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AN UNDERWATER VISUAL CENSUS METHOD FOR FAST MAPPING OF LARGE AREAS Alen Soldo 1*, Igor Glavicic 1, Marina Mašanovic 1 and Jelena Kurtovic Mrcelic 2 1 Department of Marine Studies, University of Split, Croatia - [email protected] 2 Public Institution Sea and Karst, Split, Croatia Abstract Traditionally used methods are not useful for precise mapping of growing number of anchor and mooring sites. Thus, this paper describes an easy to use and low cost method for precise fast mapping of large underwater shallow coastal habitats using direct observation and video documentation obtained by using diver propulsion vehicle and georeferencing. Keywords: Mapping, Adriatic Sea, Instruments and techniques, Habitat Human impact and ecological stresses are causing the loss of many coastal (which data were recorded by video cameras) were mounted on DPV. habitats with subsequent impact upon fisheries and the environment. In many Georeferencing was obtained by using GPS device mounted on a surface buoy areas it is already evident that coastal marine biodiversity is decreased as a and connected to the DPV with line (Fig. 1). Time on diving watch was adjusted consequence of the biotic and abiotic changes resulting from anthropogenic to the GPS time for further precise combining of a video and GPS positioning activities. Touristy countries are having a particular problem as tourism is data. In order to minimize the effect of the buoy line curvature on a precision of growing industry which is resulting with the marine environment accessible to GPS data the maximum length of a line always corresponded to previously the tourist use constantly spreading. Within tourism industry nautical activities determined maximum depth. Hence, the diver was constantly winding a buoy are very dependent on environmental quality, and any deterioration in the line on a reel in order to maintain vertical angle of a line to surface as much as marine ecosystem will have a negative impact on it, as well as tourism in general. possible. Analysis of obtained data and their comparison with accessible On the other hand, recreational boating and other related activities are negatively orthophoto images showed that the line curvature didn’t significantly impacted impacting coastal habitats due to the physical damage to the environment caused georeferencing, probably due to the protocol used and shallow water that rarely by anchorage or wave generation, antifouling paints and hydrocarbons releases exceeded 20 m of depth. All the data were analysed and processed within 24 and other oil residues, black water or sewage, garbage and other waste generated hours after the dive which resulted with maps of areas indicating marine habitats onboard, grey water from all onboard aqueous washings and operations, noise according to EUNIS habitat classification, EU Habitats Directive and Croatian disturbances and introduction of non-indigenous species. Such impact is National Classification of Habitat – NCH (Fig. 2). particularly expressed in islands areas due to the insufficient regulation and difficult control. In order to assess these effects it is essential to know an initial state of the habitat and to monitor underwater environment regularly. However, most of anchor and mooring sites are large in surface and distant from the coast and necessary facilities which makes the use of traditional SCUBA divers methods difficult, time consuming and cost intensive. Hence, aerial and satellite monitoring has limited discriminatory ability in mapping fine-scale substrate mixes, while acoustic methods and use of AUV and/or ROV could provide higher resolution data, but their use in obtaining species specific data is very limited [1]. Thus, there is ongoing need to develop an easy to use and low cost method for precise fast mapping of large underwater shallow coastal habitats. As for the purpose of mapping 29 Natura2000 sites selected as future anchor and mooring sites in Central Eastern Adriatic one of the requests was obtaining data on the presence of protected species it was obvious that the method should use divers for precise species identification [2]. However, as the autonomous diver is restricted by the amount of breathing gas that can be carried, and consequently the surface that can be mapped, authors decided to use Diver Propulsion Vehicle (DPV), commonly known as underwater scooter. DPVs are useful for extending the time and distance range of a diver as well as being capable to carry different accessories useful for the research. Fig. 2. An example of a map produced by survey method. Obtained data on distribution and abundance of marine plants and animals, including a presence of protected species, showed that this method, based on direct observations and video documentation, is capable to map marine habitats with sufficient data for initial assessment as well as for a further effective management. The method itself is fast, low coast and it can be performed by a wide population of divers which is of the outmost importance for assessing and monitoring of a many anchor and mooring sites which number is constantly rising. References 1 - Coggan, R., Populus, J., White, J., Sheehan, K., Fitzpatrick, F. and Piel, S. (eds.) 2007. Review of Standards and Protocols for Seabed Habitat Mapping. MESH. 2 - Soldo, A. and Glavicic, I. 2017. A comparison of three techniques for underwater visual sampling of fish communities. Demat'17 (eds. Takagi, T. & Paschen, M.). Contributions on the Theory of Fishing Gears and Related Fig. 1. 1-DPV, 2-buoy line, 3-buoy with GPS. Marine Systems Vol. 10. Therefore, during the survey, two video cameras (one with wide angle lens and one with ability to zoom), one photo camera, diving computer and diving watch 273 Rapp. Comm. int. Mer Médit., 42, 2019.

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