Bottom trawling affects trophic niche diversity of red mullet in muddy bottoms of the Mediterranean continental shelf

Abstract

Bottom trawling causes detrimental effects on marine ecosystems, and significantly alter benthic communities, potentially affecting the diet and trophic role of benthic feeders. The ban on bottom trawling is a common spatial fishing restriction that has been implemented in tropical and temperate regions to restore overexploited marine resources and ecosystems. In northern Sicily (central Mediterranean Sea) two trawl ban areas, the Gulf of Castellammare and the Gulf of Patti, were established in 1990. In both gulfs, the red mullet Mullus barbatus, a commercially important demersal fish and benthic feeder main target of bottom trawlers, has since experienced an impressive increase in biomass. We investigated the stomach contents, prey selectivity, and trophic position (using carbon and nitrogen stable isotope analysis) of red mullet in the two untrawled gulfs and compared the results with two trawled gulfs. Our results show that bottom trawling affects the diet and trophic position of red mullet following the trophic erosion process. In untrawled areas, the species feeds in a less disturbed and well-structured benthic community at a higher trophic position, while in trawled areas it benefits from the more opportunistic epibenthic fauna associated with trawling-induced resuspension of organic matter.

Keywords: Fishing impact; Food web; Trawl exclusion; Trophic ecology; Trophic level.