A significant quantity of unexploded ordnance (UXO) lies on the North Sea seabed. Uncontrolled detonations of these wartime relics pose severe risk, including fatalities to both humans and marine life; consequently, their presence is a matter of grave concern, necessitating removal. This study is the first to examine impacts of high-order UXO detonations on the behavioral response of harbor porpoises based on in situ data.
Impacts were evaluated for four UXOs at the East Anglia ONE wind farm (southern North Sea) detonated without noise abatement. Impacts were most substantial for the heaviest UXO (1000 lb), where porpoise occurrence and presence of echolocation buzzes, indicative of potential foraging behavior, were substantially reduced after detonation compared to before out to a distance of 15–20 km. In contrast, increased porpoise detection and buzz rates were found beyond this distance when assessed over increasingly longer periods, suggesting displacement of individuals.
While impacts from detonations could not be disentangled from related detonation activities, e.g., vessel presence, acoustic deterrent device activation, and fish scaring charges detonation, results show that the overall high-order UXO detonation process can result in porpoise displacement and impact potential foraging activity. Further empirical research on behavior responses to UXO clearances is urgently needed.