Spatial indicators of fishing pressure: preliminary analyses and possible developments

Ecological indicators of fishing pressure in space are an important part of the Data Collection Framework (DCF) established by the European Commission in its attempt to apply an ecosystem approach to fisheries. These indicators are devised to use the information provided by the Vessel Monitoring System, a mandatory tool for EU fishing vessels which allows to record fishing activity in space and time. This study reports and analyzes trends of DCF fishing pressure indicators in the years 2007--2010 for the Italian trawlers in seven Mediterranean geographic sub-areas and the related trends of landing per unit effort. In addition, new versions of these indicators are developed and their performances compared to the DCF ones by a simulation approach. The rationale for these new version of indicators is based on: (i) the development of a formal definition of ``fishing ground'', allowing for innovative statistical analyses of fishing patterns in space and time; (ii) the revision of issues affecting DCF indicators. Results provide: (i) the first extensive documentation of space use by fisheries through time; (ii) evidences of subtle yet significant changes in fishing pattern which, in agreement to other studies, indirectly support a decline of fisheries resources in the Mediterranean; (iii) improved versions of DCF fishing pressure indicators, obtained via the identification and analysis of fishing grounds and the assessment of aggregation by Gini's G index. The latter point could mark an important progress in order to overcome some critical weakness evidenced by DCF indicators. Moreover, the statistical identification and analysis of fishing grounds could represent a valuable insight in quantitative investigations of fisheries impacts and effects, even beyond indicators computation.