The project STELLA (Gillnet-Solution-Approaches) aimed at finding finding solutions for the mitigation of unwanted by-catches of sea birds and marine mammals, and thus reconcile nature conservation interests and the interests of coastal fisheries in the Baltic Sea. The project was carried out by the Thünen Institute of Baltic Sea Fisheries (OF) from November 2016 to January 2020, funded by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety in cooperation with the Federal Agency for Nature Conservation. From February to July 2020, pending work was continued with funds of the Thünen Institute. The objectives of the project were executed in five work packages (WP): WP1 aimed to improve data collection from the gillnet fishery; WP 2 focused on technical modifications of gillnets to reduce unwanted bycatches; WP3 addressed improvements to two alternatives to the gillnet, the fish trap and the pontoon trap; the social-science WP4 dealt with the fishing practice in relation to the avoidance of undesirable by-catches. Finally, WP5 synthesised the results of WPs 1 to 4 and derived recommendations to policy makers. WP1 analyzed the structure of the German small-scale gillnet fleet in the Baltic Sea and was able to identify eight distinct groups, similar in terms of activity and fishing pattern, that were stable over time. The identification of these fishing groups is essential in order to find tailored solutions, because there can be no uniform approach to the transformation of the gillnet fleet given its heterogeneity. In addition, means of data collection have been improved in this WP. In particular, reliable, high-resolution effort data that have not yet been reliably available from this fishing segment can now be collected on vessels of all sizes using the smartphone application “Mofi” (“mobile fisheries log”) developed in the project. A test lasting several months in the commercial fishery was successful. The "Mofi-App" is continuously developed further to allow for e.g. the photographic documentation of unwanted bycatch or gear damage caused by grey seals in the area, aiming at making its use more attractive for fishers. After a thorough review of the state of knowledge at the beginning of the project, WP2 focused on improving the acoustic "visibility" of gillnets. In order to prevent harbor porpoises from entangling and drowning in gill nets, acrylic beads were identified as the smallest possible neutrally buoyant bodies, which appear like much larger objects for the acoustically-oriented harbor porpoise due to a resonance frequency. These beads, which were glued into the meshes of the gill nets, could make the net acoustically perceivable (“visible”) for porpoises. In order to test the effectiveness of this net modification, the “beads net” was tested in a commercial fishery which is known for elevated bycatch rates of porpoises (gillnet fishery for turbot in the Black Sea). The experiments showed evidence of a reduction in by-catches, but statistically significant evidence is still pending due to the overall low by-catch rates during the experiment. WP3, the second technical WP, advanced fish traps and a pontoon trap as an alternative to gill nets. Fish traps and pontoon traps are known to reduce the bycatch of seabirds and marine mammals considerably, but so far have a lower catchability for the target species; they are also more complex to handle than gill nets and are therefore rarely used in German Baltic Sea fisheries. It has been possible to increase the catchability of the fish traps and to adapt the pontoon trap to the special conditions in the German Baltic fisheries (e.g. use in exposed shallow-water areas, adaptation to the target-species spectrum). The increase in the number of grey seals in German Baltic waters and the increasing catch losses and damage to gill nets caused by this species will make the use of alternative fishing gear - such as fish traps - necessary in the near future. This could protect both the fishermen's catch from damage by the seals and the grey seals from drowning in the fishing gear. WP4 took the approach of using social science to develop adapted bycatch management. Research on fisheries management has called for years for consideration of people in the development of management tools, since successful management is based on behavioral responses of fishermen to imposed measures. Three types of fishermen and two different attitudes toward bycatch were categorised within the German Baltic small-scale gillnet fishery. An expert workshop identified potential management approaches that could avoid bycatch. Summary 5 These results were analysed in light of the types of fishers and their attitudes toward bycatch, and conclusions were drawn about which types of fishers could be targeted best with which management tools to promote their compliance. At the same time, changing fisher's attitudes toward bycatch events to understand the significance for a sustainable fishing was identified as one of the key actions. To date, a discourse has prevailed among fishers that describes seabird bycatch largely as a part of daily routine. Significant progress in transforming fisheries to reduce environmental impacts requires a change in discourse, fostered, for example, through co-management processes. In a number of important areas of work, STELLA was able to lay the foundation for the mitigation of by-catches of seabirds and marine mammals by gillnet fishing in the western Baltic Sea. Most of the work will be continued seamlessly, including in the context of follow-up projects, so that it could be implemented in fisheries in the foreseeable future. Gaps in knowledge exist mainly in aspects that are necessary to avoid seabird by-catches. These could not be addressed within STELLA, mainly because basic knowledge on sea bird behaviour is lacking. Such insights are a prerequisite for a systematic development of technical bycatch mitigation. The project results demonstrate that effort data can be recorded area-wide and in high resolution even on smallest fishing vessels, simple and cost-efficient using the smarthphone application “Mofi” developed within the Stella project. We therefore recommend to implement the required incentives or regulations to ensure a rapid start of such a data collection. With some time lag, needed for an unaltered determination of initial effort, by-catch data for endangered, threatened and protected (ETP) species should be systematically recorded and verified with the help of electronic monitoring systems. For their rapid uptake in the fishery, incentives should be created that can be specific to the needs of the identified fishing groups; quota additions and excemptions from closed areas appear to be a stronger incentive than monetary aids. For the individual identified fishing groups, tailor-made solutions should be developed, which on the one hand can ensure economically viable German inshore fisheries, and on the other hand reduce their environmental impact. This requires the timely development of an overall strategy. If available, technical solutions for fishing gear that are already in use can probably be introduced relatively quickly and with little conflict because they require little change in fisher’s behaviour. Depending on the solution, a mandatory introduction (like in case of the “beads net”) or a voluntary introduction with incentives (in case of alternative fishing techniques) should be provided. If technical solutions are (presently) not available, legal actions for the mitigation are required. Social-science aspects should be included from the very beginning when designing and implementing measures to reduce the environmental impact of fishing; and full involvement of all actors should be ensured for each measure (comanagement). The creation of incentives carefully tailored to the specific target groups identified in this project is necessary because of the great heterogeneity of German gillnet fleet. This will help to convey that the measures are also in the interest of the fishery.