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Part Two: Scuba Search Technique
TECHNIQUE Introduction SCUBA searches were used in conjunction with manta tow surveys to provide quantitative measures of abundance of COTS (Endean 1974, Kenchington & Morton 1976, Roads & Ormond 1971). More recently, SCUBA searches have been employed to investigate possible biases in manta tow surveys (Fernandes, 1990, Fernandes et al. 1990). SCUBA searches are used to examine the reef in greater detail than is possible with the manta tow technique. They provide important additional information for COTS surveys, enabling: 1. The detection of low densities of COTS, because they are usually cryptic and more difficult to detect using manta tow. 2. A method for the detection of juvenile COTS which, because of their small size and cryptic behaviour, are not easily seen by a manta tow observer. 3. The diver to detect other factors that may be causing coral mortality such as Drupella, bleaching or disease (eg., white band and black band disease). Historically there have been few reports of high density populations of juvenile COTS on the GBR and these have involved only small areas of reef and very few COTS (Pearson and Endean, 1969; Fisk et al. 1988; Doherty and Davidson, 1988). The detection of juvenile starfish provides a basis for understanding recruitment events and forecasting population increases. The aim of SCUBA searches in the Long-term Monitoring Program is to detect COTS and/or coral mortality that may not be visible by manta tow. Two methods of SCUBA searching are used, fixed and timed transects. Sampling procedure The following section outlines the procedure for undertaking SCUBA search surveys for coral mortality on the long-term monitoring sites on the GBR. For a detailed description of the other surveys conducted on these transects see Halford and Thompson (1994) and Christie et al. (1996). 1. On completion of surveys of the five, 50 metre by 5 metre transects, the fish observer returns along the transects (which are marked with a tape along the centre line) counting Pomacentridae fish in a 1 metre wide strip up the reef slope from the tape. 2. The diver who lays the tape follows the fish observer winding up the tapes. At the same time, this person conducts a fixed transect search to look for coral mortality, the presence of COTS and Drupella. Sampling procedure 1. Each reef is initially manta towed to select sites by the presence of feeding scars and/or COTS. These sites are noted during the manta tow survey and marked with a buoy. Upon relocating the site, the position is recorded using a GPS. Divers should search three to six sites on a reef if possible. 2. Ideally three divers each swim parallel to the reef slope along three separate depth contours (4 m, 8 m and 12 m). However, this will depend greatly on the topography of the reef slope. Where the slope is less than 12 m, divers should swim parallel to each other, (4 metres apart) covering the maximum practicable depth range between the crest and the base of the reef slope. 3. Each diver swims for twenty minutes and scans approximately 1 metre either side of the swim path looking for evidence of coral mortality. Areas of recently dead coral should be examined to determine the cause of mortality, and observations are recorded on the data sheet (Appendix III). Data recording The data sheet is a table consisting of the following columns: GPS/Transect The number of the transect surveyed for a fixed transect, or the position recorded with the GPS for a timed swim search. COTS COTS numbers recorded as J, A or B, according to size criteria listed in Table 4. COTS scars The number of individual feeding scars attributable to COTS Drupella Individual Drupella species are counted. Drupella scars All feeding scars directly attributable to Drupella are recorded in this column. Searching near these scars may reveal an aggregation of Drupella. One feeding scar is defined as a contiguous area of recently dead coral on a colony. Scars unknown Any scarring where there is no obvious cause apparent. Bleaching The percentage of coral bleached along the transect is recorded as a category from 0 to 5 (same categories as used for the manta tow technique, Table 5). Comments Notes about coral mortality or health (such as black band and white band disease) recorded on the corresponding numbered line below the data table.
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