Killer whales are mammals relying on sounds to collect information from the environment, communicate with other individuals, detect potential threats (i.e. predators or competitors) or search for food. Naval traffic is one of the main sources of underwater anthropogenic noise and has the ability to interfere with the sound reception of killer whales and other cetaceans, a phenomenon known as “auditory masking”. This study shows the pattern of killer whale vocalizations detected in co-occurrence events with naval traffic noise between January and June 2018 in Northern Norway. Median sound pressure levels ranged between 65.5 and 119 dB re 1 μPa2 across 1/3 octave bands (13 Hz – 16 kHz). The highest SPL levels were found at frequencies below 1 kHz and statistical analyses showed a connection between these values and the presence of vessels in the area. Analyses of killer whale acoustic detections confirmed interactions with fishing vessels, while the coupled effect of noise level and vessel proximity suggested the presence of the Lombard effect in the whales exposed to noise pollution. These results provide a finer-scale understanding of the effect of naval traffic on killer whales’ acoustic behaviour, taking into consideration also vessel types and dimensions, useful for improving targets in management strategies in areas where killer whales are often exposed to anthropogenic noise.
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