Bonnethead Acoustic Tracking Update

In an attempt to make good on my promise to post more frequently, I thought it was time to give a short update on what the bonnethead sharks that were tagged over this last field season have been up to. I have completed downloads on all of my receivers and I can provide some quick insights from visually inspecting the detections. I will try to provide some more concrete conclusions when I have completed analysis of the data.

First of all, I mentioned in my previous post that some of the hydrophones were placed in areas that were hypothesized to be hotspot areas for bonnetheads based on our fishing efforts. The data do seem to support this hypothesis in 2 out of the 3 receivers deployed to test it. One of these, BH 1, is our most active receiver and had over 3,000 detections in the ~2 month period it was deployed and the sharks were still around (more on this later). The second, BH 22, was only out for a period of  about 2 weeks before the sharks left and had about 300 detections. Our last hydrophone placed to test this hypothesis, BH 21, which was put out the same day as BH 22, had 0 detections. I found that one puzzling, given we caught more sharks there than we did at the BH 22 location.

As for the sharks themselves, as we had seen in our first year of data from Georgia, many sharks appeared to have a sort of site-fidelity to particular hydrophones, often the two mentioned above, but in some cases they were other hydrophones. The degree to which each shark displayed this site fidelity, however, was much more variable than what we saw in Georgia. While some sharks remained at a single hydrophone the entire period of time they were detected within our system, others chose to move around a bit. Interestingly, these movements still appeared to cluster out into combinations of hydrophones close to one another. There are of course a few exceptions, but in general sharks tagged in the western end of our array seemed to move around strictly on the western side and those tagged on the eastern side seemed to stay towards the eastern side.

I am fairly certain that the bonnetheads have moved out of our system at this point. I have two lines of evidence that lead me to that conclusion. First, I don’t have any detections after mid September. Second, I received an email from Kelsey Spencer, a graduate student at Coastal Carolina University, informing me that 3 of the bonnethead sharks I tagged had been detected in her hydrophones located on piers in Myrtle Beach, SC. These detections were actually from between 1 and 2 weeks prior to my last detection within our array, which tells me that they don’t all leave the system at the same time. It was quite exciting to get news about my sharks having passed through somebody else’s array and I hope to continue to get reports as they make their way down the coast.

First field season

I decided it was about time to give a research update, which is long overdue. I would argue that this is a reflection of how busy I have been over the last few months, being that it was my first official field season. I had also made the dual transition from having the previous 4 summers off due to being a teacher and becoming a father to my second son (a change that has justifiably been referred to as exponential, not linear). Needless to say this summer was a major adjustment for me. All of this to say that I hope to be able to make more regular posts from this point on.

The majority of this first field season was spent setting up for the acoustic tracking of bonnetheads, which is the main component of our study funded by the NC Aquariums. This study aims to understand residency patterns, movement and habitat selection of bonnetheads in local estuaries. Before I go through the specifics of experimental design and methods, I would like to acknowledge that a parallel study was designed in Georgia by my advisor Dr. Joel Fodrie, our lab manager Matt Kenworthy , as well as our collaborator from UGA, Dr. Jeb Byers. Being able to learn from what they did in Georgia was paramount to my success here in NC, allowing me to “stand on the shoulders of giants,” as they say.

Th20160531_111034e first step in the experimental design is to deploy the acoustic receivers (shown left labeled and covered in duct tape), also known as hydrophones. We used 22 Vemco VR2W hydrophones, which have an average detection range in our system of 350m, line of sight. We arranged the hydrophones around the estuary in areas we hypothesized were likely important a priori, in addition to a few that were placed in areas we hypothesized might be hotspots for bonnetheads based on our tagging efforts (more on this later). It should be noted that our array (displayed below) is complemented by over 50 other hydrophones within our estuarine system employed in studies on juvenile gag grouper (UNC) and weakfish (NC State).

BH Array

Once the hydrophones were out, the next step was to focus on tagging animals. My efforts began with a trip down to the Skidaway Institute of Oceanography (SKIO), where I led an effort to tag 8 additional bonnetheads for the parallel study previously mentioned. This was essentially a replication of the tagging efforts from the previous year, when the study began. Now, I’ll begin by saying that I was unsuccessful in tagging the 8 bonnetheads. I had gone in with the expectation that it would be an easy task, based on stories of plentiful bonnethead sightings from the previous year. Suffice to say we didn’t have the same expe20160616_083336rience this year. I did learn a great deal about the marsh systems down there and about organizing field expeditions in general, which was a new experience for me. On our final day we aDSCN6698dapted our fishing strategy after a lot of trial and error and were able to capture and tag 2 bonnetheads (pictured left with Max Tice-Lewis, another student in my lab), which allowed us to have some sense of success before returning. Luckily, Matt Kenworthy was able to get the job done a couple months later when he visited SKIO (pictured right).

Upon returning to NC I immediately began going out fishing for bonnetheads. On our second trip, we captured a bonnethead just to the north of our usual drone survey study site across from Duke Marine Lab (DUML)20160624_163848, which was very exciting(pictured left with lab tech Rich Mahoney). Despite this, nightfishingmany of the early trips yielded no bonnetheads. I did, however, learn quite a few things about fishing in these early expeditions. We finally got our second bonnethead on a night fishing trip in the same area as the first one a few weeks later (pictured right with Matt Kenworthy).

A few days later, I had the most succeboatpicssful tagging day with 9 bonnetheads captured (pictured left with Seth Sykora-Bodie from DUML). I credit the information about where I targeted fishing that day to UNC-IMS Paerl lab research technician and experienced fisherman Jeremy Braddy. This was followed by a 2 week pause as I had my second child. When I resumed my fishing efforts, the bMiddle Marsh 2onnetheads seemed to be much more available, with each day spent fishing yielding at least 2 bonnetheads caught. I would like to credit this to my increased knowledge of fishing, however seeing them in the same areas where we got skunked before (such as in Middle Marsh, pictured right) leads me to believe that their numbers may have increased later in the season, as I had heard from another experienced bonnethead fisherman, John Mauser from NC Aquariums.

We have already received report of a recapture of one of our tagged sharks (pictured left with Eric Kimage1ramer and Alisha Hawkins), which was released alive. This adds to the reassurance from 2 of our tagged sharks in GA surviving over a year that sharks tagged here will likely provide us with lots of data to analyze as they swim around in our array for the next year. Our first download is next week and I can’t wait to see what our sharks have been up to!

 

 

White shark necropsy

On Monday, my advisor informed me that there was a white shark that had washed ashore on Wrightsville Beach and wondered whether I had any interest in driving down and collecting it. Although I was rightfully skeptical due to having an experience of driving 2 hours to collect a shark that was no longer there during my Masters at Stony Brook, I couldn’t help but get excited. I immediately called the number he gave me and followed the telephone chain that had brought the message to me, but by the time I was speaking to somebody in the immediate vicinity, I was told the University of North Carolina at Wilmington (UNCW) had already collected the shark. I would soon find out this was probably for the best, but my immediate reaction was that another one had slipped through my fingers. Nonetheless, I was hopeful to be able to lay eyes on the specimen, being a UNCW alumni I felt that I at least had a shot at it.

I was fairly busy that day so my attention quickly turned back to the work at hand. By the end of the day however, through word of mouth, I had gathered that the necropsy would be held the following day at 1pm and that my former Ichthyology professor, Dr. Thomas Lankford, was one of the people involved in directing this event. I immediately began using every means of communication I could think of (phone, text, email) in order to try to get through to Dr. Lankford to get a spot at the necropsy. I would soon find out this wasn’t necessary as it would be open to the public, but my efforts would provide me a more “insider” perspective. By 8:45pm I had secured my spot as well as a ride, thanks to Chuck Bangley from East Carolina University (ECU).

Chuck and a fellow ECU undergraduate DJ Evans picked me up the morning of the necropsy and we made the 2 hour drive down to Wilmington. We arrived with a few minutes to spare and as we pulled into the parking lot, I saw a crowd of students and reporters around a building, which I immediately knew would be where we were heading. We made our way towards the Oriole Burevitch Laboratory and as we turned the corner beside Friday Hall, we knew we were heading in the right direction by the fresh scent of dead shark and the student walking the other direction with a look of distaste on her face. Another student pointed us towards the building, where we saw the shark being lifted in with a crane. Immediately I realized the scale of the shark I was about to see was one I had not had the opportunity to work with yet.

20151208_13281920151208_131126 We quickly pushed our way through the crowd of almost 100 students and found Dr. Lankford, who directed us inside the building. While the UNCW marine mammal crowd, headed up by William McLellan (WAM), prepared for the necropsy, I did my best to jockey for a good vantage point. I immediately noticed t20151208_131230hat the shark had been damaged, particularly on its underside. Some would speculate that the pectoral fin might have been c20151208_134754ut off, but Dr. Lankford felt it was most likely bitten off after the animal had been deceased. Both Dr. Lankford and WAM (pictured to the right – Dr. Lankford with a white baseball cap and WAM with a darker hat behind him) seemed to waste no time, immediately getting to work cutting into the animal.

The an20151208_134857atomy of a shark was familiar to me as I had some experience running dogfish dissections as a High School teacher, but as I mentioned before the s20151208_135031cale was unfamiliar. Seeing the size of the liver that kept this animal afloat really made you appreciate just how massive it 20151208_140015was. As the liver was removed the digestive tract became visible, which we were told by WAM had something of substance inside of i20151208_135714t. It was sometime around this point when one of the faculty told his child to have a look inside the body of a white shark, he might not get another opportunity in his lifetime to do this, which I realized was probably true for all of us. The intestines were quickly cleared out of the way in order to move on to other parts of the body, but we knew that we would eventually get a chance to see what was in the stomach.

20151208_140841The next area that was explored was the gill arches, which revealed some parasites, but these were not considered to be unusual and probably did not lead to the death of the animal. As WAM continually cut away at the animal, more o20151208_141615rgans were revealed, one of the most notable being the 20151208_141746heart, which caused quite a lot of excitement for the marine mammal crowd, who were not used to seeing so many valves on a heart. About this time, somebody dropped one of the fins right in front of me. The clean cut on this fin reinforced the idea that the missing pectoral fin was not cut off, but actually bitten off as Dr. Lankford had hypothesized.

Now th20151208_142527e white shark really began to be re20151208_145604duced into pieces as the vertebral column began to be cut into sections and cleaned off. This is when Dr. Lankford asked if I would like to have an opportunity to participate, which I took, seen right (photo credit: DJ Evans). Little by little, all of the vertebrae were cleaned of any flesh and the finished product was lined up with the head of the shark for an incr20151208_151146edible photo-op. The head was then cleaned off, with jokes bei20151208_151938ng made about the shark receiving dental services, which I think also provided quite the photo-op. This was the view of the shark that reminded me of what an incredible predator it must have been before whatever tragedy befell it occurred.
On that no20151208_153319te, we return to the question most of us couldn’t wait to h20151208_153545ave answered, “What was in the shark’s stomach?” The table got extremely crowded again as the digestive and reproductive tract re-emerged. As the stomach was being cut into, I was eventually able to get a view of the digested remains. At first they were indiscernible to me, but as the bones were cleared from the rest of the digested tissue, it 20151208_154150quickly became apparent that we were dealing with a large bony 20151208_154402fish. The presence of
pharyngeal teeth led Dr. Lankford to hypothesize that it had eaten a large black drum. While going through the bones, DJ recognized two circular pieces as otoliths. They were too large for anybody else to recognize as such and were almost thrown out!

20151208_154802When examining the esophagus, WAM noticed some lesions, which he had seen in pilot whales he had necropsied. While indicative of trauma, he did not feel these were significant enough to cause mortality. Finally, the spiral valve was opened up, which proved to be an interesting sight. These organs are used to increase the surface area of the shark’s re20151208_161234latively short digestive tract to allow for increased nutrient
absorption.

While the cause of death could not be determined from the necropsy, UNCW researchers thought it would be interesting to look at environmental variables that might have caused the animal distress. The vertebrae and tissues would be sent off for further analysis to help better our understanding of these elusive and mysterious apex predators. Leaving the necropsy I was left with a sense of amazement at how no part of the shark was simply tossed away and each part served to teach not only the students present, but also the faculty present and the researchers receiving samples, about the white shark that washed ashore in our neck of the woods.

Drone surveys

Unmanned Aerial Systems (UAS) or drones have been getting a lot of media attention lately as regulators attempt to keep pace with the quickly evolving technology. This technology brings exciting prospects to everything from agriculture and mining operations to emergency response situations, not to mention the fun to be had by hobbyists. For scientists, the technology has often felt out of reach as the use of drones for research falls under commercial use, which has strict guidelines for reporting unlike the recreational users who still have virtually unrestricted freedom to play.

Thanks to Dr. Dave Johnston and the Unmanned Systems Facility at DUML, that technology has become available to many scientists, especially in our area. As part of our bonnethead study funded by the NC Aquariums, we included Dr. Johnston and his lab in order to test this exciting approach to see if we could use it to monitor our sharks. As mentioned in an earlier post, we designed a set of experiments to test the conditions that would lead to optimal detection of the animals in specific habitats of interest.

Once we had finished making our decoys (see earlier post), it was time to fly the drones to take images of the decoys. First we had to determine if the decoys could be seen at the surface. Have a look below and decide for yourself, these images are taken with regular (RGB) and Near-Infrared (NIR) cameras.

RGB - surfaceNIR - surface

Did you spot them? Pretty hard to miss actually, which was reassuring, but we had to ask ourselves at this point, would real sharks show up on the camera like this? Since we didn’t have access to a real shark to place in the field with our decoys, we had to think of another way to test this and ensure that the decoys weren’t unrealistically representing the way a shark would appear on the camera. Luckily the aquarium had a bonnethead in a tank that was not on display and the staff there were gracious enough to allow us to place our decoy in the tank with the shark to take some pictures side by side. We decided the NIR camera would be best as it seemed to provide the most contrast with the water.

Near IR comparison

Seeing the shark and the decoy side by side really helped us to appreciate how promising the use of this technology would be for our research. With these preliminary conclusions, we felt we could move from the question of “can we see them(?)” to “in what conditions can we see them?” This was an exciting first step to what could turn out to be a pioneering study of the use of UAS to study sharks.

 

Shark decoys

Although I spent some time working in construction during high school, I never imagined I would end up in a career that involved woodworking. Not to sound condescending, I actually like working with saws! Little did I know, however, that I would need to make 2-D representations of sharks for a research project.

Part of the research project on bonnetheads is to see if it is possible to monitor these sharks from aerial drone surveys. In order to test this we have designed a set of experiments that will first determine if the sharks would be recognized in the drone footage and if so, find optimal conditions for doing so. In order to carry out these experiments, we needed to have something that looked like our shark, but that we could manipulate and control.

We went through a couple different ideas that were quickly thrown out due to time and funding constraints, such as 3-D printing, taxidermy, etc. We finally decided that painted encapsulated plywood would probably make a fine silhouette for us to spot from the drone. In order to make this though, we needed some measurements, or, as we would soon find simplified things, something to trace.

shark 9

Lucky for us (not so lucky for the specimen), a pregnant bonnethead meant to be placed on captive display succumbed to the stress and we had an opportunity to sample her before she was dissected for a necropsy. She provided the original cut out that would be used to make our silhouettes. Her traced outline proved very valuable, although I had to endure the scent of dead shark in my office for several days before the decoys went into production.

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Once we had our materials, we (Tatyuanna Williams, a student mentee from West Carteret High is pictured above) proceeded to cut the outline of our shark out and used that to trace the outline onto plywood. Under the guidance of Capt. Stacy Davis, Austin Moore (an undergraduate at Virginia Tech doing a semester at DUML, pictured below) and I used power saws to cut the outline out of the plywood. Fins were screwed into the main body cut-out.

20150922_110240

We then used Epoxy to cover the shark cut-outs in order to protect them from the water they would go in. This took a day to dry and then we sanded the finish in order to provide better adhesion for the paint. We spray painted and out came our finished product. I think they look pretty good, if they aren’t detected by the drones we can at least use them as decorations!

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