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Unwanted catches of trawl fisheries: ecosystem effects and advances to an integrated management approach in the Mediterranean

Periodic Reporting for period 1 - FishMan (Unwanted catches of trawl fisheries: ecosystem effects and advances to an integratedmanagement approach in the Mediterranean)

Reporting period: 2017-06-01 to 2019-05-31

Humans have profoundly impacted Earth's ecosystems to the extent that we have generated a new geological era, the Anthropocene. Despite an ancient and profound link between humans and the sea, one of the main attributes of this era is the human impact on marine ecosystems. The sea provides us with food and overall contribute to human well-being. In this context, there is an urgent need to address the environmental effects of human activities to maintain healthy marine ecosystems, and attaining sustainable fishing is a priority in the political agenda. This urgent issue was partly addressed in the 2014 Common Fisheries Policy by the introduction of the Landing Obligation. The CFP considered the reduction of unwanted catches of European fisheries as a matter of priority. However, at that moment, there was little evidence on the effects of the new normative on marine ecosystems but also on the fisheries sector. FishMan project adopted a multi-disciplinary approach to assess potential effects of the Landing Obligation on Mediterranean socio-ecological fisheries systems, and explored alternatives for sustainable fisheries. The project combined data sources of different nature from a NW Mediterranean case study: from basic ecological knowledge on benthic communities from fishing grounds, to fishermen perception on alternative sustainable paths of the sector. Four main objectives were proposed to cover the different angles of the fisheries sustainability problem: i) the assessment of biological assemblages’ vulnerability to trawling; ii) a size-spectra model to explore the ecosystem consequences of fisheries selectivity measures; iii) a framework to monitor the ecological and socio-economic sustainability of a fishery system; iv) incorporation of fishermen perception on management and feedback on sustainable alternatives; v) exploration of wider societal perception on marine and coastal areas in the Mediterranean. The research activities undertaken to achieve these objectives shed light on the state of the fisheries system in the case study, with loss of the most vulnerable marine species due to increased fishing intensity and an important socio-economic impact on local fisheries; however, positive results suggested alternative fishing practices that could reduce ecosystem disturbance while having minimal socio-economic impacts on fishermen.
Research activities, planned to achieve FishMan objectives, largely relied on existing data on benthic communities and fisheries from the NW Mediterranean. The first activity was the assessment of demersal assemblages´ vulnerability to trawling, specifically focusing on the catch of the organism by fishing nets, on potential survival after discard practices and on population resilience to individuals’ catch. This assessment framework was tested in four case studies in southern European Seas, evidencing overexploited communities dominated by highly resilient assemblages, that is, the most vulnerable species have sharply declined or even disappeared from fishing grounds. This work (de Juan et al., 2020; https://doi.org/10.3389/fmars.2020.00044) also evidenced variability in demersal assemblage composition by depth and habitat type, which indicates the importance of spatial restrictions of trawling activities to protect the most vulnerable areas. The second activity aimed at developing an integrative framework for the assessment of the sustainability of the fisheries sector in the Mediterranean. As a result, a multidisciplinary indicator framework encompassed key ecological, social and economic aspects of the trawl fishery that indicated deviance from sustainability of the sector. This framework was successfully tested in a NW Mediterranean trawling fleet and is a promising tool for the monitoring of an effective implementation of an ecosystem-approach to management (Christou et al. 2019; https://doi.org/10.3389/fmars.2019.00594). The third task focused on adopting an Ecosystem Services approach to assess the human-nature interactions in coastal systems. A novel methodological approach was developed (Ruiz-Frau et al., 2020; https://doi.org/10.1016/j.ecoser.2020.101176) for an objective evaluation of cultural ecosystem services demand in marine and coastal areas through the analysis of social media data. Social media (e.g. Instagram and Twitter) provides large data sets on peoples’ posts that inform on activities (e.g. recreational fishing, seafood consumption), places or feelings (e.g. happiness, environmental concern) regarding a natural space (Ruiz-Frau et al., 2020; arXiv:2006.12495v1; de Juan et al., 2020; arXiv:2007.14308v1). The fourth activity resumes an ecosystem-approach to the un-sustainable fisheries problem by exploring the application of a size-spectra model to benthic ecosystems from trawling grounds. The advantage of this approach is the adoption of a species’ size focus, as species’ interactions are highly size-dependent; therefore, fisheries’ selectivity is a significant driver of marine communities’ structure and composition. This model, that was developed in close collaboration with scientists from the University of York (UK), illustrated ecosystem-wide affects of increasing the fishing net selectivity in a NW Mediterranean fishery (i.e. continental shelf trawl fishery targeting hake and red mullet). The last activity had to be largely modified due to COVID pandemic restrictions, as it relied on face-to-face interviews with fishermen and fisheries stakeholders’ workshops planned towards the end of the project. Fishermen interviews collected before the lockdown were complemented with telephonic remote interviews with fisheries stakeholders and local consumers aiming to obtain an ample perspective on perceptions and solutions towards the fisheries sustainability problem. Data gathered still needs to be processed, but a publication that illustrates fisheries actors’ perception on current management and on future sustainable paths is expected to be finalised by the end of 2020.
Trawling activities are mainly driven by fishermen decisions on where to fish, market demands and fishing regulations. But the ecological condition of benthic ecosystems feedback on fishermen through their ability to provide catch. In this complex interacting matrix, small decisions such as fishing over certain habitats, discarding fractions of the catch, or increasing effort can have significant effects through the system, with ultimate returns to the fishermen through profits. FishMan embraced a novel research approach in trawl fisheries science by focusing on a socio-ecological framework. The traditional assessment of ecosystem impacts of fisheries, relying on biological communities composition and structure, was complemented with a size-spectra approach that is foreseen to have significant impact in fisheries science as predictions on the effects of fishery restriction measures are better adjusted to size-dependent interactions in a biological system. Furthermore, the efforts to incorporate the human dimension in fisheries’ research implies FishMan results are applicable to real-world scenarios, as incorporating the perception of fisheries stakeholders on current problems and potential solutions is essential for effectively advancing towards an ecosystem-based approach.
Commercial trawler fishing net