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Finding Fish Hotspots and Mapping Coral Reefs

Making Waves: Episode 130

Tim Battista viewing ROV dive screen

Exploring the Unknown

Join us for our interview with oceanographer Tim Battista (foreground) about mapping coral reef habitats in the U.S. Caribbean. He is shown here on April 1 viewing a live video feed from a remotely operated vehicle. This is the 12th consecutive year of an effort to map this region's sprawling coral reef ecosystem, home to an amazing variety of ocean life. In this photo, Remotely Operated Vehicle technician Jason White, University of North Carolina Wilmington Undersea Vehicles Program, can be seen in the background driving the ROV.


HOST: The ocean covers more than 70 percent of the planet's surface. It drives our weather. Regulates temperature. It's home to countless species. Yet we know more about the surface of the moon than we do the ocean floor.

Today we're going to hear from oceanographer Tim Battista, a NOAA scientist who is working to change that. Tim is going to dial us in on one important part of the ocean — the Caribbean. In late April and early March of 2015, he is co-leading a weeklong expedition on the NOAA Ship Nancy Foster to map out parts of a vast, sprawling coral reef ecosystem around the U.S. Virgin Islands — an undersea realm that we know surprisingly little about.

Tim, welcome to the podcast. So this is your team's 12th consecutive year of creating intricate three-dimensional maps in this region that show what lies beneath the waves. Let's start there. Why the Caribbean?

TIM BATTISTA: "There are fundamental data gaps in the U.S. Caribbean. And the U.S. Caribbean being one of the important coral reef ecosystems in the U.S., and so fundamentally we are conducting this mission to help fill those data and informational gaps and provide products that help researchers and resource managers be able to better perform their jobs, whether it's science or decision-making."

HOST: So could you talk about what you mean when you say 'fundamental data gaps?' What kind of gaps are you trying to fill?

TIM BATTISTA: "So what the NOAA ship presents is really a state-of-the-art capability to collect data both on the types and distribution of the bottom habitats — so the seafloor, coral reef ecosystems, as well as the distribution of fish throughout that space. So we're simultaneously collecting both the underlying habitats and the fish as they are associated with those habitats. We're basically pulling away the water. We can't see what's on the bottom from the surface, maybe we could go down and dive, as a diver, and see portions of it, but we're able to map huge areas in a relatively short amount of time in high detail. And we are figuratively taking the water off the surface and seeing what's down there: seeing the shape of the seafloor and seeing the composition of the seafloor, and seeing things that no one has really ever connected together. That's really intriguing to me. In some cases that reveals shipwrecks, other types of objects — we see a lot of military objects from previous days — but mostly just the uniqueness of the coral reef ecosystem."

HOST: And these underwater landscapes that you're mapping are places that we don't know much or anything about.

Tim Battista viewing ROV dive screen

Helping Hand

Tim Battista helps pull the remotely operated vehicle back onto the NOAA Ship Nancy Foster after an hour-long dive. During ROV dives, the vehicle explores the area with the aid of several video cameras.

TIM BATTISTA: "So much of the ocean has not been mapped and what has been mapped, even those areas that have been mapped, the data density is so sparse that you have a hard time really understanding what's down there. In many cases the places we go have not been visited for 20, 40, 50 or more years. To give you an example, last year we were mapping portions of Lang Bank on the East side of St. Croix and some of those areas had not been surveyed since the early 1900s and those were being done with what we would consider to be antiquated technologies. So a ship would go out and they would deploy what was called a lead line, which was essentially a string with a lead weight on the end of it, to measure the depth. Pretty good to give you a general representation of what's there, but they're maybe collecting 100-200 points a day, so they're missing a lot. You have a series of points and a lot of gaps between those points. And 200 points a day on a good day, let's say, back then and we're collecting 1500 points per day with our current capabilities. So I find that to be fascinating that we're able to provide a level of detail that has never been seen before."

HOST: What kind of tech are you using to get this level of detail? 

TIM BATTISTA: "So the NOAA ship has a variety of different acoustic sonars onboard and they serve different functions. And this is one of the amazing capabilities of the NOAA Ship Nancy Foster, is its breadth of capability. So the ship has two distinct multibeam sonars which in total represents three different frequencies of sound. Those frequencies allow us to map the seafloor at different depths. Typically, the higher the frequency of the sonar, the greater the data density, but higher frequencies are less able to penetrate deeper in the water. So if you're mapping in shallow waters you want a higher frequency; if you're mapping deeper waters you want a lower frequency. And the NOAA ship has, as I mentioned three frequencies and so essentially we're able to map about five meters water depth to 1,500 meters water depth. Quite a range. And what those sonars do is they project sound. And a multibeam is what they call a swatch system. So it is projecting sound is sort of a fan-like presentation from underneath the ship. That fan represents a collection of about 300 individual beams of sound. Those beams of sound are broadcasted out from the bottom of the ship and then it's listening for their return. And as the sound propagates, eventually it hits the seafloor and bounces back up. Through physics, we know that sound travels at relatively the same speed. So if we calculate the time from when it was broadcast to when it returns, you divide it by two (and you know the speed of sound), then you can figure out the depth. Sound speed does vary, so we have to correct for that. So if we could think of that sound broadcasting out, each ping is broadcast out about five times a second, and we have approximately 300 beams of sound. So 300 times five is about 1,500 soundings per second. And that density of data is what allows us to literally paint the seafloor. So we are painting the seafloor with sound and that information tells us the topography — which is a fancy word for the shape of the seafloor. So is that seafloor flat, does that seafloor have ridges, is that seafloor a shelf that's going from shallow to deep. Are there nooks and crannies? These are all properties that we want to know about. And that is topography."

HOST: So you paint the seafloor with sound to generate a picture of what it looks like. Can multibeam sonar tell us anything else beyond the seafloor's shape?

TIM BATTISTA: "The other aspect that comes from a multibeam sonar in addition to bathymetry and topography is what's known as backscatter. Backscatter is a term that describes the intensity of sound that is reflected from the seafloor. So I like to give an analogy when I'm talking to kids about singing in the shower. So when we sing in the shower, our voice sounds really good. You have a tile surrounding the shower, the sound is being broadcast through your mouth and reflects off that hard tile and most of it comes back to our ears and it sounds really strong and bright. And that's analogous to a hard-bottom feature on the seafloor. So if you had, say, a hard coral reef, a lot of the sound being broadcast from the ship is being bounced back and will be received. The other example, of course, is if we're singing in the closet. You have all those clothes hanging in the closet, right? Your sound is being absorbed by those clothes, they are absorbent material. Not all the sound is being returned to your ears. And it's the same principle with the seafloor. There are certain types of features that absorb sound such as mud. So we are able to look at the data from a sonar and using that principle I just described — sound intensity — actually map out the differences in the bottom habitat based on how much sound is being returned from the signal. So the combination of topography and the backscatter intensity allows us to create very detailed three-dimensional maps of the bottom. And we can bring that data into a 3D visualizer and drape the sound intensity over top of a model of the seafloor and look at it from all different angles to sea how the bottom changes over distances, and what types of habitats are on top of that seafloor."

HOST: That's really cool. So multibeam sonar is how you map the seafloor, but I understand that you use a different kind of sonar called a fish acoustic sonar to figure out exactly where populations of fish are located.

TIM BATTISTA: "These are scientific-grade sonar systems which measure things in the water column. So anything off the bottom and up to the ship. That can include small things like food or diatoms in the water, could be marine mammals, turtles, but mostly we're focusing on fish. It's a very good way of detecting fish in the water. And what's different than fish sonars you may have in your recreational fishing boat is that these sonars are able to accurately measure the length of the fish that it detects, and also very accurately capture where it is in space. So not only horizontally in space, but also vertically in space. Not all fish are distributed at the bottom, some may be higher in the water column, mid-column, or some may be near the surface. And both of these sonars work together, so we're running them at the same time. So not only are we mapping the seafloor and it's habitats, we're mapping the fish as they are distributed above that seafloor and we can start to make linkages on what types of fish are distributed over certain habitats, what size of fish are distributed over certain habitats, are they distributed differently day vs. night? Are they using different spaces at different times of the day? Are there aggregations present? If we find a high density of fish, a ball of fish if you will, at certain locations, then that suggests an aggregation, and these are all important things to bring together."

HOST: So you use the ships multibeam sonar and fish acoustic sonar for mapping the water column from surface to seafloor. But you'll also be bringing along a Remotely Operated Vehicle — a ROV — with a hi-def camera … and what are known as 'ocean gliders' to record underwater sounds. How will you be using these tools? Let's start with the ROV.

TIM BATTISTA: "We have the remotely operated vehicle which can go down and provide us the eyeballs underneath the water to see is the health of the ecosystem, are we dealing with live or dead coral, or helping us to understand what the sonars are capturing from the data they're collecting. The ROV allows us to take the data coming from the multibeam sonars and interpret it's meaning because that data may not be readily transferable to the human mind what it is. We know it's different, the signal may tell us it's different, but by putting the ROV down we can actually gets eyes on the bottom to see, ah, that signal coming from the sonar was mud, or that signal was a coral reef habitat. "

HOST: And the ocean gliders?

TIM BATTISTA: "So these are torpedo shaped vehicles which are autonomous, which means they act on their own, we program them to where they should be going. They go off on their mission collecting data without us having to interact with them at all and then they report out their findings, so that provides another capability without us even having to monitor them."

HOST: Speaking of the gliders, I want to ask you about one method that you'll be testing out to help you locate places where fish aggregate in this part of the Caribbean. If I understand this correctly, some species of fish gather to spawn in the spring timed with the lunar cycle and you'll be using the gliders to help you locate these spots.

TIM BATTISTA: "Some fish aggregate and many of those we're interested in are the fish that are economically and ecologically important. So for example, snappers and groupers. The ones that fisherman catch and we like to eat. Typically around the full moon, fish aggregate—they come from miles away, sometimes quite far, hundreds of miles—to generally one location and they aggregate together. It's basically synchronized spawning. So it's their reproductive strategy. So one of the interesting things during the aggregation is some species actually vocalize. For instance, some of the grouper species actually have a vocalization pattern, a grunting if you will, and that's considered part of their courtship behavior. One of the things we're exploring with the use of the gliders is being able to detect that vocalization. There are other researchers who are also looking at this. They put down hydrophones on the seafloor to listen for those vocalizations. Again, these aggregations are occurring generally in certain spots. If you put the hydrophone in the right spot, you might hear those fish eliciting that sound behavior. With the use of the glider, we're mounting a hydrophone on it, so it's listening. And the glider is swimming through the ocean, listening for those vocalizations. Our idea is we can't be everywhere at the same time, but the glider can maneuver itself along the shelf edge of the seafloor and listen for those fish. That could provide a very robust way for us to detect where aggregations are occurring that we weren't already aware of."

HOST: OK, so let's put it all together — from the gliders, to the ROV, to sonar, there a lot of different tools at play here. Why can't you just use the ship's sonar systems to create a map and call it a day?

TIM BATTISTA: "In doing science, we need to look at the environment at multiple spatial scales. The fine scale. So something as close as being able to see the nodules on a coral or the blades on a sea grass. And then looking out a little broader than that, we need to see how those features are in the context of the features around them. And then, beyond that, the broad scale. So how do those smaller things fit into the context of a much bigger picture. Say on the scale of a geologic feature, a promontory, or a ledge or something like that. So looking at all three scales not simultaneously but together helps us get a better picture of the landscape. Because all those factors are important in understanding perhaps where fish are going, why they're going there and how many are going there, as well as the distribution and health of the coral reef ecosystem. "

HOST: So how much time do you have to gather all of this data during one of these yearly expeditions? What's a typical workday like?

TIM BATTISTA: "This year in 2015, we have eight science days aboard the NOAA ship Nancy Foster. Our time on the ship is, of course, short but the ship operates 24 hours a day so we have time to conduct science both night and day. A typical workday is comprised of basically three components. We break them up into eight-hour shifts. So during the daytime, we're conducting remotely operated vehicle transects. We deploy the vehicle in the water. It's imaging the bottom, taking pictures and exploring transects — those are lines — along the seafloor. And then we transition into evening operations, which focus on collecting acoustic information. And so literally the ship is driving lines, mowing the lawn we call it, back and forth across the seafloor, and they're imaging the bottom with acoustic sonar. And that continues throughout the night. And then in the morning we wake up and basically do it all over again."

HOST: And here's one thing that's not quite clear to me: who is all this data for? How exactly will it be used?

TIM BATTISTA: "We are collecting data that could be used to serve a variety of needs simultaneously. One of those needs is for the Coral Reef Conservation Program of which I am being funded by. They are charged to conserve and manage coral reef ecosystems. One of the others is NOAA's Office of Coast Survey who are charged with producing navigational charts for safe navigation. So we collect data to a standard that can be included in updates to nautical charts. So the other area—we collect information on the distribution and abundance of fish with the fisheries sonar. We are now collaborating with NOAA's Fisheries Service to try and make possible means that they can utilize that data as part of their management measures, the federal management measures, for conserving and managing fish populations. That is still a work in progress, but we're collecting a lot of data that can help compliment their studies. Additionally, there are the resource management agencies other than NOAA's Coral Reef Conservation Program who are charged with making decisions about the protection or limits or other measures for the areas that they're responsible for. So this would be the U.S. Virgin Islands territorial government. So that data is very valuable to them for providing a time series of the condition of the ecosystem at that location."

HOST: We have time for one more question. So you just said that this data provides a time series of the condition of this coral reef ecosystem to help people basically understand what's going on beneath the waves. And in the U.S. Virgin Islands, of course, the ocean is a huge part of the livelihood of most people. What kinds insights might the data you collect provide?

TIM BATTISTA: "So in the case of the U.S. Caribbean, there are a number of known human stressors in that region. Whether it's development, nutrient runoff, sediment runoff, putting in fiber optic cables or other types of cabling, fishing pressure … so these are stressors that they are wrestling with how to balance their economic needs with conserving the ecological needs. Our activities fall in support, we hope, of many of the decisions they need to make regarding place-based conservation. So this information we think will readily support a resource manager or a decision-maker in determining how to best conserve, utilize, and balance those conflicting uses.

HOST: That was NOAA oceanographer Tim Battista with NOS's National Centers for Coastal Ocean Science. Thanks for listening to Making Waves from NOAA's National Ocean Service.