Search

Abstract Demersal and benthivorous fish depend on prey availability in benthic habitats for their diet. Prey availability may in turn be affected by bottom trawling. Our study attempted to link the prey consumed by fish directly to those available in the benthic environment. We test the hypothesis that bottom trawling significantly affected the trait composition of fish diets with a strong link to benthic habitats. Stomach content data were analysed for seven demersal and benthivorous fish species in the southern and central North Sea and were related to habitat fauna collected by grab and epi-benthic trawl data across the same spatial extent. Biological trait analysis was used to avoid taxonomic bias in large-scale comparisons across habitats and to quantify the effect of bottom trawling, which tends to shift prey diversity in favour of small, opportunistic and short-lived species and traits. The diets of two demersal omnivores (whiting, Merlangius merlangus and Atlantic cod, Gadus morhua) and two opportunistic benthivores (haddock, Melanogrammus aeglefinus and long-rough dab, Hippoglossoides platessoides) did not appear to reflect either infaunal or epifaunal traits that were abundant in the benthic environment. The diets of European plaice (Pleuronectes platessa) and Dover sole (Solea solea), however, showed strong links with infaunal prey trait composition in shallow sand to muddy sand habitats located in the eastern North Sea and the Dogger Bank. Such strong links were also observed for the diets of Common dab (Limanda limanda) and plaice in similar habitats in deeper waters. Plaice targeted small to medium sized infaunal burrowers and deeper dwelling infaunal species. Its diet was significantly affected by bottom trawling, which caused a reduction in prey biomass in their stomachs rather than a shift in trait composition. Our study showed that the diets of benthivorous fish across large spatial scales are strongly linked with the prey trait availability in their benthic habitats and that bottom trawling significantly affected the diet of plaice, a species with strong habitat-diet associations. Highlights • Strong links between diet and benthic habitats in three out of seven fish predators. • Similarity in trait composition between infauna and stomach contents is habitat-specific. • Strength of linkage between the diets of sole, plaice and dab and habitats is size-specific. • Bottom trawling significantly affected the biomass of plaice diet but not the trait composition. [ABSTRACT FROM AUTHOR]

Highlights • The effect of trawling activity on two megabenthic species were investigated along the margin of Gioia Canyon. • The abundance of the bamboo-coral Isidella elongata was lower in areas exposed to higher trawling intensity. • Diffuse presence of epibionts on I. elongata suggests stressful conditions related to trawling. • Relatively high abundances of the sea pen Funiculina quadrangularis occurred in areas with intermediate trawling effort. • Vulnerability to bottom trawling can be different for the two species. Abstract The impacts of fishing activities on ecosystems represent an acknowledged environmental issue, especially considering the increasing demands for the conservation of biodiversity. Submarine canyons are complex environments that can harbor high biodiversity of benthic ecosystems and high biomass of fish species, thus representing preferential fishing areas for bottom trawling fleets. The effects of bottom trawling on the benthic epifauna were investigated over the soft-bottom margins of the Gioia Canyon (Southeastern Tyrrhenian Sea) by means of quantitative analysis of Remote Operated Vehicle (ROV) video transects and compared with the recent pattern of trawling intensity, reconstructed through processing of data collected with the Vessel Monitoring System (VMS). Four ROV transects were then performed at 320–540 m depth in areas affected by different trawling pressure. The analysis was focused on the bamboo coral Isidella elongata and the sea pen Funiculina quadrangularis , which are considered indicator taxa of Vulnerable Marine Ecosystems (VMEs) and relevant in terms of sustainable management priorities. I. elongata only occurred at the two deeper stations, below 400 m depth. This species showed a clear relationship with trawling intensity, since its abundance was significantly higher under low trawling intensity, where coexistence of large (>20 cm height) and small colonies was observed. The relatively high prevalence of small colonies in areas exposed to higher trawling effort was interpreted as a consequence of the trawling activity that removed the larger colonies. However, the frequent occurrence of dead colonies and the diffuse presence of epibionts (e.g. the anemone Amphianthus dohrnii and the hydroid Clytia linearis) on living colonies indicate stressful conditions for I. elongata even in areas where trawling intensity was lower. Conversely, the relationship between trawling intensity and species abundance was not straightforward for F. quadrangularis ; despite the lowest abundance of this species was recorded in areas subject to high trawling intensity, relatively high abundances were observed in areas with intermediate trawling effort. Although such distribution may be driven by other environmental factors, it suggests that vulnerability to bottom trawling can be different for the two species. [ABSTRACT FROM AUTHOR]