I was at school when I discovered cavitation. There was a prize up for grabs for a project on any science-based topic and I mentioned this during my round of university interviews. One of the academics I met suggested looking at propeller cavitation and provided a pile of papers and strobe-lit photos. I won the prize, which was a book of my choice: I selected one about sailing.
Both those interests have sustained my interest over the years and both came together this week at a 2.5-day workshop that focused on underwater noise. In fact, it was still going on when I started writing this item on Friday (1 February) so I don’t yet know its final outcomes, but I heard enough to know that propeller cavitation and machinery noise are wreaking havoc with many marine species.
The scale of the problem was made clear in an extract we were shown from a 2016 award-winning film, Sonic Sea, which looks at the problems caused to marine life by the increasing noise in the world’s oceans. I jotted down a few details from its narrative: “the noise environment in the oceans is doubling every 10 years”; “whales can’t turn the volume down”; and perhaps most importantly, “one of the things about noise in the water is that humans are not aware of it.”
That is why there has been little focus on this topic over the years. Ballast water bugs, toxic anti-fouling paint, exhaust emissions: The environmental impact of these is clear to see but, unless we regularly put our heads underwater, noise from ships does not catch our attention.
But it is increasingly becoming a concern and the full-length Sonic Sea, along with many other reports that can be found with a simple Google search, connect ship noise with the phenomenon of whales swimming onto beaches when they should be in deep water.
This week’s workshop is not the first to address the problem and an earlier item published by ShipInsight ahead of the event includes references to other work and described some Canadian initiatives to address the problem. But this latest gathering is probably the one that will have the greatest impact because it has tacit support from IMO.
It was organised by Transport Canada, which is a government department responsible for that country’s transport policy, but took place at IMO’s headquarters in London, at no cost to the organisers. Transport Canada’s director of clean water policy, Michelle Sanders, saw that support as significant. It is “an indication that there’s interest [at IMO] to explore this issue more,” although “what form that takes is to be determined,” she told ShipInsight.
Hiroyuki Yamada, director of IMO’s Marine Environment Division, delivered an opening address that catalogued the organisation’s work on this topic, going back to the early 1980s and culminating in its 2014 Guidelines for the Reduction of Underwater Noise from Commercial Shipping to Address Adverse Impacts on Marine Life in 2014 (MEPC.1/Circ.833, which can be found via IMO DOCS). But he acknowledged that those guidelines offer only “general advice on the matter”.
That was inevitable, he suggested, because of the “significant knowledge gaps” and the complexities of assessing the contributions of various noise sources to the problem. So he described this latest workshop as “essential to guide future discussions on underwater ship noise” and predicted that its outcomes “will prove vital to any future review of the guidelines.”
Chairing the workshop was Michael Bahtiarian, who had advised the US delegation when IMO’s 2014 guidelines were drafted. He is principal consultant at the US consultancy Acentech, which specialises in sound and acoustic engineering, and told ShipInsight that the event’s outcome could be recommendations for more research or it could be a call for action. “There is certainly an idea that something has to be done,” he said, “that IMO has to take up the matter a bit more seriously.”
Nathan Merchant described the impact of underwater noise on marine species. He is the principal scientist and team leader for the Noise and Bioacoustics Team at a UK government agency, the Centre for Environment, Fisheries and Aquaculture Science (CEFAS) and he pointed out to the workshop that the period of human impact on the marine soundscape has been very short compared with the evolution of animals that use sound to communicate, navigate and detect predators and prey.
It is not just whales and similar creatures that are affected: as many as 130 species have so far been identified as being affected by sound, some of which “have an important role in ecosystem functioning,” he said.
He displayed a diagram illustrating measurements that showed how some fish dived deeper as a ship approached to avoid its noise but he was asked during the discussion whether this might have been caused by the fish seeing, rather than hearing, the vessel. He said it was not: there were some sailing boats in the area when the measurements were being taken and they did not have any effect on the fish, he said.
I will be writing further about some of the other details covered during the workshop, in particular about the noise generated by machinery and transmitted directly into the sea through a ship’s structure. That and propeller cavitation are the two largest sources of underwater noise, the workshop heard.
IMO delegates will have an opportunity to review the workshop’s output at the next Marine Environment Protection Committee meeting (MEPC 74) in May, when an information paper based on the workshop will be circulated to delegates.
• Documents and presentations used during the workshop can viewed here.