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.
Benthic infauna from grab samples - Irish Sea
Abundance 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.xlsx
Otter trawl catches - Irish Sea
The 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.csv
D13C and D15N - Irish Sea
Stable 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.csv
D13C and D15N - Kattegat
White 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.csv
Nephrops length weight - Irish Sea
Nephrops 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.csv
Irish Sea otter trawl and grab positions
Latitude and longitude of the station sampled in the Irish Sea
DOI: http://dx.doi.org/10.5061/dryad.04dv4
The 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
