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Diet and trophic position of deep-sea sharks in the southwest coast of Portugal using Stable Isotopes Analysis and Nucleic Acids Ratios (RNA/DNA).

Goal: Deep sea sharks perform a valuable ecological function maintaining the balance of food webs that support fisheries. However, they are heavily impacted by sustained commercial fishing pressure and little is known about the impacts of the removal of these species from the deep-sea environment. Knowledge of the diet, trophic position and movement patterns of species have long been recognized as critical factors to successfully implement proper management and conservation measures. Thus, this study aims was to assess the ecophysiological condition, diet and trophic position of deep-sea sharks from the southern-west coast of Portugal combining non-lethal approaches. R/D analysis was performed to evaluate the ecophysiological condition while carbon (δ13C: 13C/12C) and nitrogen (δ15N: 15N/14N) stable isotope analysis (SIA) were used to access dietary and trophic position information. Specifically, the aims of this study were to:
• Assess the nutritional condition of sharks using R/D ratios;
• Identify the main preys and quantify its importance to sharks’ biomass using SIA;
• Determine the trophic niche overlap between shark species;
• Determine the sharks’ trophic position.
This was done with the intention to contribute to fill the extant gap and improve the knowledge on the deep-sea sharks from the southwest coast of Portugal.

Date: 1 October 2017 - 1 August 2018

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Sofia Graça Aranha
added an update
The present study combined, for the first time, stable isotopes and nucleic-acid derived indices (non-lethal approaches), to investigate the trophic ecology and ecophysiological condition of seven deep-water shark species off the southwest coast of Portugal: Centrophorus squamosus, Centroscymnus crepidater, Deania calcea, D. profundorum, Etmopterus pusillus, Galeus atlanticus, and Scymnodon ringens. According with the results, these sharks occupy high trophic positions in the local marine food webs, feeding on bathyal teleosts and bathy-demersal crustaceans. Because most of the prey assimilated perform diel vertical migration movements, this study indicates that sharks rely on a strong vertical connectivity between habitats at different depths. Also, our preliminary approach suggests that most sharks were in an overall adequate nutritional condition. Moreover, species targeted by crustacean bottom trawl fisheries, the shrimps Aristaeomorpha foliacea and Aristaeopsis edwardsiana, were heavily assimilated by S. ringens and by small-sized D. calcea individuals (up to 70%), suggesting that these species may be at a higher risk of being captured during fishing activities due to the apparent overlap between fishing grounds and their foraging grounds, raising concern over the impacts on these species.
 
Sofia Graça Aranha
added an update
On this field trip, that took place 20-Feb, all data from the crustacean bottom trawler was collected and it was found 7 different species of sharks from up to 1,400 m depth. Muscle tissue was collected from crustaceans, cephalopods and teleosts in order to analyze the 13C and 15N signature.
 
Sofia Graça Aranha
added an update
The original location of the study, the Southern coast of Portugal, Algarve region, had to be moved to the Southern-west coast of Portugal, leaving from the Sines fisherman's port due to the weather and the fishing boat's port logistics.
 
Sofia Graça Aranha
added a project reference
Sofia Graça Aranha
added a project reference
Sofia Graça Aranha
added a project goal
Deep sea sharks perform a valuable ecological function maintaining the balance of food webs that support fisheries. However, they are heavily impacted by sustained commercial fishing pressure and little is known about the impacts of the removal of these species from the deep-sea environment. Knowledge of the diet, trophic position and movement patterns of species have long been recognized as critical factors to successfully implement proper management and conservation measures. Thus, this study aims was to assess the ecophysiological condition, diet and trophic position of deep-sea sharks from the southern-west coast of Portugal combining non-lethal approaches. R/D analysis was performed to evaluate the ecophysiological condition while carbon (δ13C: 13C/12C) and nitrogen (δ15N: 15N/14N) stable isotope analysis (SIA) were used to access dietary and trophic position information. Specifically, the aims of this study were to:
• Assess the nutritional condition of sharks using R/D ratios;
• Identify the main preys and quantify its importance to sharks’ biomass using SIA;
• Determine the trophic niche overlap between shark species;
• Determine the sharks’ trophic position.
This was done with the intention to contribute to fill the extant gap and improve the knowledge on the deep-sea sharks from the southwest coast of Portugal.