Analysis of trawling catch composition during different fishing intensity periods in two Mediterranean demersal fishing grounds
The study was carried out in two different fishing areas of the continental shelf: one in the Adriatic Sea (central Mediterranean) and the other in the Catalan Sea (western Mediterranean). Information on the characteristics of the fishing fleets and on the fishing effort was collected in both areas. Sampling on board otter trawlers was performed from November 2002 to December 2003 in the Catalan Sea and from February 2003 to January 2004 in the Adriatic Sea. The Ecological Use Efficiency (EUE) index was applied to evaluate the impact of trawling on the demersal fish assemblages. The Adriatic fishing ground was affected by high fishing intensity from January to June, while the Catalan area was affected from September to February. In the Adriatic Sea, fishing activity was closed for 45 days while in the Catalan Sea for 62 days both in summer. Totals of 92 and 88 species were collected in the Adriatic and Catalan fishing grounds respectively. The species composition of the retained and discarded fractions showed close agreement between the two areas. Merluccius merluccius and Mullus barbatus showed very low discard rates in both areas, as well as Citharus linguatula in the Catalan Sea and Arnoglossus laterna in the Adriatic Sea. However, Liocarcinus depurator was characterized by large discard fractions. In both fishing grounds Squilla mantis showed high catch rates with low discards, except in March in the Catalan Sea. The main conclusion drawn from this study is that the maximum commercial yields are obtained after the fishing closure in both areas, then the commercial yields progressively decrease in the following months. The EUE index shows that the proportion of the discarded fraction was slightly higher in the periods of low fishing intensity, with similar values in both areas.
The Electronic Atlas is an exhaustive cartography of the spatial-temporal distribution of the fishing effort in the appropriate study Areas (ASA) using different tools to estimate the fishing effort by direct and indirect way. In the Mediterranean ASAs the effort estimation was achieved on board the vessels and by daily vessel’s registers at the local auction, combined with fishermen interviews. In the North and Irish Sea fishing effort was estimated via Vessel Monitoring System VMS and over-flight data collected by local fisheries authorities. In a parallel way, the effort was estimated by means of an indirect method counting side scan sonar trawl tracks. Atlas CD contains two elements: TNTAtlas, that is an easy-to-use free map viewer, and the maps themselves. TNT Atlas provides an interface that allows users to navigate around maps, zoom in and out, activate/deactivate layers for better vision, consult databases associated to map elements (points, vectors&) and calculate areas, distances, etc directly on maps. This viewer is automatically installed on user’s HD the first time Atlas CD is loaded. Once the viewer has been installed, user can load Atlas from a single .atl file directly on CD s root when needed. Contains of CD can be copied to HD in order to improve visualization speed, the only requirement is to maintain original folder names and hierarchy. Internal organization of Atlas has been designed in order to allow user navigate freely across different maps but always inside a single study zone, to prevent accidental losing of geographical orientation. Besides, all zones have a common design (same color for terrain, similar gradient bars, same legend type&) in order to show an integrated external aspect. All maps are georeferenced in WGS84 Datum. Navigation: When Atlas is loaded, Home Level screen appears showing a map of Western Europe with a tridimensional representation of Ocean Relief. User can choose one of four study zones (north Sea, Irish Sea, Catalan Sea and Adriatic Sea) by clicking on their geographical position with Hyperindex Navigation tool activated. In this screen there is also a title bar with direct links to Response web site and help files. These help files will be always accessible to user a click away from navigation bar.
Functional changes as indicators of trawling disturbance on benthic community from a fishing ground (NW Mediterranea)
Trawling activities disturb benthic communities eliminating the most vulnerable organisms and modifying the habitat structure. Further implications of commercial trawling activities are poorly understood, however various studies suggest that chronically disturbed communities are dominated by opportunistic organisms. This study focuses on a chronically disturbed community from a fishing ground to study the implications of commercial trawling on the functional traits of the benthic community. The trawling ground is located in the NW Mediterranean, and includes an area that has not been fished in twenty years. Both fished and undisturbed areas were compared analysing the functional traits of the infaunal and epifaunal communities. Results showed that the overall benthic community from the fishing ground is mainly composed by epifaunal burrowing deposit feeders and predators, and deep burrowing infaunal deposit feeders. The comparison of both areas highlighted that the fished area had significantly higher abundance of large burrowing epifaunal scavengers and mobile burrowing infaunal organisms. On the contrary, the undisturbed area was characterised by significantly higher abundance of more vulnerably surface organisms, such as sedentary suspension feeders. The relevance of this study is highlighted as an opportunity to investigate functional components of a benthic community from a fishing ground, and analyse how the community respond to trawling activities. We suggest that fisheries managers aiming to reduce ecosystem disturbance must consider the implications of trawling on the structure and functioning of the communities.