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Acoustic deterrent devices (pingers) that are designed to alert marine mammals to the presence of fishing gear have been successfully employed to reduce cetacean–fishery interactions. However, pinger sounds may affect fisheries target species: noise can induce short-term stress responses in fish that are reflected in increased blood cortisol concentrations and behavioural alterations, which may ultimately result in reduced catch rates. In order to test this hypothesis, the present study analyses the hormonal and behavioural stress response of European sardine (Sardina pilchardus) to a commercially available pinger—the 70 kHz dolphin pinger. The responses of wild captive fish to the pinger sounds were tested in tank experiments, measuring the stress level of fish by analysing blood plasma cortisol concentration and swimming behaviour. Mixed effect models were used for statistical analysis. During the experiments, pinger sounds caused subtle, but significant elevations in sardine plasma cortisol concentration and fish school compaction. However, when compared to the rates of increase reported for acute stress responses in similar studies, the observed increment was very small. This suggests that the sounds of the trialled pinger are not likely to significantly alter sardine behaviour and should consequently not have any negative impact on sardine catch rates.