Unveiling the biochemical and haematological profile of blue shark () in the Mediterranean after bycatch.

The blue shark () is the most frequently by-caught species in longline fisheries targeting swordfish in the Mediterranean Sea. The IUCN classifies the Mediterranean blue shark population as critically endangered, but no information on haematological or biochemical parameters is available for this population. Based on a multi-year dataset of 63 blue sharks () and 18 physiological parameters, this study provides the first detailed insights into the variability of physiological indicators following bycatch in the Mediterranean Sea. We also examined differences across three post-capture condition groups and assessed the potential influence of sex and life stage (juvenile vs. adult) on physiological variability. While no significant differences emerged between sexes or life stages, clear distinctions were observed between condition groups, particularly when compared to moribund or dead individuals (condition group 3). These sharks showed signs of enhanced physiological stress, including reduced glucose, elevated lactate, and altered osmoregulatory function (lower urea and chloride, higher phosphorus). These patterns align with stress responses previously described in other shark species. Overall, the study provides a valuable baseline for future research into the physiology and conservation of Mediterranean blue sharks' population.