Fishing gears, and especially those that are towed across the seabed, can impose a number of impacts on the marine environment. The long term implications of many of these impacts are poorly understood and often hard to quantify from both the ecological and economic perspective (L0kkeborg, 2004). At a global level the general trend towards ecosystem based management (FAO, 2003; Pikitch et al .. 2004) and adopting the precautionary principal (FAO, 1995b, 1996) implies these impacts should be reduced. Within Europe, the focus of management has primarily been on reducing the level of commercially important species being caught incidentally ("bycatch") and subsequently discarded. These reductions have mainly been pursued through the application of restrictions on the type of fishing gear that can be used (generally termed "technical measures"). However, hard management constraints such as technical measures tend to impose increased costs on fishers, primarily through reduced productivity. These create incentives to mitigate the effectiveness of the measures, and may ultimately result in a failure to achieve the management objective. Despite ongoing attempts to reduce these impacts, bycatch and discarding rates are estimated to be in the range of 20% to 60% of catch weight for European fisheries (European Commission, 2007b). This study investigates the importance of individual environmental impacts within the context of European demersal trawl fisheries and then assesses the effects of attempting to reduce one of these impacts, that of bycatch and discarding, through the application of gear based technical measures. Priorities for the reduction of impacts are quantified at the stakeholder group level using the Analytic Hierarchy Process (AHP). The results indicate that Europe's historical focus on reducing primarily commercial discards with technical measures needs to be broadened to account for other non-commercial impacts. The effects of attempting to reduce bycatch and discarding through the application of gear based technical measures are then considered using two case studies. Ex post assessments are undertaken on two fisheries; the UK East coast Crangon crangon (Brown shrimp) fishery and the Belgian large beam trawl fishery. In both instances vessel level productivity was observed to have fallen as a result of taking up bycatch reduction measures with productivity effects estimated to range between -14% and -23%. On the basis of these findings, a review was undertaken of alternative measures that may better account for the set of incentives fishers face. Whilst not yet widely applied in the context of fisheries, their potential tb simultaneously improve both economic performance and resource sustainability means they have been receiving increasing attention (Grafton et al., 2006a). Such measures appear to provide a potential solution to the main issues surrounding command and control type measures and are likely to have application when attempting to reduce discards in fisheries.