WAMSI Node 3.2.1 - Diversity, abundance and habitat utilisation of sharks and rays - Lagoon and reef edge dive survey data

Brief description

Snorkel and SCUBA underwater visual surveys were conducted as part of four field trips to Ningaloo in April and June 2007 and August and December 2008. The June and August surveys were restricted to the reef edge on SCUBA, while the April and December surveys were mainly on snorkel and in the lagoon. While the original intention was to provide coverage through the different seasons, poor weather conditions coincided with most of the planned fieldwork (including cyclone ‘Nicholas’) resulting in re-scheduling of some trips. A total of 137 sites were surveyed between Vlaming Head on the northeast of the Cape to Gnaraloo in the southern part of the Marine Park (see thumbnail picture). Of these surveys, 89 were in sanctuary zones and 48 in non-sanctuary zones (sanctuary zones are shown as hatched in the picture).

Lineage

Statement: Snorkel and SCUBA underwater visual surveys were conducted as part of four field trips to Ningaloo in April and June 2007 and August and December 2008. The June and August surveys were restricted to the reef edge on SCUBA, while the April and December surveys were mainly on snorkel and in the lagoon. While the original intention was to provide coverage through the different seasons, poor weather conditions coincided with most of the planned fieldwork (including cyclone ‘Nicholas’) resulting in re-scheduling of some trips. In the majority of underwater surveys between one and four swimmers were spaced out in parallel, their distance apart based on water visibility, and swam in one direction, usually with the current. The start and finish positions were recorded by GPS, as well as the start and finish times, visibility and depth, enabling a swept area to be calculated. Any elasmobranchs observed were recorded on a datasheet immediately after returning to the surface. In some cases, when GPS positions were not available, the distance swum was estimated or calculated from relationships developed between swim duration and distance for a given number of observers. Sites were chosen to cover major habitat types and different management zones (sanctuary versus non-sanctuary) based on maps provided by DEC, while covering as much of the NMP as possible. Where feasible, each survey was performed on a uniform habitat, but in some cases the habitat was mixed. The different habitat types encountered on a dive were expressed as a percentage of the overall cover. In the lagoon, we mainly operated as two teams working from aluminium dinghys allowing a greater coverage of the Marine Park. A few surveys were conducted from a boat over shallow water when conditions were calm, or from the shore. When multiple divers conducted a survey, the species observed were discussed immediately after leaving the water to reduce the possibility of double counting. A total length for sharks, wedgefish and shovelnose rays (or disc width for all other rays) was estimated for each individual observed and recorded on the data sheet next to the relevant species. Weather was a major factor governing which sites and habitats could be surveyed. Tides and launching sites also influenced the shallower sites and the channel access to the outer reef. Survey data were entered into a spreadsheet every night and any issues or queries about any particular survey were discussed with personnel who undertook that survey. The area swept was calculated as follows: Area swept = Distance swum*number observers*visibility The sightings of each species were expressed as the number of individuals per unit area of 100 m2 (spua).

Notes

Credit
JD Stevens, PR Last, WT White (CSIRO Marine & Atmospheric Research, Hobart) RB McAuley (Department of Fisheries, Government of Western Australia, Perth) MG Meekan (Australian Institute of Marine Science, Perth)