Use of MEDITS trawl survey data and commercial fleet information for the assessment of some Mediterranean demersal resources

Abstract

An assessment of the state of the fisheries of hake, red mullet and Norway lobster was carried out by using trawl survey data from the MEDITS research programme. The assessment was performed by means of the application of a composite model utilising the total mortality rate Z as a direct index of fishing effort. The studied area covered the whole western Italian coast (Ligurian and Tyrrhenian seas) and the eastern coasts of Corsica. The area was divided into twelve sub-areas, considered to be of similar ecological characteristics with similar initial productivity but considered to experience different rates of exploitation. Available information on fishing fleets and their geographic distribution was used in creating sub-areas. For each one of these sub-areas, the total mortality rates and a mean catch per unit of effort were estimated. The estimation of Z was performed by analysing the size structure of the cumulated catch in each sub-area and for each year. Catch rates were estimated as the mean catch per one hour of tow. The positioning of the current values of Z for the different sub-areas relative to the Z at maximum biological production suggests that, in most of the sub-areas, hake is in general fully exploited and red mullet overexploited. In the case of Norway lobster, it was not possible to obtain a statistically acceptable result probably due to a lack of contrasting enough levels of fishing pressure among sub-areas. The results obtained for hake and red mullet are in good agreement with the available information on the consistency of the fleets operating in the different sub-areas.