Reducing Shipping Noise for Fatter, Happier Marine Mammals

Human-made noise from shipping is an ongoing problem for aquatic life. However, actually implementing measures to reduce noise can be costly and time consuming-- a risk many ship makers don't want to take without knowing how effective those methods will be. In this episode, we talk with Vanessa M. ZoBell (Scripps Institution of Oceanography) about her research that simulates the impacts of various strategies, with hopes for finding the most effective methods to improve the lives of our underwater neighbors.

Associated papers:
- Vanessa M. ZoBell, John A. Hildebrand, and Kaitlin E. Frasier. "Assessing approaches for ship noise reduction within critical whale habitat." J. Acoust. Soc. Am. 156, 3534–3544 (2024). https://doi.org/10.1121/10.0034455

Read more from The Journal of the Acoustical Society of America (JASA).
Learn more about Acoustical Society of America Publications.

Music Credit: Min 2019 by minwbu from Pixabay. 

Transcript

Kat Setzer (00:06)

Welcome to Across Acoustics, the official podcast of the Acoustical Society of America's publications office. On this podcast, we will highlight research from our four publications. I'm your host, Kat Setzer, Editorial Associate for the ASA.

Kat Setzer (00:25)

In this podcast, we've spoken with a number of researchers about the impact human-made noise has on aquatic life. Today I'm speaking with a researcher about how we can actually reduce noise levels for marine mammals. With me is Vanessa ZoBell, who will be talking about her article, "Assessing approaches for ship noise reduction within critical whale habitat," which published in the November 2024 issue of JASA.

Thanks for taking the time to speak with me today, Vanessa. How are you?

Vanessa ZoBell (00:50)

I'm doing good, how about you?

Kat Setzer (00:53)

Pretty good. So, tell us a bit about your research background.

Vanessa ZoBell (00:56)

So I started acoustics research when I got an opportunity to actually study bird acoustics in Tahiti and that was very different from what I do now. Most of my research is in the ocean-- well, actually, all my research right now is in the ocean, but back then I was hiking around and putting bird recording devices in trees and stuff and listening to bird song. And then I realized that I wanted to study human and wildlife interactions. And one of the topics that was interesting to me was underwater noise and marine mammals. So I came to Scripps Institution of Oceanography and I got my PhD in the Scripps Whale Acoustics Lab with John Hildebrand where I studied how to reduce noise in habitats where marine mammals occupied a lot of their time and then also looked into different designs of ships and stuff that could also reduce noise. And now I'm a postdoctoral researcher in the Scripps Machine Listening Lab, still at Scripps, with Kaitlin Frasier.

Kat Setzer (02:04)

Awesome, very fun. So we know that underwater radiated noise from ships is a problem for aquatic life. How big of an impact does it have?

Vanessa ZoBell (02:11)

Yeah, it's interesting because it can really impact a variety of different animals, not just marine mammals, in a variety of different ways, depending on the species, depending on the sex, depending on the age. So I'll just give a few examples, underwater radiated noise from ships and other sources of anthropogenic noise, like air guns and seismic surveys and stuff, can reduce the communication range

And sound to these animals, especially marine mammals, it's their everything. It's how they perceive the world around them. It's how they find their food. It's how they find each other during long migrations. It's how they show displays during mating seasons. So it's really important they can hear each other and then that communication's not masked. But when there is anthropogenic noise or human-made noise, like ships in the water with them, it can mask their communication. It's also been seen to increase stress hormone levels within these animals. Just like humans, if you're stressed out and if your stress hormones are raised, it can really affect your health and it can affect you in other ways beyond just being stressed out. It can affect your sleep, which can affect your day-to-day activities as well.

And then it can also alter these animal's behavior. It can make them leave a region, which might not be good if the region that they're leaving is super high-quality foraging area. We want these animals to be eating a lot, to be fat, happy ,and healthy. And if they're ditching those areas because it's uninhabitable, then that is, it's not what you want to see. 

Kat Setzer (03:51)

Yeah, you want those fat, happy marine mammals.

Vanessa ZoBell (03:56)

Yes, for sure.

So what's currently being done to reduce underwater radiated noise?

Vanessa ZoBell (04:01)

So there's a lot of different techniques being explored right now, not just in Southern California where my research is, but all around the world, in Canada, on the East Coast as well. So there's operational methods like vessel speed reduction. We've seen that vessels reduce their speed, the underwater radiated noise is reduced as well. And you get about a one dB per one knot relationship. So if you slow down two knots, then you get about a two dB reduction in source level of these ships. So operational methods like that. You can also, people are looking at different designs—so different propeller designs, different bow designs. And I think included in designs, people are also looking into coatings that they're putting on the hulls of their vessels that can reduce underwater radiated noise. So a lot of different things coming out of design right now. And then another one would be, I guess it's kind of operational or maybe more strategic, but figuring out how to reduce the count of vessels in a region, which you can get at by queuing. So if a vessel's going from Northern California to Southern California, instead of the "hurry up and wait" approach, where they're zipping down the coast and just waiting outside because they got there early, they have the just-in-time approach where they say, "Hey, this is the time when you're going to come into the port. Go slow and no need to rush. You'll get there right on time." So they can go 10 knots down the coast and get there right in time instead of zipping down 20 knots and then waiting for a couple of days outside the port.

Kat Setzer (05:49)

Okay, okay, that makes a lot of sense. So amidst all these methods, you've classified some methods as "source-centric" or "space-centric." What did you mean by those terms and why did you use that terminology?

Vanessa ZoBell (06:00)

So I guess all the examples I gave so far were more source-centric approaches, where the source-centric approach is we are trying to reduce noise at the source of the noise-generating mechanism, which predominantly is propeller cavitation for these vessels. There's also vibrations from the hull and engine noise, but majority of the underwater radiated noise is from propeller cavitation.So vessel speed reduction reduces propeller cavitation. Some designs, like differences in propeller designs, differences in bow designs, that can affect the flow regime at the propellers. Those are all different methods or strategies to reduce noise at the source of the vessel. And even the queuing, if you're allowing vessels to slow down and do the just-in-time approach, they're slowing down and that's also reducing noise at the source. So those are kind of the source-centric options. 

The space-centric options, which I haven't touched on yet, which would be if you want to reduce noise in a certain region, that's maybe a critical habitat of an endangered whale, you might increase noise in a different region, like an oligotrophic gyre where there's less nutrients and less biodiversity, in order to reduce noise in a more critical habitat. So that's the space-centric option where how can we kind of strategize which regions or which spaces are experiencing that underwater radiate noise and can we reduce it in spaces are more critical for noise reduction.

Kat Setzer (07:45)

Okay, it's kind of like in the air, you don't want sonic booms over land where people live. So you move the sonic booms to other areas. It's kind of the same thing, but with underwater. 

Vanessa ZoBell (07:54)

Totally, yeah. Yeah, and yeah.

Kat Setzer (07:56)

Okay. Okay. So what are the challenges with the current methods for reducing vessel noise?

Vanessa ZoBell (07:59)

I think a lot of it is, you logistics and strategy and reaching all the stakeholders and parties and groups that are involved. In terms of shipping, the shipping industry has a lot of other priorities than reducing speed. They're trying to not get fined for being late at the port. So work with the people in logistics and work with people that make their schedules and knowing that these companies are making their schedules months in advance. So we can't really be telling them minutes before, "Hey, can you slow down now?" But working with them in programs which exists, vessel speed reduction programs where we can incentivize them and give them positive public recognition to incentivize them to slow down more. Just organization and strategy and logistics is the big one for getting these methods to work. And then also the design aspect. The engineering behind all these designs is super up and coming, like electric engines, hydrogen hybrid systems, making it efficient for these huge container ships to take on these new designs. And maybe that's sometimes starting small, starting with the smaller vessels like tugboats that are getting the electric engines and then building up the engineering side from there to be able to work with the larger vessels. Or I've seen even some design schemes showing kind of like a, showing like the Prius of the container ship, a hybrid system where you have like...

giant sails in addition to a diesel engine so you can kind of have a hybrid system. So there's so many designs and whether they work in reducing noise part of the equation too. So you can strap on all these bubble curtains, sails, and then having one of those ships pass an instrument and getting a measurement from them takes a lot of organization and then sometimes increases noise and we have to figure out why. So getting all those studies done and figuring out the most efficient ways to reduce noise is definitely a challenge.

Kat Setzer (10:23)

Right, right. So your work has focused on the Santa Barbara Channel. Why? Can you tell us a bit about this region?

Vanessa ZoBell (10:29)

I would love to. I love this region. I think it's so interesting because Santa Barbara Channel, for our listeners, is right in Southern California and it is the California current flows equatorward and it makes this beautiful upwelling across the California coast, which brings about an abundance of biodiversity. There's so much nutrients that we have many different marine mammal species off our coasts from dolphins to large whales to fish to seals and sea lions and so much is going on. In the Santa Barbara Channel, we also have the Channel Islands, which create even more boundaries for upwelling to occur and even more nutrients. So the endangered Northeastern Pacific blue whale comes to this region around the Channel Islands during their foraging season. And they are gulping up all of that good krill that really is, the Santa Barbara Channel is a really special place for that whole thing to happen. 

They did not know this when they were building the busiest shipping port in the Western hemisphere, the Port of Los Angeles. 

Kat Setzer (11:50)

Oh no!

Vanessa ZoBell (11:51)

Yeah. So we have the foraging region of an endangered whale right up next and intersected by the shipping lanes that transport cargo to and from the first and second busiest shipping ports in the Western hemisphere, Port of Los Angeles and Port of Long Beach. So we have a really big human-wildlife interaction in this region and to be able to communicate with the folks trying to protect this endangered whale and the folks at the Channel Islands National Marine Sanctuary in addition to the shipping industry partners and in addition to the partners at the port, it's, you know, there's a wide variety of stakeholders involved. And what I learned from doing my PhD in that region is just you really talk to the folks involved, they care and they want to reduce noise and they want to figure out a way that we can coexist and share that region in the most sustainable way. So I think that is a cool project.

Kat Setzer (12:59)

Yeah, very cool. Everybody wants to have fat, happy whales, apparently. So what was your goal for your study?

Vanessa ZoBell (13:08)

So the goal for this study was to look at this region in the Southern California area, the Santa Barbara Channel, and to really zero in on three critical habitats: the Channel Islands National Marine Sanctuary, which is protected under the National Marine Sanctuaries Act in the US, the humpback whale biologically important feeding area, and the  blue whale biologically important feeding area. And both of these animals are under the Marine Mammal Protection Act and the Endangered Species Act in the US. And so I wanted to, as I mentioned at the beginning of the podcast, so many different strategies that people are doing right now to reduce noise. And I wanted to model all of those different strategies to identify which strategy would be the most efficient in reducing noise in those three critical habitats. Some of these strategies are going into effect already, some haven't. So in order to figure out which strategies we should focus on and kind of try the hardest to get going, I wanted to simulate before because it can cost a lot of money in order to take on these initiatives and if they don't really reduce noise then we should know that before trying to do them.

Kat Setzer (14:35)

Right, right. That totally makes So what noise mitigation techniques did you look at, and how did you assess their effectiveness?

Vanessa ZoBell (14:44)

So I looked  at some source-centric options. The source-centric options I looked into speed reduction. First, I simulated if all of the ships in the region slowed down to 10 knots. I then just said, “OK, maybe not all the ships. Let's just slow down cargo ships, because at least in this region, it's about two-thirds cargo ships.” So just slowing down those giant big boats, maybe we could get a lot of bang for our buck by just trying that. The last source-centric option I did was I simulated if all these ships got a new design. So we studied a while ago that this some cargo ships, there was a in noise by three decibels. So I said, "Okay, let's just pretend that all the cargo ships got redesigned in that way, and see how that would affect the noise." So that's what we looked at for the source-centric. 

For the space-centric, I said, "Okay, here's where the ships are. Here's where the shipping lanes are right now. Let's say that they actually go on the southern side of the channel. So let's split them up a little bit. Okay, let's see if we change the shipping lane in this way." So I did a couple of different simulations where I put ships in different areas. I did one simulation where I just completely deleted the shipping. I deleted any ship going through the Santa Barbara Channel, any cargo ship going through the Santa Barbara Channel. I said, “Go south, go on the southern side of these fake made up shipping lanes that I just made up in my office. And let's see what that would sound like.” Obviously, as a scientist, you can model whatever you want. You can model the perfect world and it takes a lot of, you know, federal registry and policy making to actually get that into effect. 

Kat Setzer (16:25)

Right.

Vanessa ZoBell (16:34)

But we can kind of model what it would be like in a different world too. So those were the space-centric options that I looked into. So a little bit of both.

Kat Setzer (16:43)

Okay, okay.

Vanessa ZoBell (16:45)

And then to assess their effectiveness, I took the simulated model and I subtracted the sound levels in the simulated model from the original data, from what it was in reality during the month that I modeled from the real vessel locations and their speeds that they were going.

And then I saw, was there a reduction or was there an increase? I looked at the entire region and I looked at just the sound levels within those three critical habitats. And I saw that with the source-centric option, even though you're slowing a vessel down, which means it's in the area for longer, between the source-centric options, vessel speed reduction of all the vessels reduced noise the most in comparison to the design approach. But just slowing down the cargo vessels still was almost equal to slowing down all the vessels just because they are so big, so loud, and there are so many of them in that region. In terms of the space-centric options, there was some decreases in areas where we took out ships. And then, of course, there were some increases too. We put ships where they were not before so with that option you don't get a blanketed noise reduction result. You get reduction in areas the critical habitats, but then you get increases in regions are more offshore. And, of course I looked at three critical habitats. There are more that don't have delineated boundaries. So we have a lot of information on blue whales and humpback whales, but other species, like fin whales and beaked whales, they could also be included in this analysis in the future to figure out how to reduce noise in those habitats as well.

Kat Setzer (18:36)

You already sort of touched on this, but how do different noise mitigation techniques end up performing in your models?

Vanessa ZoBell (18:42)

So for the source-centric option, vessel speed reduction ended up performing in a way that reduced the most amount of noise terms of the source-centric options. For the space-centric options, moving the shipping lanes to the southern side of the island and creating a buffer between critical habitat boundaries and the shipping lanes allowed for the greatest noise reduction within those critical habitats. So as of now, there are no buffers required do whatever activities outside of the boundaries of a sanctuary or a biologically important feeding area. when you have a spreading threat, like noise pollution, I think that buffers are really important to consider because even though you're two kilometers outside of the boundary of a sanctuary, that noise is propagating a lot farther than that, so creating buffer areas for these spreading threats is an interesting and important topic to consider when thinking about where we're putting boundaries and if those boundaries need a little buffer the anthropogenic activity.

Kat Setzer (20:00)

Okay, okay, so to sort of jump off of that. How can your findings be used going forward to help inform protections?

Vanessa ZoBell (20:07)

Good question. I think that one thing that is pretty tried and true at this point is that vessel speed reduction is a good way to reduce noise. So I think that if… and a lot of ports are already incentivizing ships to go slow because in addition to reducing noise, it reduces greenhouse gas emissions too. And in these port cities, there's been history of lung disease and asthma for the citizens that live there. So reducing both pollution above water, GHG, and below water, noise pollution, is an amazing way to get the most bang for your buck. So vessel speed reduction in areas with critical whale habitats  and port cities is a really good method for reducing noise.

In addition to marine spatial planning is, I mean, it's a whole topic of study, but figuring out ways where we can put shipping lanes in a strategic area that dodge these critical habitats in the future is a really good way that we can mitigate ship noise in regions of concern. Redesigning shipping lanes if it's possible to dodge those areas or if new shipping lanes or fairways are being proposed, how can we best place them so that the ships, of course we need trade, so the ships can go where they need to go and then the animals can be protected as best as possible. So I think that marine spatial planning is a really important thing moving forward to help mitigate ship noise as well.

Kat Setzer (21:50)

Yeah, that does sound like a really interesting strategy. Do you have any other closing thoughts?

Vanessa ZoBell (21:54)

I think closing thoughts is that it is really interesting and a difficult but exciting field to be in the noise reduction field. just because I think that a lot of people care about this and I think that even our shipping industry partners really want to reduce noise and reduce GHG emissions. So figuring out how to work together in order to pull all this off is super important and bringing together the experts that can make decisions and best reduce noise in the ocean is super exciting and we need some creative and innovative approaches to make it all happen. So it's a cool space to be working in.

Kat Setzer (22:45)

Yeah, yeah. Exciting was the word I was thinking, too. It is exciting to think that your research could bring us one step closer to improving the acoustic environments for aquatic life. So thank you again for taking the time to speak with me today. And I wish you the best of luck in your future research.

Vanessa ZoBell (22:58)

Awesome, thanks for having me.

Kat Setzer (23:00)

Yeah, you're welcome.

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