MetaData from both research trips

The effects of pelagic trawling on the health and welfare of Atlantic herring (<i>Clupea harengus</i>) were investigated on a refrigerated seawater vessel operating in the North Sea. A total of 495 Atlantic herring (<i>Clupea harengus L.</i>)<i> </i>were sampled during five hauls from two fishing trips in September 2021 and 2022. For assessments of consciousness and mortality, a Reflex Action Mortality Predictor test (<i>i.e</i>. RAMP-test) was used on herring collected following trawling and pumping. Inspections for external and internal damage or injuries were performed via morphological welfare indicators and analyses of photos and radiographs. In addition, blood samples were taken and analysed for haematological indicators of stress. Following trawling and pumping, only 5% of the investigated herring showed signs of external injuries, and no internal damage was observed in the radiographic inspections. However, 96% of the assessed herring scored 0 on all three reflexes included in the RAMP-test, and were therefore judged as dead. On average, herring lost 95% of their scales, while 95% of herring had a very high degree of ruptured red blood cells (<i>i.e.</i> hemolysis). Extensive scale loss results in a deterioration of the skin's protective barrier function, which in turn impairs the osmoregulatory capacity of the herring. This was evident by elevated levels of plasma osmolality and circulating chloride concentrations, which could also likely explain the high occurrence of hemolysis in captured herring. Trawling time and catch size proved to be two important factors to consider, leading to increased plasma levels of osmolality and lactate and cortisol, respectively. In conclusion, the high mortality appears to be influenced by a combination of factors such as severe stress, loss of osmoregulatory ability, crowding density within the trawl, and extended trawling times. This study provides important information on the welfare of wild Atlantic herring caught using pelagic trawls and highlights areas where improvements can be made to safeguard the welfare of fish captured in pelagic fisheries in the future.