Turning Down the Volume on Marine Noise Pollution
Often when we think of marine pollution we think of physical items like garbage, or of chemical runoff from factories or cities, or large incidents like oil spills. While those forms of pollution are obviously very threatening to animals in the marine environment and have been extensively studied, one form of pollution which has only recently gained a bit more recognition is that in the form of noise.
What is marine noise pollution?
Quite simply, marine noise pollution refers to sounds which are not natural to the marine environment made by anthropogenic (human) activities, which can interfere with the ability of marine animals to hear natural sounds in the ocean.
Using sound is more important for marine life than you may think. Sound propagation in sea water is greater than light propagation, meaning that light decreases in intensity faster and easier as it travels away from the source than sound does. Sound also travels incredibly well in sea water compared to air, covering about 1500 meters per second (15 end-to-end soccer fields) which is about 4-5 times faster than it travels in air (about 340m/s or 3 soccer fields). Furthermore, under the right conditions and without interruption or hindrance, sound can travel thousands of kilometres without the signal losing considerable energy. Considering the utility of using sound cues over visual cues in sea water, it’s of no surprise that many marine species, including our resident marine mammals, have evolved to use sound effectively for navigation, feeding, communication, and for perceiving the environment around them.
Why is it a problem?
Since sound is of critical importance for the normal behaviour and survival strategies of marine mammals, marine noise pollution is considered a serious threat. Noise produced by recreational and commercial vessels, drilling and mining operations, and other anthropogenic activity can cut down communication space for marine life. This means that they are unable to effectively communicate with mates, family, offspring, feeding groups, etc., and may also miss vital environmental cues like detecting a nearby predator, seeking food, or navigating to preferred habitats. This reduction in the ability to communicate has been shown to cause drops in population numbers, decreases in species diversity, damage to hearing organs, increases in stress levels, habitat displacement, and ultimately even death. Fortunately, with an increase in recent years of our awareness of the danger noise pollution poses to marine life, there has also been an increase in research and funding, with a focus on how we can reduce our impacts through policy and practice.
In fact, a study was published last year in 2021 which examined the differences in the marine soundscape of the Hauraki Gulf before, during, and after the 2020 COVID-19 lockdowns. This research found that through the enforced ban on recreational vessels during the lockdown periods, ambient sounds in usually busy channels dropped nearly 3-fold overnight, which increased dolphin and fish communication ranges increased by up to 65%. In sites near to Auckland City, communication ranges for dolphins increased by approximately 50 metres for every 10% decrease in vessel activity; in waters further out into the Hauraki Gulf Marine Park, ranges increased by over 500 metres. Information like this is vital to our understanding of how anthropogenic noise pollution changes the marine soundscape and affects the species with which we share the Hauraki Gulf, and ultimately will contribute to information policy-makers need to help us reduce the negative impacts we have.
Is there further research being done?
Auckland Whale and Dolphin Safari routinely collects acoustic recordings and other key data while out in the Dolphin Explorer and contributes this data to citizen science databases, research organisations, universities and government departments. In addition to this, University/Research Organisations often come onboard to use our eco-safari as a platform of opportunity to further the research of the soundscape of the Hauraki Gulf and cetacean communication behaviours, and ideally inform effective laws to regulate the impacts of anthropogenic noise on marine life.
Middel, H., & Verones, F. (2017). Making marine noise pollution impacts heard: the case of cetaceans in the North sea within life cycle impact assessment. Sustainability, 9(7), 1138.
Pine, M. K., Wilson, L., Jeffs, A. G., McWhinnie, L., Juanes, F., Scuderi, A., & Radford, C. A. (2021). A Gulf in lockdown: How an enforced ban on recreational vessels increased dolphin and fish communication ranges. Global Change Biology.
Putland, R. L., Merchant, N. D., Farcas, A., & Radford, C. A. (2018). Vessel noise cuts down communication space for vocalizing fish and marine mammals. Global change biology, 24(4), 1708-1721.