Effects of fishing pressure on wild cod during spawning season

In recent years, commercial fishing has contributed to the depletion of marine fish stocks, with potential consequences not only for population abundance but also for reproductive performance and physiological condition. This study investigated the effects of fishing pressure on Atlantic cod (Gadus morhua) in northern Iceland by comparing individuals from areas exposed to high and low fishing pressure following seasonal closures. This thesis investigates the effects of fishery on individuals by evaluating gamete quality (including sperm motility and gamete cortisol) to assess reproductive success, alongside the impacts on three different brain regions (brain stem, telencephalon, and hypothalamus), focusing on the serotonergic and dopaminergic systems and plasma cortisol concentration. The most relevant results were a significant reduction in sperm motility and lower hypothalamic dopamine concentrations in fish from highly exploited areas, suggesting potential effects of fishing pressure on both male reproductive performance and neuroendocrine regulations, in contrast, plasma and sperm cortisol concentrations, together with serotonergic activity, showed no significant differences between fishing pressure regimes, providing no clear evidence of an acute stress response at the time of sampling. Overall, these findings suggest that fishing pressure may influence both reproductive performance and specific neuroendocrine pathway in wild Atlantic cod. The observed effects support the potential value of seasonal fishing closures as a management tool to reduce disturbance during spawning and contribute to stock resilience and long-term fisheries sustainability.