The use of Mean Life Span index as indicator of ecological status in trawled areas: Preliminary observations

The development and monitoring of ecological indicators play a prominent role for supporting the implementation of an ecosystem approach to fisheries by assessing ecosystem status. Different approaches have been used to build indices on the impact of fishing, in particular for bottom trawling. In this study the Mean Life Span index was used in two areas on historical series of trawl survey data aiming at understanding pros and cons of the use of this index and his applicability in a Mediterranean context. The study was carried out in the Gulf of Castellammare, an area subject to trawl ban since 1990 and in a portion of the Strait of Sicily, an extremely important area for trawl fisheries. The Mean Life Span index was applied at the two Mediterranean historical data-set and the values ranged from 6.1 to 11.01. Its applicability depends on the availability of data on the life cycle of the species, in particular on maximum age. If this data are scanty, its application is poorly indicated. Results obtained in the two study areas showed a slightly increasing trend across years. This could be related to the trawl ban in the Gulf Castellammare and to a decrease of fishing pressure in the Strait of Sicily.