Once in the field, the boat captain navigates to previously selected sites using a handheld GPS unit. On-site, divers are deployed and maintain contact with each other throughout the entire census. One diver is responsible for collecting data on the fish communities utilizing the belt-transect visual census technique over an area of 100m2 (25m length X 4m width). The belt-transect diver obtains a random compass heading for the transect prior to entering the water and records the compass bearing (0-360o) on the data sheet. Visibility at each site must be sufficient to allow for identification of fish at a minimum of 2m away. Once reasonable visibility is ascertained, the diver attaches a tape measure to the substrate and allows it to roll out for 25m while they are collecting data.
Although the habitat should not be altered in any manner by lifting or moving structure, the observer should record fish seen in holes, under ledges and in the water column. To identify, enumerate, or locate new individuals, divers may move off the centerline of the transect as long as they stay within the 4m transect width and do not look back along area already covered. The diver is allowed to look forward toward the end of the transect for the distance remaining (i.e. if the diver is at meter 15, he can look 10 meters distant, but if he is at meter 23, he can only look 2 meters ahead).
On-site, no attempt to avoid structural features within a habitat such as a sand patch or an anchor should be made as these features affect fish communities and are "real" component of the habitats. The only two instances where the transect should deviate from the designated path is to stay above 110 ft (limitations imposed by diving) or while surveying mangrove habitats. In mangrove areas, the diver swims close to the prop roots and looks as far into the mangroves as possible; up to 2m and then out to the edge of the mangrove overhang such that the total area surveyed is still 100m2. In this case, some of the survey may necessarily fall on seagrass habitat. This is allowed as the mangrove habitat is defined as a transition zone habitat. The transect should take 15 minutes regardless of habitat type or number of animals present. This allows more mobile animals the opportunity to swim through the transect, and standardizes the samples collected to allow for comparisons.
Data are collected on the following:
1) Logistic information - diver name, dive buddy, date, time of survey, site code, transect bearing.
2) Taxa presence - as the tape roles out at a relatively constant speed, the diver records all fish species to the lowest taxonomic level possible that come within 2m of either side of the transect. To decrease the total time spent writing, four letter codes are used that consist of the first two letters of the genus name followed by the first two letters of the species name. In the rare case that two species have the same four-letter code, alternate four-letter codes are used to distinguish between the species. These alternate codes contain the first two letters of the genus, the first letter of the species and then the first letter in the species name that differs from the other code. If the fish can only be identified to the family or genus level then this is all that is recorded. If the fish cannot be identified to the family level then no entry is necessary.
3) Abundance & size - the number of individuals per species is tallied in 5cm size class increments up to 35cm using visual estimation of fork length. If an individual is greater than 35cm, then an estimate of the actual fork length is recorded.
4) Photos - individuals too difficult to identify or unique in some manner may be photographed for later clarification.
Data Caveats: Site selection is different from prior Caribbean Coral Reef Ecosystem Monitoring Program (CCREMP) data collection. This data set is the first time a sampling frame has been used to do site selection. CCREMP surveys (2000-2011) had stations on hard- and soft- bottom habitats; this dataset is from hardbottom sites only. CCREMP surveys were conducted only in the northeast portion of St. Croix; primarily waters less than 30 m from Green Cay to Point Udall. This dataset reflects surveys from hardbottom habitats in waters less than 30m around the entirety of St. Croix.