Gray's Reef National Marine Sanctuary
Gray's Reef National Marine Sanctuary
2017 Gray's Reef Research Cruise Photos
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Gray's Reef Research
Expeditions 2017

Tuesday: June 13, 2017
Log Day 5

Aria Remondi
Gray's Reef Deputy Superintendent for Operations (Detail)
Savannah, GA

Today is a really exciting day for one of the projects on the NOAA Ship Nancy Foster, because it has begun in earnest! The network problem that I mentioned a few days ago significantly affected the work of Drs. Peter Auster and Fabio Campanella. They are studying predator prey interaction throughout the day in Gray's Reef. I spoke with them both about their work.

Dr. Peter Auster uses this 360 video camera to track behavior under water.

Dr. Peter Auster uses this 360 video camera to track behavior under water.
(Photo: Peter Auster, UCONN, Mystic Aquarium)

Aria: So what project are you doing, and what's the idea behind it?

Fabio: The idea is to use acoustics to characterize the distribution of predators and prey together with the scuba diving observations. Acoustics sees different things than scuba because the spatial scale is different. We are able to cover a lot of ground in a relatively small amount of time [with acoustics] and [the scuba divers] just have detailed point samples, but they see the actual predation events, see the species and all the interactions. With acoustics we get more data on fish size and distribution but it is still hard to get to the species level, so what we do is combine the information to ground truth the acoustic with the scuba diving.

The camera (on the right) takes video every 9 minutes for 2 days to study predator/prey interactions. Sometimes it catches sea turtles!.

The camera (on the right) takes video every 9 minutes for 2 days to study predator/prey interactions. Sometimes it catches sea turtles!
(Photo: Peter Auster, UCONN, Mystic Aquarium)

Aria: So what can you see with the acoustics? Can you see individual fish?

Fabio: We can see everything but it is hard to put specifics on what we are seeing, if it is a tomtate or a lionfish or whatever. What we can do is discriminate the sizes of the fish, and this is what we are doing now, trying to classify the species based on the size. It's not the size that you actually see; it's based on target strength which is a measure of the amount of backscatter. It depends on different things like the size of the fish, the morphology of the fish, if the fish has a swim bladder, and these kinds of things.

Aria: So the divers will use cameras, and also hydrophones for this?

Fabio: Yes, it's passive acoustics. It's a hydrophone that records all the sounds to characterize the soundscape.

A red snapper and a scamp grouper hunt a school of scad.

A red snapper and a scamp grouper hunt a school of scad.
(Photo: Peter Auster, UCONN, Mystic Aquarium)

Peter: What we are trying to identify [with the hydrophone] is if there are characteristic sounds of predation. One of the things that we want to ultimately understand is how a difference in the ecological resources in the area affects these interactions. We also look at how fish cooperate to hunt, just like lions on the savannah. Cooperating enhances their feeding rate and growth. How do these fish hunt in groups and how does that increase their food? So if there is a characteristic sound of predators eating, then we can get a better idea of the rates at which predation is successful without having to sit on the sea floor or catching fish and looking at their gut. Looking at their gut would tell us what they eat but not how they hunt. Basically, we are looking at the invisible life of fish predators.

Fabio: We are trying to cover 24 hours to see when the predation peak is. It is usually at the crepuscular period, so at dawn and dusk. The plan was to carry out six surveys every day at the same site [with an EK-60 echo-sounder which is a type of sonar]. So [surveying at] pre-dawn, post-dawn, during the day, pre-sunset, post-sunset and during the night. That way we are able to characterize the diel (24 hour) variability of predator prey distribution. In addition we will have stationary cameras deployed for 48 hours at some sites recording 80 seconds of video every nine minutes.

Aria: Does the camera see in all directions?

Fabio: No, but the field of view is pretty wide. The idea is to deploy two at the same site but at different part of the ledge. One where there is the highest level of prey and another at lowest activity level.

The EK-60 data is shown on the screens. The three large blue clusters on the bottom screen are likely tomtate schools close to the ocean floor.

The EK-60 data is shown on the screens. The three large blue clusters on the bottom screen are likely tomtate schools close to the ocean floor.
(Photo: Aria Remondi, NOAA)

Aria: What are you trying to understand from the predator/prey interaction? Once you have it what can you do with that information?

Fabio: The goal is to understand how distribution of predators and prey and predation activity are influenced by external factors such as habitat and hydrodynamics. This information is ecologically important because if you can actually understand the ecology of the species in this habitat, you can extend these to other areas. It's also important for management, especially in these past years that we are moving toward an ecosystem-based management. Predator/prey interactions are one of the processes that are very important to investigate in order to understand the dynamics of the whole system.

Aria: Is there anything we can change if you fully understood the interaction, whether you were trying to protect the predator or prey species?

Fabio: Hypothetically, yes but it is hard to translate all this information to actual management actions and it is one of the big challenges of ecosystem based management.

Peter: When not servicing the hardware [on a dive] we are looking at behaviors, specifically group hunting behavior of predators. We look at species, numbers, behaviors, and predatory attack and success rates. First off, this information enhances our basic understanding of marine ecology. On the management side, how important is one species hunting behaviors to another. For example, mid water predators like barracudas often attack small bait fish, and the small fish rush to the ocean floor. That gives the predators closer to the bottom, like black sea bass, an opportunity to feed on fish that may not have been available to them. So then you would have to ask, what happens if the mid water predators aren't there anymore? Would that affect the health of other predators? Understanding that interaction is important to managing the area.

Though the network issues delayed the start of the project, today Drs. Campanella and Auster were able to run sonar and observe predator/prey behaviors at the same sites. This means they can cross check data and give context to the data from the sonar. One day their research on predator behavior in the site could inform how NOAA manages Gray's Reef.


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