A multi species index (BOI), defined as the ratio between "bottom dwelling fish" and "overall fish" biomasses, was recently proposed as a bio indicator of the status of the demersal fish assemblages. This simple tool is based on the conceptual consideration that trawling first removes the bottom dwelling and less mobile animals from a bottom assemblage; since fish appears the most susceptible group to trawling impact, the index was limited to bony fishes and elasmobranchs. Preliminary analyses, carried out on epibathyal bottoms in three areas in the Strait of Sicily, under different levels of fishing pressure, already suggested that the BOI could be broadly used as a quantitative proxy of the trawling impact on the various demersal assemblages. This paper presents an attempt to evaluate the performance of the BOI on a wider bathymetric range and a larger area. The spatial distribution of the main fish assemblages, the biomass (all fish, decapod crustaceans and cephalopods) indices and the BOI were studied on the bottoms of the Strait of Sicily, including the Italian side up to the median line and the Maltese exclusive fishing zone (MEFZ). The inclusion of the MEFZ yielded information for an area characterized by a modest trawling impact, which is moreover concentrated in just a few fishing grounds. Data were collected during the 2002 MEDITS trawl surveys, carried out in summer on bottoms between 10 m and 800 m. Clustering and multidimensional scaling techniques were applied for studying the fish assemblages. The spatial distribution of the studied variables was assessed using the Kriging interpolation and Thiessen polygons. Each approach produced a very complex picture of the resources in the investigated areas. The BOI, used in association with the representation of the biomass indices, seems able to distinguish areas exploited with lower trawling pressure; these low impact areas are located in the western and eastern edges of the Strait, the latter including most of the MEFZ.

Evaluating the performance of an index of trawling impact in the Strait of Sicily

Gristina M;G Garofalo;F Fiorentino
2004

Abstract

A multi species index (BOI), defined as the ratio between "bottom dwelling fish" and "overall fish" biomasses, was recently proposed as a bio indicator of the status of the demersal fish assemblages. This simple tool is based on the conceptual consideration that trawling first removes the bottom dwelling and less mobile animals from a bottom assemblage; since fish appears the most susceptible group to trawling impact, the index was limited to bony fishes and elasmobranchs. Preliminary analyses, carried out on epibathyal bottoms in three areas in the Strait of Sicily, under different levels of fishing pressure, already suggested that the BOI could be broadly used as a quantitative proxy of the trawling impact on the various demersal assemblages. This paper presents an attempt to evaluate the performance of the BOI on a wider bathymetric range and a larger area. The spatial distribution of the main fish assemblages, the biomass (all fish, decapod crustaceans and cephalopods) indices and the BOI were studied on the bottoms of the Strait of Sicily, including the Italian side up to the median line and the Maltese exclusive fishing zone (MEFZ). The inclusion of the MEFZ yielded information for an area characterized by a modest trawling impact, which is moreover concentrated in just a few fishing grounds. Data were collected during the 2002 MEDITS trawl surveys, carried out in summer on bottoms between 10 m and 800 m. Clustering and multidimensional scaling techniques were applied for studying the fish assemblages. The spatial distribution of the studied variables was assessed using the Kriging interpolation and Thiessen polygons. Each approach produced a very complex picture of the resources in the investigated areas. The BOI, used in association with the representation of the biomass indices, seems able to distinguish areas exploited with lower trawling pressure; these low impact areas are located in the western and eastern edges of the Strait, the latter including most of the MEFZ.
2004
Istituto per l'Ambiente Marino Costiero - IAMC - Sede Napoli
multi species fisheries
trawling impact indicator
demersal assemblages
Strait of Sicily
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.14243/82397
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