The practice of discarding unwanted catch back to the sea is highly criticized by stakeholders involved in fisheries governance, which is per se a complex decision making environment, and many attempts have been made worldwide to tackle the problem (Hall and Mainprize 2005, Pérez-Roda et al. 2019). Estimates of discards are 9.1 million t per year for the period 2010-2014 (Pérez-Roda et al. 2019), although high uncertainty in global discard data over time has been detected (Zeller and Pauly 2005). A recent approach based on reconstructed time series has shown a decrease in discard rates due to the likely adoption of more selective gears and the rising market value for fishmeal (Zeller et al. 2018).

The fisheries management regime in European Union countries stems from the Common Fisheries Policy (CFP). From 1 January 2019, a discard ban [Article 15 of EC 1380/2013, the so-called “landing obligation” (LO)] obliges fishers of all fleets to reduce discarding and follow specific management guidelines for catches of species which are subject to minimum conservation reference sizes, as defined in Annex III to Regulation (EC) No. 1967/2006 in the Mediterranean, and to total catch limits generally in Atlantic fisheries. All catches of regulated species must be hauled and retained on board, recorded and landed. The discard bans that have been implemented have not shown positive impacts in all the fisheries in which they have been applied (Condie et al. 2014). Several consequences may arise in European fisheries, including shifts in the ecosystem functioning and alterations to the socioeconomic status of the fishing communities (Guillen et al. 2018).

The Mediterranean area is subject to intense fishing pressure, as 22 countries are fishing in its waters and exploiting the same fishery resources. Mediterranean stocks are at risk from overexploitation, with undersized individuals being under immense pressure (Tsikliras et al. 2015, Vasilakopoulos et al. 2014). Mediterranean discard rates are estimated to range between 13% and 27% (Tsagarakis et al. 2014), but discarding has increased over the last 70 years due to regulatory limitations and changes in market habits that have brought a drop in the commercial value of some species (Damalas et al. 2015). The reasoning behind discarding practices depends on many local parameters that differentiate the composition of catches and landings (Maynou et al. 2018), such as the socioeconomic profile of a fisher and its vessel, which may define the discarding practice followed (Christou et al. 2017).

Having regard to Regulation (EU) No. 1380/2013 of the European Parliament and of the Council of 11 December 2013 on the CFP, the European Commission enacted EU Regulation 2017/86 of 20 October 2016, establishing a discard plan for certain demersal fisheries in the Mediterranean Sea. Under Article 4 of the regulation, a de minimis exemption was set for quantities of species which define the fisheries. Discard plans were first introduced for species which define the fisheries in the southeastern Mediterranean [hake (Merluccius merluccius), red mullet (Mullus barbatus) and deep-water rose shrimp (Parapenaeus longirostris)]. These were in force between 2017-2018, when the total landings per vessel in 2014 and 2015 consisted of more than 25% of these species separately or in combination. On 1 January 2019, the European Commission introduced EU Regulation 2018/2036 of 18 October 2018, amending the Delegated Regulation EU 2017/86. Discard management plans are currently applicable to certain demersal fisheries in the southeastern Mediterranean Sea until 31 December 2019, following joint recommendations submitted to the Commission in 2018 by Member States that have a direct management interest in the area (Greece, Cyprus and Malta). The Commission suggests that Member States should commit to increasing the selectivity of the fishing gears to minimize unwanted catches in accordance with the results of current research programmes.

These three species are subject to the LO and constitute the largest catch fraction in terms of volume (Fig. 1), defining the demersal trawl production. These species are closely monitored through the existing national management plans and are subject to stock assessments by the European Commission Scientific, Technical and Economic Committee for Fisheries (STECF) and the General Fisheries Commission for the Mediterranean (GFCM). Information on the stock status of all three species can be found in the Greek Management Plan (2014) with data from 2009, while for hake and red mullet assessments for the Aegean Sea stocks carried out by the GFCM (2017) have shown that red mullet is in healthy condition and is exploited sustainably, but hake is overfished and the fishing mortality rate (F) is far above MSY levels. The problem of overfishing encountered in the Aegean Sea is closely related to growth overfishing due to the poor selectivity of fishing gears, as elsewhere in the Mediterranean Sea, where a large fraction of the catches of the target species are below their minimum landing size (MLS) and length at first maturity (Tsikliras and Stergiou 2013, Mytilineou et al. 2018).

More than 30 ecological-economic marine fisheries models have been formulated so far to evaluate the multidisciplinary impacts of prospective management measures and to contribute to effective decision making (Nielsen et al. 2017). For the Mediterranean Sea there is an extensive literature on bioeconomic modelling (Guillen et al. 2012, Rossetto et al. 2015, Maynou 2014), while for the Greek fisheries there are a limited number of studies on the demersal fisheries of the Aegean Sea (Merino et al. 2007, Maravelias et al. 2014, Tserpes et al. 2016) and on small pelagic species (Maravelias et al. 2014, Politikos et al. 2012, 2013).

The present case study refers to the Aegean Sea fisheries that exploit demersal stocks. Table 1 presents the discard rates at fleet and gear level for 2014. The approach followed herein analyses the possible supporting measures (legal, technical, market-based or effort-based) that can be applied in order to facilitate the rebuilding of demersal stocks and provide forecasts on the economic viability of the fishing industry for the next 20 years using a bioeconomic simulation model (Mediterranean FIsheries Simulation TOol-MEFISTO, Maynou et al. 2017). Here we study the possible socioeconomic and biological effects of alternative management measures in order to propose sustainable solutions for the fishery and resolve any issues that may arise due to the implementation of the new regime.

Under the status quo, the viability of the fishing industry in the Aegean Sea is threatened. According to our simulations, given the current management conditions, the three target stocks should generate a small increase in income in the long term. Nevertheless, in the last few decades the fleet has decreased to a great extent (Fig. 2), key stocks are overexploited, and the fishery is not considered sustainable, like other Mediterranean fisheries that are under an “alarming decline” (Froese et al. 2018, Vasilakopoulos et al. 2014). Projections under the baseline scenario have shown that SSB of hake is the only one that demonstrates a steadily decreasing trend. Hake is the most vulnerable species, according to the GFCM assessment (GFCM 2017). The stock is currently overexploited (Biomasscurrent/BMSY is 0.85) and overfished (Fcurrent/ FMSY is 1.17). The same assessment for red mullet indicates that the stock is in healthy condition, as biomass is above MSY levels and fishing mortality is below the FMSY (GFCM 2017). Exploitation patterns need to change if all stocks are to be fully utilized at sustainable levels and the profitability of the Greek fleets is to be secured.

In general, the trawl fleet records higher income per vessel but coastal vessels are numerically larger and thus contribute more to the economy of Greece in terms of both GVA and employment. Moreover, our results show that, when implemented in isolation, the discard ban will generate few economic incentives for fishers to operate more selectively. In our simulation, the lack of endogenous effort adaptation or a constant catchability assumption mean that any earnings or losses from the former discards brought to land do not enter the economy. Given the volumes of discards estimated for the target species of the Aegean demersal fishery, the economic impacts are expected to be low and will not incentivize major operational changes. Therefore, the discard ban in isolation will not result in stock rebuilding or improvement of the socioeconomic state of fisheries, but rather to a decrease in landings and long-term economic losses. The sale of former discards will bring small additional profits but will not compensate losses due to the landing of target species or sorting and handling costs (a “crash landing” obligation). Sola and Maynou (2018) produced similar figures but the Spanish fleet was shown to bounce back in the long term despite the significant losses of revenue in the short term. In fact, anything beyond the short to medium term depends on the initial conditions introduced in the model (e.g. uncertainty in the SSB/R relationship, internal investment, capital depreciation, discount rate and original F/FMSY ratio for each species).

Additional management measures should be considered in order to ensure a smooth implementation of the CFP. The current study has visualized the output of eight possible scenarios in order to enable comparisons of management strategies. The fishing mortality will not decrease until technical measures are applied in different forms, such as effort reduction and selectivity improvement, with the latter offering a greater benefit to stocks. The projections agree with those of Tserpes et al. (2016), who also pointed out the importance of decreasing effort in the Aegean fleet for stock rebuilding. Subsidies may result in higher profits for the trawl fleet, but their effect is highly controversial because they provide incentives for overcapitalizing the fleet (Sumaila et al. 2010). GVA was exceptionally high in the selectivity scenario (scenario 4) for protecting juvenile hake. By protecting the nurseries of target species and decreasing the fishing mortality at safe biological limits, this could result in sustainable production patterns. Measures to support the fishing communities need to be implemented to support the sector, which already faces serious problems due to the ongoing national economic recession and the ageing population.

Recent policy imperatives have focused on resolving sustainability issues, in particular on eliminating or reducing discards caused by fisheries harvest patterns and poor selectivity of fishing gears. By implementing a discard ban in mixed fisheries, evidence has shown that it is essential to examine the conditions under which discards are generated in order for them to be decreased (Condie et al. 2014). These policy imperatives can be put into practice thanks to the provision of solid scientific advice. Mixed fisheries management is now focused on simultaneously meeting conservation targets for multiple species and fleets by understanding the dynamics of individual fishers and fleets (Tidd et al. 2012). Implementing any management measure in multi-species fisheries is a difficult task (Alzorriz et al. 2018). European mixed fisheries are called to manage challenging situations: to enforce the minimization of undersized individuals for Mediterranean fisheries and to avoid losing opportunities in exploiting other species because of the lack of quota availability for certain (choke) species, a complex phenomenon that could arise frequently for Atlantic fisheries under the LO (Sánchez-Lizaso et al. 2018, Spedicato et al. 2018). The ecosystem approach to fisheries management can lead to effectively managed fishing activities. The new policy could improve the current state of fisheries resources in Greece by encouraging avoidance of unwanted catches, but only when combined with other technical measures. The results of this study show that it will be challenging, but not impossible under F reduction actions (as seen in Maynou 2014), to meet the CFP objectives regarding stock sustainability, i.e. to achieve maximum sustainable yield by 2020 for all stocks.

The market and regulatory constraints are the main reasons for discarding in Hellenic waters, but other reasons are also detrimental, including the low commercial value of the landings, fishing practices, mishandling on board, etc. (Tzanatos et al. 2007, Gonçalves et al. 2007, Christou et al. 2017). Therefore, under the LO, supporting measures should be established to discourage the marketing of undersized fish, monitor the fish supply and distribution chain by fostering traceability of fisheries resources from vessels to consumers, and increase stakeholders’ awareness through education seminars (Maynou et al. 2018). In general, the multispecific nature of Mediterranean demersal fisheries makes it difficult to reduce discards as policies are difficult to implement when there is a lack of clear métiers and high spatiotemporal variation in discard composition (Maina et al. 2018). Other studies have shown that if effort or quota restrictions are combined with a discard ban, this will result in additional costs and a short-term fall in income but will generate economic incentives to avoid unwanted catches (Condie et al. 2013). When a discard ban was implemented in a mixed fishery in the eastern English Channel, fishers’ behaviour changed to fully utilizing the cod quota or reallocating effort to areas and weeks in which cod catch was low (Batsleer et al. 2013). The CFP could create incentives to improve the harvest patterns (Prellezo et al. 2016) by enabling exemptions specific to each fishery and providing a regionalization of advice. Also, gear modifications could improve selectivity and enhance sustainability (Sola and Maynou 2018) and spatiotemporal closures could assist the rebuilding of fisheries through an increase in the SSB of targeted stocks (Russo et al. 2017). Measures proposed for solving the discards problem in Europe vary in form and application status (Sigurðardóttir et al. 2015). By improving the gear selectivity, the unwanted catches generated will be reduced at the point where they are generated, resulting in the impoverishment of the illegal market of undersized individuals.

Significant data issues arose in the writing of this manuscript because the implementation of the Greek National Fisheries Data Collection Programme has faced some difficulties in the last ten years (“data poor mixed fishery” Sgardeli et al. 2019). Things that were not taken into account in our analysis are the additional handling and disposal costs of former discards brought to land and any investments that the fishers must leverage in order to comply, but these are expected to be low (Maynou et al. 2018). Moreover, when a nursery closure is simulated, the length frequency data used to generate L₅₀ and L_to95 estimates for the target species derived were not spatially explicit. Another aspect that could be investigated is a selectivity scenario using the mesh panels or grids that have been successfully applied elsewhere. Mytilineou et al. (2018) completed research on the selectivity of trawl fisheries in the Aegean Sea using different codend mesh sizes under a national research program, showing the importance of the 40 mm square and 50 mm diamond mesh currently used by the Greek fleet in comparison with the previous gear (40 mm diamond), which had fewer escapees and more discards, but none of them achieved a value of L₅₀ close to the MLS. The willingness to pay scenario was based on a survey held in two other European countries, Spain and Italy (Onofri et al. 2018), where consumers assessed the value of the reserve price for a more sustainable fishery, but the consumption patterns and consumer choices may be very different for the Greek case. In fact, in Greece and in other Mediterranean countries, there is a strong local black market for undersized fish (Damalas and Vassilopoulou 2013) and for this reason discards appear to be low. Short-term incentives are important for increasing compliance (Pascoe 1997) and ensuring the implementation of the LO. Compliance levels among fisheries are highly uncertain and variable among areas in Europe (de Vos et al. 2016, Guillen et al. 2018).

To overcome the discard problem, a participatory approach needs to be followed to connect all available evidence (Maravelias et al. 2018). Given the peculiarities of European fisheries, appropriate management action is important to address any issues at local levels (Spedicato et al. 2018). The active involvement of stakeholders could increase legitimacy and reveal the main reasons for discarding in order to find relevant and effective solutions at local levels. Future work could be aimed at testing different mechanisms and incentives for increasing compliance towards a smooth implementation of the CFP. To this end, the managers should carefully examine all available ways to support the rebuilding of stocks and the adaptation of fisheries-dependent communities under the new regime by encouraging the adoption of more selective gears and techniques through the funding opportunities offered by the European Maritime and Fisheries Fund. It is still critical to resolve data deficiencies and investigate the potential consequences of supplementary measures introduced under the CFP. An improved application of fisheries management will be enabled through an evidence-based and adaptive policy.