Harbour porpoises are the most common cetacean in UK waters but are sensitive to noise and vessel disturbance. Boat traffic near feeding and resting areas causes welfare-relevant disturbance that may affect long-term population health.
Porpoises repeatedly displaced from productive feeding areas by vessel traffic must expand their search range, increasing energy expenditure at a time when they may already be in energy deficit. Noise masking prevents effective prey detection, reducing catch rate. Mothers with calves are particularly vulnerable as calves depend on frequent nursing and close maternal contact that is disrupted by flight responses. Underwater noise pollution from motorised vessels is invisible to observers but causes measurable behavioural and physiological stress in porpoises.