Visual and acoustic effects of ambient noise on harbor porpoise in the Possession Sound

Harbor porpoise (Phocoena phocoena) are one of the most frequently sighted cetaceans in the Salish Sea and are referred to as a sentinel species due to their sensitivity to anthropogenic threats, including that of vessel traffic and boat noise. The abundance and frequency of harbor porpoise in the Possession Sound was examined using data collected by Ocean Research College Academy (ORCA) from late 2011 through early 2018. Both ambient noise and vessel traffic noise were monitored to see how different sound levels in aquatic ecosystems affect harbor porpoise visual and acoustic behavior. Since harbor porpoise are typically a shy, enigmatic species, a hydrophone was deployed on select cruises to capture harbor porpoise acoustics even if they were not visibly spotted. Additionally, when harbor porpoises were spotted, a hydrophone was deployed to capture the vessel and ambient sounds in the water as well as the acoustic behavior of the harbor porpoises. While humans have a hearing range of between 20 hertz to 20 kilohertz, harbor porpoise hear at a frequency between 100 hertz and 150 kilohertz. Using Raven Pro 1.5, the hydrophone recordings were examined for high frequency ambient noise and sounds from harbor porpoises. The visual and acoustic behavior of harbor porpoises was than compared between different levels of ambient noise to see if higher or lower noise negatively affect harbor porpoise in the Possession Sound.