PROCEDURE

On arrival at a reef, the following procedure should be adopted.

• The two teams discuss the location of the starting point, manta tow path and weather conditions before commencing the survey. The cruise leader must ensure that everyone is aware of tides, currents, daylight hours remaining, and present weather conditions.

  Note. If the weather is expected to change for the worse, the teams should agree on a strategy before leaving the ship. Radio contact with the ship and between boats should always be maintained. This is particularly important on large reefs where the two boats may be out of visual contact.

• Begin the survey at the set starting point (usually at the northern end of the reef) unless conditions are unsuitable. Note. Factors such as wind, direction of current, and angle of sun may alter the starting point. The driver should avoid towing into the sun continuously, where possible. Mark the starting point as '0' on the aerial photograph. (The two boats start together but proceed in opposite directions around the perimeter of the reef, meeting up at the other end.)

• Clip the tow rope to the transom harness so that it can move freely, and attach the other end to the manta board with the quick release clip. The observer should then record the ambient variables, such as weather conditions on the top of the data sheet (Appendix I), don snorkelling gear, and enter the water with the manta board.

• The observer signals the driver to commence the manta tow when he/she is ready. The observer and driver use hand signals to communicate information about the tow path and the towing speed (see English et al. 1994). The driver tows the observer holding the manta board, behind the boat at a constant speed of about 4 km/hr (the actual speed may vary, depending on wind and current). Note. Observations are generally made from the surface, however when closer inspection is required, the observer can manoeuvre the manta board below the surface. To dive down, tilt the leading edge of the board down, and tilt upwards to ascend.

  The tow path should be parallel to the reef crest, and close enough for the observer to see as much of the reef slope as possible. The search area will vary, depending on tow path, speed of the boat, visibility, reef gradient, distance from substrate, distribution and density of organisms being counted (Moran & De'ath 1992). This variability of the reef slope and weather conditions make it difficult to define a search area however, observers should consciously try to restrict their search width to about 10 metres (see English et al. 1994).

• The driver times the manta tow and stops after two minutes by idling the motor. The tow rope will become slack allowing the observer to record the data for that tow (ie. COTS number and size, percentage cover of live and dead coral, sand/rubble and presence of feeding scars). The driver should keep a record of the number of tows and where possible, mark the tow number and position on the aerial photograph (Figure 3). When the observer signals that the data recording is complete, the driver recommences towing, stopping again after two minutes.

• The observer and driver change roles after an agreed time, (usually after fifteen tows) to avoid fatigue. During the changeover time, it is important to discuss observations about the reef and sea conditions.

• This procedure is repeated until the entire perimeter of the reef is surveyed. Thus, a completed survey consists of a series of consecutive two minute tows.

Figure 3. Reef aerial maps showing numbered tow paths for each boat.

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