this situation, the driver should keep a safe distance from the reef crest, to prevent the boat or the observer being caught in the surge. On a reef front where the wind is blowing the boat onto the reef, the driver should head the boat into the wind, especially when towing on a low tide to avoid being pushed onto the reef crest.

• Low visibility: Generally if the visibility is less than 6 metres, (ie. the nearest float on the tow rope is not visible) then surveys should not be conducted. However, if there is only a patch of low visibility water, then the observer should continue to record data if possible, and record the visibility change on the data sheet (see visibility section in data recording). The observer should beware of diving down in poor visibility.

• Channels: Occasionally the reef perimeter is broken by a channel that may be quite deep and/or have a strong current running through it. If the channel is deep (>9 m) and wider than about 25 metres, then the tow should end at one side of the channel and begin again at the other side. This break in the tow path should be marked on the aerial photograph.

• Sandy back areas: Some back reefs are typically shallow and lack a solid edge, making it difficult to determine the correct tow path. In these areas the driver must decide upon a straight tow path across the back reef to include as much hard substrate as possible. It is important to keep the orientation of the reef in mind when selecting the tow path and to mark any recognisable points on the aerial photograph.

AIMS home page

web@aims.gov.au
Last updated - 9 February 98

Copyright ©1996-1998 Australian Institute of Marine Science

URL http://www.aims.gov.au