Data on demersal and mega-benthic species were sampled in the context of the MEDITS suveys carried out on the Sanish Mediterranean continental shelf since 1994. MEDITS is a program of bottom trawl surveys developed annually in the Mediterranean, in which all the participants use the same gear, sampling protocol and methodology, with the objective to evaluate the abundance and distribution of stocks, independently of the data provided by commercial fisheries, and to assess the impact of the fishing activity on the environment.
A protocol exists to be applied, which is reviewed and adapted during the annual coordination meetings. This protocol includes the design of the survey, the sampling gear (feature and handling), the information collected and the management of the data. MEDITS surveys are currently conducted by eleven Mediterranean countries (Albania, Croatia, Cyprus, France, Greece, Italy, Malta, Montenegro, Morocco, Slovenia and Spain), within the European Commission framework for the collection, management and use of data in the fisheries sector and support for scientific advice regarding the common fisheries policy (Data Collection Multiannual Program), with the financial support from the DG MARE and Member States.
In Spain, the MEDITS surveys are developed annually from April to June, on board the R/V Cornide de Saavedra (1994-2013) and the R/V Miguel Oliver (2014-2017), along the infralittoral, circalittoral and bathyal soft bottoms off Mediterranean Iberian Peninsula and the Balearic Islands (Geographical Sub-Areas GSAs of the General Fisheries Commission for the Mediterranean GFCM 1, 2, 5 and 6) between 30 and 800 m depth. As the other MEDITS areas, and following the MEDITS protocol, it is applied a stratified random sampling, taken into account five depth strata (30-50, 51-100, 101-200, 201-500 and 501-800 m) and the four Geographical Sub-Areas (GSA) established by the General Fisheries Commission for the Mediterranean (GFCM) in the area: 1 and 2 (Northern Alboran and Alboran Island, respectively), 5 (Balearic Islands) and 6 (Northern Spain). The bottom trawl hauls are performed during daylight, with an effective duration (from the arrival of the gear to the seabed until its departure) of 30 and 60 minutes, depending on the depth (<200 and >200 m, respectively) and the speed is around 3 knots. The sampling gear is a bottom trawl made of four panels, referenced as GOC73, with 10 mm of mesh side in the codend and doors of type Morgére, with 2.5-3 m vertical opening and 16-22, horizontal opening. SCANMAR system is used in each haul to estimate its effective duration and the geometry of the net. Moreover, a CTD SBE-37 is attached to the flotsam of the net to record temperature and conductivity of the water above the seafloor during the haul. On board the vessel, the catches are split into the categories and sub-categories, according the MEDITS protocol, and the total weight and number of individuals is collected. The common coding system adopted for the complete set of species is a RUBIN like coding system as defined in the NCC standard, even if this international coding system has been no longer maintained for some years. This coding system appears to be a very practical one and it would be very easy in the future to build a correspondence table with any new coding system. In respect to the NCC recommendations and as the MEDITS coding is not strictly identical to the RUBIN one (different use, species not referenced to in the RUBIN code), the "name" of this code has been changed and is for the purpose of the MEDITS called "FM list". The species identifications are made following Fisher et al. (1987). For the fish species not included in this work, the descriptions from Whitehead et al. (1984) have been used. Since 2012, the MEDITS reference list includes 82 target species. For all these species, the total number of individuals, the total weight and the individual length should be collected. This list has been further split in two groups: (i) MEDITS G1 includes 41 species with 9 demersal (3 fish, 4 crustaceans and 2 cephalopods) and 32 chondrictians, for which the total number of individuals, the total weight, the individual length and also biological parameters including sex, maturity (according to , individual weight and age (age has been proposed only for the teleosts of the Group 1) should be collected; and (ii) MEDITS G2 includes 43 species for which only total number of individuals, total weight and individual length should be collected. Standard formats are defined for the data storage and to facilitate the exchange of the data produced by the MEDITS surveys. The exchange files are in “*.csv” format, using semicolon as field separator. Four file types are defined in order to store and exchange the data: (Type A) characteristics of haul; (Type B) catches by haul; (Type C) length, sex, and maturity at aggregated level; and (Type E) age, weight and maturity by length at individual level. For more detailed information: MEDITS-Handbook. Version n. 8, 2016, MEDITS Working Group: 120 pp.