DOI: 10.5061/dryad.g3qh8
title: Data from: Stable isotopes reveal the effect of trawl fisheries on the diet of commercially exploited species

description: Bottom trawling can change food availability for benthivorous demersal
 species by (i) changing benthic prey composition through physical seabed
 impacts and (ii) by removing overall benthic consumer biomass increasing
 the net availability of benthic prey for remaining individuals. Thus
 trawling may both negatively and positively influence the quantity and
 quality of food available. Using δ13C and δ15N we investigated potential
 diet changes of three commercially exploited species across trawling
 gradients in the Kattegat (plaice, dab and Norway lobster (Nephrops)) and
 the Irish Sea (Nephrops). In the Kattegat, trawling affected primarily the
 biomass of benthic consumers, lowering competition. Nephrops showed
 significant positive relationships for δ13C and a domed relationship for
 δ15N with trawling. In the Irish Sea, intense trawling had a negative
 effect on benthic prey. δ13C and δ15N thus showed the inverse
 relationships to those observed in the Kattegat. Plaice from the Kattegat,
 showed a significant relationship with trawling intensity for δ13C, but
 not for δ15N. No relationship was found for dab. Changes of δ13C and δ15N
 correlated with changes in condition of species. The results show that the
 removal of demersal competitors and benthos by trawling can change the
 diets of commercial species, ultimately affecting their body condition.
description: Benthic infauna from
 grab samples - Irish SeaAbundance and biomass of
 benthic invertebrates from the Day grab samples per species and per
 station. Benthic invertebrates were sampled by taking six 0.1 m2 grabs at
 haphazard locations within the station box. All samples were sieved and
 preserved in 4% formalin for identification. All invertebrates were
 identified to the highest practicable taxonomic resolution (mostly genus
 or family) and the wet weight of species was estimated after
 blotting.Benthic infauna_Irish
 Sea.xlsxOtter trawl catches -
 Irish SeaThe catch composition of
 all species per trawl for the otter trawl catches. One or two tows of 30
 min were carried out at each station with an otter trawl (distance across
 mouth of the net 16 m, 82 mm diamond mesh cod-end) at a speed of 3 knots
 between 06.00h and 17.00h. The total catch number and weight per species
 was measured.Otter trawl catches Irish
 Sea.csvD13C and D15N - Irish
 SeaStable isotope δ13C and
 δ15N signatures for Nephrops from the Irish Sea. White muscle tissue was
 extracted from the first tail segment with shell, digestive and nerve
 tract removed. Nephrop samples were stored frozen at -18°C after capture
 for later analysis in the laboratory. In the laboratory all tissue samples
 were oven dried for 24 hours at 75°C. Each individual tissue sample was
 ground to a homogenous powder using an agate pestle and mortar.
 Subsequently, 1.5-2.0 mg of the resulting powder was weighed into tin
 capsules for stable isotope analysis. Tissue samples were combusted for C
 and N isotope compositions using continuous flow isotope ratio mass
 spectrometry (CF-IRMS) THERMO delta X PLUS mass spectrometer (Scientific
 Technical Services - University of the Balearic Islands). The isotope mass
 spectrometer was operating in dual mode measuring δ15N and δ13C in the
 same sample Additionally C/N ratios are provided.Isotope data_Irish
 Sea.csvD13C and D15N -
 KattegatWhite muscle tissue
 samples from 5-6 individuals of each respective study species were
 collected for each station. For the flatfish, a 2 x 2 cm piece of white
 muscle tissue was taken with the skin removed approximately 2 cm to the
 right of the pectoral fin and 1 cm above the lateral line. For the
 Nephrops, white muscle tissue was extracted from the first tail segment
 with shell, digestive and nerve tract removed. Due to logistical
 constraints of the sampling, all samples from t were preserved in 100%
 pure ethanol for transport to the laboratory. In the laboratory all tissue
 samples were oven dried for 24 hours at 75°C. Each individual tissue
 sample was ground to a homogenous powder using an agate pestle and mortar.
 Subsequently, 1.5-2.0 mg of the resulting powder was weighed into tin
 capsules for stable isotope analysis. Tissue samples were combusted for C
 and N isotope compositions using continuous flow isotope ratio mass
 spectrometry (CF-IRMS) THERMO delta X PLUS mass spectrometer (Scientific
 Technical Services - University of the Balearic Islands). The isotope mass
 spectrometer was operating in dual mode measuring δ15N and δ13C in the
 same sample. Additionally C/N ratios are provided.Isotope
 data_Kattegat.csvNephrops length weight -
 Irish SeaNephrops norvegicus
 length and weight data that was used to estimate their condition. The
 carapace length and the total weight was measured, and their sex recorded.
 Futhermore if females carried eggs. Note that body weight is clawless
 weight.Nephrops_length_weight_Irish
 Sea.csvIrish Sea otter trawl
 and grab positionsLatitude and longitude
 of the station sampled in the Irish SeaDOI:
 http://dx.doi.org/10.5061/dryad.04dv4The data presented in
 the publication from the Kattegat, except for the isotope (see above),
 data can be found in Dyrad associated to an earlier publications by the
 authors: Data from: Bottom trawling affects fish condition through changes
 in the ratio of prey availability to density of competitors Hiddink JG,
 Moranta J, Balestrini S, Sciberras M, Cendrier M, Bowyer R, Kaiser MJ,
 Sköld M, Jonsson P, Bastardie F, Hinz H Date Published: May 31, 2016 DOI:
 http://dx.doi.org/10.5061/dryad.04dv4 To access the Kattegat data please
 use the following link
 http://datadryad.org/resource/doi:10.5061/dryad.04dv4