TRAINING NEW PERSONNEL

The AIMS manta tow technique while being relatively precise and cost effective is still subject to a variety of biases. Logistic constraints and the nature of the environment prevent total resolution of bias (Fernandes et al. 1989). However, standardisation and the use of trained observers can reduce methodological biases and enhance the precision of estimates (Miller 1994). The use of trained observers is vital to the technique as the observers' perceptions form the basis of any data recorded. Observers should concur in all aspects of the survey. To achieve the levels of competency necessary for manta tow surveys, it is important that a coordinated training program is conducted.

Procedure

Introduction to manta towing

The first part of the training exercise is to introduce new personnel to the manta tow technique. This is done by familiarising them with the historical development of the technique and how it is currently applied (Moran et al. 1989, Moran & De'ath 1992, English et al. 1994). A discussion with experienced observers to debate the advantages and disadvantages of manta tow as an ecological sampling method also helps to understand the technique. The second part involves showing slides and video footage of coral and other benthic cover to familiarise the new personnel with the different types of cover present on a coral reef. This includes discussion of common problems such as the definition of dead coral and how to estimate the appropriate cover categories (ie. live coral, dead coral and sand and rubble).

Field training

Initially inexperienced observers need to familiarise themselves with the practical aspects of being towed before recording data. Once they are happy with this, they are towed in tandem with an experienced observer on a 'double board' (Miller 1994) to learn how to record data. This enables the inexperienced observers to become familiar with estimating coral cover by comparing their estimates with the experienced observer over the same area. This technique enables paired observers to recognise and compensate for any variations between their COTS counts and benthic cover estimates. Inexperienced observers should tow with different experienced observers to avoid personal biases.

QUALITY CONTROL

The precision of estimates is expected to vary between observers because estimates are influenced by a variety of factors (Moran & De'ath 1992). To obtain the most precise estimates and to detect 'drift' (defined as a consistent movement or difference in the direction and magnitude of bias between observers over time) between experienced observers an ongoing system of quality control is employed.

This is done by 'double towing' selected reefs to give a measure of the variability between observers over a period of tows. Where problems in estimation occur (Miller & Muller, 1997) then observers are retrained using the two person manta board. This system is perceived to have a number of advantages:

• It can detect problems with individual observers and groups of observers as they arise.

• It provides a means where observers can compare their estimates in the field and form a consensus on cover estimation.

• It provides an ongoing estimate of the precision of surveys as they occur in the field.

• Because training is ongoing, problems in estimation can be identified and dealt with as they arise thus lessening the need for annual training of all personnel in the field at one time.

To 'double tow' a reef, two boats are used, but instead of towing in opposite directions around the reef, the two boats go in the same direction. One boat follows about 100 m behind the other in a clockwise direction around the reef. Thus, each boat will drive around the entire perimeter of the reef resulting in two complete data sets. This procedure takes twice as long to survey a reef, so only reefs which are less than 30 tows are selected for double towing. A minimum of three reefs should be double towed each survey trip to allow each of the 4 observers to be compared.

• Two pairs of personnel (A, B and C, D) begin to manta tow the reef. The second pair follow at about 100 metres behind the first boat.

• After 15 tows, or after half of the total number of tows expected for the reef, the first pair (A and B) stop, and wait for the other pair (C and D).

• The observers compare their cover estimates.

• Observers and drivers from the same boat then swap roles. This procedure is continued until the whole reef is towed.

• At the next reef, comparisons are made between different observers (boat pairs; A, D and B, C). The observers and drivers change combinations at each reef. In this way, each of the 4 people are compared to each other during a survey trip.