Trials conducted on board industry vessels to test gears or alternative fishing tactics are often adopted to test selectivity measures in the field. A challenge trial was conducted on board an Irish demersal vessel in 2015 to assess the potential of tactical and behavioural changes to reduce unwanted catches, in light of the introduction of the EU’s Landing Obligation. Initial analysis of the trial indicated that there had been limited success in avoiding choke species through tactical changes. Feedback from the skipper following the trial, however, indicated that every effort had been made to avoid unwanted catches. Consequently, trial results were further scrutinised to determine what behaviours had been adopted throughout the trial, how catch compositions related to reference vessels at this time and what the major drivers of catch patterns may be. Fishing behaviour and catches for the trial vessel were fairly consistent between both trial months. This was possibly as a result of avoidance behaviours being adopted throughout the whole trial. A comparison with reference vessels indicated that the trial vessel did catch lower proportions of haddock, a key choke, in relation to whiting, a non-choke species. Changes in depth fished and time of day fished could reduce the exposure to discarding haddock but not cod, another key choke. This study highlights the importance of understanding how observation and scientific collaboration with industry may influence fishing behaviour, and how scientists should carefully consider such factors when conducting trials on industry vessels and interpreting subsequent results.