Andrew McMains: Researching the impact of dredging on fish movement around the Rachel Carson Reserve

2022 N.C. Sea Grant & the N.C. Coastal Reserve Fellow

Andrew is a third-year PhD student at the East Carolina University (ECU) Coastal Studies Institute studying fisheries science. But how did he end up there? 

Andrew started his college career at UNC-CH studying biomedical engineering. Thanks to advice from his peers and people in the field, he believed that to be an interesting path and something he wanted to pursue. Fast forward two years and he realized biomedical engineering was not for him. He didn’t enjoy the work and craved being outside more. This prompted his decision to transfer to the University of Montana–Western to study environmental science. He loved his time there but missed the warmer weather in his home state of North Carolina. Post graduation he landed a job with the Division of Marine Fisheries. He loves fishing and knows how to drive boats, so found the job a great fit and his introduction to fisheries. From there he moved to Morehead City, NC to work at UNC-Institute of Marine Science with Dr. Joel Fodrie. That’s when he met his current PhD advisor, Dr. Jim Morley, who at the time was a postdoctoral in the Fodrie Lab. When Jim became faculty at ECU, Andrew joined his lab there as a PhD student.

The fellowship funds student research at the North Carolina Coastal Reserve & National Estuarine Research Reserve. Andrew’s research is focused in the waters around the Rachel Carson Reserve in the Beaufort Inlet. Communications Specialist, Jillian Daly, sat down with Andrew to learn more about his research.

Could you explain the project you’re working on?

"The fellowship project is looking at the impacts of sediment dredging on fish movement through Beaufort Inlet. We know that different fish species have to enter and exit the estuary at various times of the year and different stages of their life. We don’t know how dredging may impact those movements or those behaviors. Sometimes dredging can suck things off the bottom like horseshoe crabs, but we're not sure if there’s an immediate impact of dredging. We are not sure if fish are avoiding the dredge area. We’re also trying to figure out the timeframe of the impact. Say they dredge in August, do fish move differently in the area immediately? Are they behaving differently? Are there fewer fish in that area in September and October?  How long is the impact?  

Those are some of the questions we’re trying to answer with this project. Our driving question is 'Is there an immediate impact during dredging? And is the impact lasting for months on end?'"

How do you determine what fish are where in the inlet? How do you perform the research itself?

"The sampling method we used is not common, and it hasn’t been used in an inlet area before. Typically, if you’re looking at fish abundance or density, you sample with gillnets, trawling, or some way to estimate how many fish are in that area. For this project, we used acoustics, something called an ARIS, an Adaptive Resolution Imaging Sonar. Have you ever been in a boat fishing, and you see the GPS screen and next to it is the sonar where you can see the bottom and little arcs where the fish are? That’s a different type of sonar (split beam) but still sonar. 

The way the acoustic imaging works is it’s an array of 96 different sonar beams that come out of a box. The easiest way to visualize it is the box looking straight down at the seafloor, almost like a flashlight beam, or a cone of light, but in this case it’s a cone of sound. We are getting an actual image of what is down there, sort of like an ultrasound. Instead of getting a little arc of fish like you’d get with split beam or single beam sonar when fishing, we’re using all these different beams and it’s giving us an image of what’s down there. The imagery shows the shape of a fish, shark, stingray, or jellyfish. With this, we can get a good estimate of the lengths of the fish, and estimate their trophic guild (where they fit in the food web), which means that I can’t definitively say, this shape is an anchovy or a bluefish, but we can say that’s a mid water predatory fish, or that’s a benthic predator moving along the bottom, or that’s a school of prey fish.” So, we can confidently say a general trophic classification of the fish that were seeing, but can’t say exactly what fish it is, like if you were trawling or gillnetting."

ARIS sounds like an amazing technology, have people used this before for similar research?

"The technology is somewhat new. The ARIS is the second iteration of the technology by SoundMetrics. Also, it’s expensive, the set up itself is around $100K! It has been used in a few fisheries applications such as weirs on the west coast to estimate the number of salmon running back up the river. That’s the fisheries application that this technology came from. However, it is also used for military purposes to find things attached to the bottom of ships, and by law enforcement that are looking for bodies in the water, etc.  

My advisor, Jim, had used this technology in the past, and we thought we could address the impacts of dredging around the Rachel Cartson Reserve well with this acoustic technology. Before our project, it had never been used in an inlet area before but thought it would be effective in the area since it is more difficult to trawl or net in the inlet."

What have you been most surprised by with your research? 

"Beaufort Inlet has fewer fish in it than I expected. I expected a constant flow of fish in and out of the area, especially during the fall. Instead, there were plenty of days when we would sample and hardly see any fish, and that was surprising to me. However, the more I think about, I know that Beaufort Inlet is an extremely modified inlet. Inlets are not naturally 60 feet deep and as wide as the Beaufort Inlet. That's a lot of water! With that in mind, it makes sense that with an inlet that deep and wide, the fish are bound to be more dispersed. I think there are still plenty of fish there, they were just harder to see or detect than I expected."

Outreach is a key part of this fellowship. Can you talk about the outreach you’ve been a part of during this fellowship?

"I participated in SciREN, the Scientific Research and Education Network. SciREN is a graduate student-led network that connects educators and researchers. I presented my research at an event with educators and shared some of the cool imagery I’ve collected. Then, I provided ways for educators to translate this to the classroom. I also get to help out with summer camps at the Coastal Studies Institute and talk with campers about my research, fish, and what it’s like to be a fisheries scientist."

Where are you at now in the process?

"We finished our data collection in November 2022. The work now involves going through those acoustic samples that are essentially recorded as videos. I play them back through software that allows us to count the fish present. It’s a lot of me looking at videos, counting and measuring fish, and estimating the size of prey schools! We recorded about 40 hours of videos, so there is a lot to go through manually!"

Read Andrew's final report here.

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The North Carolina Coastal Reserve and North Carolina Sea Grant have established a research fellowship opportunity for North Carolina-based graduate students. The fellowship provides North Carolina-based graduate students with an opportunity to conduct research within one or more of the 10 sites that constitute the Coastal Reserve. Using the reserve sites as a research platform, fellows must conduct hypothesis-based projects that address coastal management issues specified by the Reserve. For more information and to see fellowship requests for proposal announcements, visit the fellowship page.