Database of the location and typology of artificial reefs in the Gulf of Lion (NW Mediterranean Sea)

[Lien vers la fiche source] The Gulf of Lion is a 15000 km² crescent shaped continental shelf located in the northwestern Mediterranean sea which 400 km long coastline extends from Cap Sicié to Cap Creus. It is mainly covered by soft-bottom subtrate extending with a gentle slope from the coast down to 200 m water depth with a few rocky substrates spots of less than 30 km² at the coast (Côte des Albères in the Pyrénées-OrientalesCôte Vermeille, Cap Leucate, in Aude and Cap d'Agde, Côte Bleue and the Calanques) and offshore. The Gulf of Lion (NW Mediterranean Sea), has suffered from intensive and sometimes poorly managed exploitation of fishery resources (trawling in non-regulated areas , juvenile capture, fishing during the spawing season, etc.). The main consequence was a decline in fish resources, leading to a major recession in professionnal fisheries since 1997 (Ifremer SIH 2007). In addition, the area experienced an intensification of coastal urban development and the development of maritimes activities like recreational fishing and sparefishing. The decline of professionnal fisheries and the demand for recreational fishing lead several municipalities to immersing artificial reefs (AR) with the objective of protecting or restoring provisionning services in areas perceived as sensitive or degraded. Some areas of the maritime public domain were conceded to project owners (generally the municipality) for a period of time that can vary from 15 to 30 years for artificial reefs deployments. Artificial reefs deployment effectively covered a small proportion of the surface area of those concessions. However, removal of artificial reefs when the concessions expired has never been done and may conflict with future occupation of the maritime public domain, especially if the information of artificial reefs deployment locations had to be lost, as it is spread among several project owners. Compiling georeferenced data about artificial reefs deployement is essential for future maritime spatial planning and the present database gather these information for a large part of the Gulf of Lion (from the Spanish border to Fos). For more than 40 years, a total of about 800 artificial reefs have been submerged in soft bottom substrate between 10m and 35m water depth along the Gulf of Lion coastline from Saint cyprien to the Gulf of Beauduc, summing up to 32,840m3 of artificial reefs dispersed over 74km² of concessions, most of them having expired. Different phases of immersion can be identified. In 1968, the first experimental immersion took place off the coast of Palavas and included a heterogeneous set of man-made structures (car wrecks, concrete blocks, school tables, etc). In 1985, a large deployment program carried by the Languedoc-Roussillon region, led to the immersion of 14,446 m3 of artificial reefs spread along the coastline of Gruissan, Saint Cyprien, Canet, Port la nouvelle and Agde. The design of these ARs was inspired by those of Japanese ARs: Bonna modules and Comin modules, with the objective of supporting professionnal fishing by adding complexity in soft-bottom areas From 1988 to 1999, new kind of artificial reefs (rocks, pipes, poles) were deployed for protection against illegal trawling, starting in the Gulf of Beauduc and followed by the Gulf of Aigues Mortes and in Agde-Marseillan. Lastly, between 2002 and 2009, a final phase of immersion with dual objectives of protection and production made the site which has already been subject to immersion, such as Agde, Gruissan, Aigues mortes more complex, and new sites such as Valras and Leucate were also created. The dataset compiles the geographical coordinates (WGS 84 Decimal degree) of 763 of these artificial reefs, their type (among the 18 possible types), their dimension (length / height / width / diameter), deployment depth and year, and initial project owner locality. Data were retrieved from all institutional corporations, project managers, companies or professional organizations that contributed to these deploments and scientists that studied artificial reefs since their deployment. A three-level quality index of the AR georeferencing has been added to the databasewith 1 meaning poor quality (no georeferencing control and old immersion plan) / 2 average quality (no georeferencing control and recent immersion plan) / 3 good quality (georeferencing control). Georeferencing was controlled by different means : multibeam echosounder, single beam echosounder, sonar, LIDAR and scuba diving.