Recent research has shown that the presence of commercial and tourist vessels negatively affects the feeding and social behaviors of harbour porpoises in coastal areas. An international research team led by Dr. Rachel Lennon from the University of Exeter analyzed recordings from an underwater acoustic monitoring system installed in the Little Belt strait in southern Denmark. They discovered that during the busy summer months, the continuous vocalizations of the porpoises decreased by up to 45% when vessels were nearby. The study highlights that harbour porpoises use specific vocalizations to hunt and communicate, and the presence of nearby vessels caused them to halt these behaviors altogether.

The Little Belt strait, known for its fast currents and heavy vessel traffic, is one of three straits connecting the North Sea to the Baltic Sea. To determine the impact of vessel traffic on porpoises, the researchers utilized data collected from underwater acoustic sensors installed by Aarhus University in Denmark and a UK-based marine acoustics company from October 2018 to December 2021. Their analysis indicated that the porpoises were more vocal and active at night than during the day, with the highest vocalization frequencies observed during the summer months. Yet, the significant overlap of their activity areas with vessel traffic mainly occurred during daylight hours, highlighting a concerning trend where the porpoises actively reduced their vocalizations by 45% during daylight when vessels were present.

The study raises implications regarding the health and population dynamics of harbour porpoises, which have high metabolic rates and require constant feeding. Disruption caused by vessel noise could lead to adverse health effects and a decline in their numbers. The findings were published in the journal 'Marine Mammal Science' and emphasize the need for better management of vessel traffic in sensitive marine areas to protect these marine mammals from ongoing disturbances.