Can deep-sea sharks survive – and thrive – in fishing grounds?

  • Rays & Skates
  • Sharks
Years funded
  • 2021
  • Active
Project types
  • Conservation
  • Research
  • The Portuguese Institute for Sea and Atmosphere
  • University of Algarve
  • University of Porto

Sofia is driven by a passion for deep-sea sharks and aims to produce a fishing handling protocol for deep-sea fishermen in Portugal’s southern Mediterranean and Atlantic waters. She developed the DELASMOP project to assess the condition and survival of elasmobranchs caught in fisheries in the North-Eastern Atlantic. Sofia collects vital information about the fishing vessels while aboard deep-sea crustacean trawlers, and also samples the sharks brought in as bycatch. She tags them before release to assess their survival rates, and collects tissue samples to understand their diet, to assess if there is overlap between shark feeding grounds and fishing areas.

Can deep-sea sharks survive – and thrive – in fishing grounds?

Sofia Graça Aranha

Project leader
About the project leader

I grew up in Rio de Janeiro, one of the most dangerous cities in the world, but the sea was where I always felt safe. As a child I used to watch Jacques Cousteau documentaries with my grandmother and I remember being very drawn to the ocean, but I had no concept that it could provide a career for a city girl. It was only when I was in my late teens, with no idea of which career path I wanted to follow, that something ‘clicked’ while I was watching a documentary, and I ended up chasing my childhood dreams...

Project details

DELASMOP: is it possible for deep-sea sharks and rays thrive and survive in fishing grounds?

Key objective

DELASMOP aims at contributing to the conservation of deep-sea elasmobranchs (DSE) by developing a guide with the best fishing procedures and handling practices on board, to decrease the number of DSE caught in crustacean bottom-trawl fisheries while increasing their survival chances after release.

Why is this important

Portugal is the leading country in Europe on seafood consumption (57 kg/person/year), and the South-Southwest coasts are the most important areas for crustacean bottom-trawlers. Unfortunately, the estimated deep-sea elasmobranch (DSE) bycatch in these fisheries is 40%. Although current European legislation requires mandatory discards of most DSE, it is unclear their survival after discarding. This is of great concern since 44%  of DSE in Europe are either endangered or lacking basic ecological and biological information.


The targeted fishing of deep-sea elasmobranchs (DSE), sharks and skates, is prohibited in Europe, but they are still heavily caught incidentally and discarded, especially in the crustacean bottom-trawler fishery (CBT). In Portugal, CBT can have up to 80% of incidental catch and DSE represents 40%. This is of great concern because DSE are amongst the most vulnerable organisms due to increased pressure and decreased temperatures with depth, leading to slower growth rates. This means that overfishing can happen at a higher pace than for other shallow-water species because they simply cannot repopulate quickly after they are overfished. Thus, overexploitation may have profound consequences for some species not only locally, but also globally because some DSE are migratory. Estimating their immediate mortality rates and post-release mortality after being discarded is important because it precludes establishing sound management measures, although, this type of information is costly, technically difficult to obtain and vary greatly among fisheries, habitats, seasons, type of gear, environment, etc. For that reason, the available estimates are disparate and limited to a few numbers of species and fisheries. For instance, for longline fisheries, the immediate mortality rates can vary from 0-100% for DSE, whilst the post-release mortality can be as high as 83% after only 24h of release due to sub-lethal effects.  Likewise, data on the overlap of elasmobranchs and fisheries is also difficult to obtain and scarce. In a recent study with pelagic sharks, it was demonstrated that there is an 80% overlap between sharks’ habitats and fishing areas since sharks select and aggregate in areas with high productivity which are also targeted by longliners. Thus, it is likely that DSE will also occupy habitats based on food availability, and as the CBT operates at increasing depths to maximize catches for revenue, the overlap should also occur.

Aims & objectives
  • To identify the most common deep-sea sharks and skates (DSE) captured as bycatch by crustacean bottom-trawler fisheries (CBT) and relate it with environmental data and operational fishing procedures. We will collect information during routine commercial fishing activities and afterwards, in combination with results from scientific cruises, we will identify the procedures resulting in lower catches of DSE.
  • To evaluate the effect of CBT on the survival of DSE.  Immediate survival rates will be determined on board. Long-term survival rates will be estimated by tagging and releasing live individuals with a system of numbered dart tags.
  • To evaluate the probability of each DSE species to be caught by CBT, by identifying their preferred prey, using non-lethal approaches. We believe that if crustaceans are important contributors to their diet, there is an increased risk of being caught by CBT.
  • To prepare a protocol with the adapted fishing procedures and handling practices to decrease the number of DSE caught by CBT, while increasing their survival chances after release.
  • To organize and conduct participatory meetings with fishermen, fishermen associations, and governmental institutions to identify main challenges and to disseminate the project’s findings on DSE-friendly procedures.
  • Also, to propagate the main findings for the general public through the website, social media and dissemination activities in environmental awareness centres.