1. Social Sharks: Long-Term Internal Acoustic Transceivers Reveal Species Associations and Large-Scale Movements of a Coastal Apex Predator
Today I’m going to share with you some work that we have been doing tagging Sand Tigers in the Delaware Bay, and the large scale movement and species associations that we have discovered.
D. Haulsee, M. Breece, L. Brown, B. Wetherbee, D. Fox, M. Oliver
MAC AFS Annual Meeting, Lewes, DE
November 6th, 2014
Photo: National Geographic

2. Acknowledgements The Robertson’s Fund
Before I begin though, I just want to emphasize and acknowledge all of the people or groups that have been really instrumental in making any of this project happen. As you will see, this project would not have been possible if not for the collaborative efforts of many teams, and for that I am thankful.
Environmental Research and Consulting, Inc.

3. Why care about Sand Tigers?
Why Sand Tigers?
Large, apex predators, summer residents in the Mid-Atlantic ocean
Unique life history traits that lend itself to exploitation
Intrauterine cannibalism == 2 pups every other year
Slow growing
Late maturing (>2m)
Long gestation (9-12 mo)
Population decline is documented
So why do we care about Sand Tigers? Sand tigers are one of the largest top predators in the DE bay in the summer time, and have unique life history characteristics that lend themselves to exploitation. For example, baby shark fetuses in female sharks display intrauterine cannibalism, so in the two uteruses of a female shark, one fetus will develop first and then consume the rest of the developing eggs and fetuses in their womb. This means that each female only gives birth to two baby sand tigers about every other year. They are a relatively slow growing species, and mature at about 10 years old, or when they are around 6ft long. Because of this, it is hard for their populations to recover after disturbances that reduce the population. And similar to the previous figure, we can see Sand Tigers have also experienced a population decline in the last 40 years, which has lead to their population being classified at vulnerable, or near endangered.
Ferretti et al. 2010

4. Sand Tiger tagging project
Photo: Matthew Breece
To try and understand more about Sand Tigers to help mitigate their population decline, Dewayne Fox and others began acoustically tagging Sand Tigers in the Delaware Bay in Since 2007, they have telemetered approximately 300 Sand Tigers in the Delaware Bay.
Sand Tiger acoustic tagging project started by DSU (2007-current)
Since 2007, ~300 STS have been acoustically tagged in DE Bay

5. ACT Network Atlantic Cooperative Telemetry (ACT) Network
Detections from these tags were collected on receivers maintained by members of the Atlantic Cooperative Telemetry Network. On the I have a map of the current approximate locations of receiver arrays maintained by researchers along the East Coast. Through a network of datasharing, any detections of our tagged sharks on these arrays eventually made their way back to us so we could keep track of our sharks.

6. Tagging Locally, Observing Globally
Here I have a snapshot of those detections from August of 2012 to September There are a lot of detections in the Delaware Bay as you can see, but there are also a lot of receivers deployed there too. As time goes on, you will see the sharks leave the bay and head south where we get a few, but not many detections off of North Carolina and even as far south as Cape Canaveral. The winter and spring is a little boring, but in late april early may, you can see a rush of sand tigers near shore heading back north to the Delaware Bay. This high site fidelity is important for the next phase of our project.
So we know these sharks are traveling pretty far every year, but we wondered, what is the species assemblage, or social network encountered by these sharks during their annual migration? And then how do these networks change with time and space?

7. During these large scale movements:
Research Questions
During these large scale movements:
Can we use sharks as mobile telemetry assets?
What species are encountered during these movements?
So we know these sharks are traveling pretty far every year, but we wondered, what is the species assemblage, or social network encountered by these sharks during their annual migration? And then how do these networks change with time and space?

8. Or What species are Sand Tigers encountering?
So who is in a Sand Tiger’s social network, is it just Sand Tigers, or are they also detecting a variety of other marine species throughout the year?

9. Sand Tiger tagging project
Photo: Matthew Breece
In addtion to the regular acoustic tags we deployed with DSU, we also deployed an additional 20 VMTs in 2012
Sand Tiger acoustic tagging project started by DSU (2007-current)
Since 2007, ~300 STS have been acoustically tagged in DE Bay
Deployed 20 Vemco Mobile Transceivers (VMTs) summer 2012

10. How VMTs work Receiver Archival tags VMT
VMTs are capable of both transmitting, and receiving coded acoustic pings. This means that they are capable of transmitting their pings to moored receivers like the ones deployed in the DE bay, but they are also capable of recording the pings from acoustic tags implanted in other Sand Tigers, or Atlantic Sturgeon, or Striped Bass and so on and so on. In fact, there are over 65 marine species acoustically tagged in the Atlantic Ocean ranging from weakfish, to turtles to white sharks.
One key piece of information about VMTs is that they archive these records of detections, so in order to get data off of the tags, you have to get them back.
Receiver

11. VMT Internal Implantation
While previous studies have attached VMTs to the dorsal fins of sharks, we anticipated that something this big would fall off during their annual migration, so we developed a technique to internally implant these tags into the abdominal cavity of the sharks. Not only were these tags put inside of the sharks, but they were also tethered to the inside of the body wall near the incision site, keeping the tag in place. This was important because if you remember, we had to recover these tags to get the data back. That is why it is important that the sand tigers have a tendency to return to the DE bay year after year.

12. VMT Internal Implantation
So after we internally attached the tag to the shark, we sutured them up and sent them on their way. We waited a year, and in of 2013 we spent the summer actively searching the bay for any of these 20 sharks that were carrying VMTs.

13. Recapture Shark 1 Male FL: 194cm Tagged 8/24/12 Shark 2 Male FL: 198cm
And “wahoo” we actually got two of these 20 sharks to come back and get rehooked on our lines. Here you can see the healed incision sites on both sharks. Both of the recaptured sharks were males, and coincidentally they were tagged on the same day, in August Once the sharks were safely secured alongside the boat, we had to make a new incision, recover the VMT, and resuture the sharks. We did successfully for both sharks, and both sharks have since made a full recovery, although they probably really really hate me after having to have not one but two surgeries.
Shark 2
Male
FL: 198cm
Tagged 8/24/12

14. Who is in a Sand Tiger’s social network?
Percent of tagged Sand Tigers detected
Sand Tiger: 169 & 199 / 328
So, who is in a Sand Tiger’s social Network, well other sand tigers of course. Here I have plotted the percentage of tagged Sand Tigers detected by each VMT. We can see that both VMTs recovered detected over half of all of the sand tigers with acoustic tags. This means that throughout the year, these two sand tigers were really close to a majority of the sand tigers out there with tags. And this made us wonder, who were these sand tigers? Were they all males, females, a mix, juveniles adults…

15. Sand Tiger Specifics: Sex
94/116
Metadata for 227 out of 328 total Sand Tigers with tags
89/116
76/111
54/111
Percent Detected
For 227 of the 328 total Sand Tigers detected I have the sex and length information from time of tagging. Here I have plotted the percentage of those 227 males and females tagged, that was detected by both of the VMTs recovered. We see that both sharks encountered more males, but both sharks also encountered at least half of all of the females tagged that I have information for.
Female
Male

16. Sand Tiger Specifics: Sex
Shark 1
Shark 2
Metadata for 227 out of 328 total Sand Tigers with tags
Here we can look at this over time. In this plot, each vertical line indicates a detection of either a female or a male on each of the VMTs recovered. We see that both sharks encountered males and females throughout the year, you know they weren’t only hearing from females in the DE bay in the summer or something like that, but you can see again that both sharks did spend more time throughout the year with other Males. One interesting feature that does pop out is the lack of detections between late february and early May on Shark 2’s tag which we will come back to later.

17. Who is in a Sand Tiger’s social network?
Percent of tagged species detected
Sand Tiger: 169 & 199 / 328
So, who is in a Sand Tiger’s social Network, well other sand tigers of course. Here I have plotted the percentage of tagged Sand Tigers detected by each VMT. We can see that both VMTs recovered detected over half of all of the sand tigers with acoustic tags. This means that throughout the year, these two sand tigers were really close to a majority of the sand tigers out there with tags. And this made us wonder, who were these sand tigers? Were they all males, females, a mix, juveniles adults…

18. How do detections vary in time?
So how do these social networks vary over time? If I shade the time in which these sharks were likely to be within the DE Bay or the surrounding coastal waters, we can see that the majority of Atlantic sturgeon detections occur during that time although a detection of a white shark and some lemon sharks do occur during that time. During the winter, the sharks were encountering the other species such as White sharks and dogfish. If we look again at that blank area in sand tiger detections by the second shark, we now see that during that time the shark was encountering multiple atlantic sturgeon and a white shark.

19. Snapshot of a Sand Tiger’s “social network”
Atlantic Sturgeon
Lemon Shark
Spiny Dogfish
Sandbar Shark
White Shark
Striped Bass
So in summary, here is what the social network of two Sand Tigers looks like. Each circle is a node, and they are colored by species. These two nodes are like the super nodes, those are the VMTs that connect everything together. The circles are sized by the sum of detections by each VMT. The circles within the football shape in the middle are those fish detected by both VMTs while those on the periphery were detected by only one or the other. You can see that most of the sand tigers detected were detected by both sharks, and that this shark detected a loth more Atantic sturgeon than the other. Seeing how this network changes over time and space will give us insight into the life of a sand tiger as they travel up and down the coast.

20. Or Who is in a Sand Tiger’s social network?
So to answer our question of who is in a sand tigers social network, only sand tigers, or a mixture of many different species, we have found that is a mix of species, dominated by sand tigers of both sexes and various life stages.

21. Future Directions
Do the species encountered by Sand Tigers have temporal components? How often is there a change in the network, and what could be influencing those changes? Can we use supplementary location data to map where VMT detections where throughout the year? -Location records of: -VMTs detected by receivers -Other fish detected by receivers near in time to a detection by a VMT
From here, I want to look more deeply into the temporal components of this dataset to see how often is there a change in the network, and what could be influencing those changes. In addtion, I am going to use supplementary location data from the moored receievers to piece together where these two sharks were when they were detecting all of these fish.

22. Detected 29083 on 10 different days!
6 Degrees of Separation…
Questions?
Everyone in the Audience! Me
Global Green Expo Musical Guest…
Shark 2
Speaker at Expo in 2008
Detected on 10 different days!
So I would like to leave you with a story about your own social network. Everyone in the audience has now met me. I tagged Shark 2, which detected shark on 10 different days between 2012 and Now shark was tagged with the help of conservationist and TV host Jeff Corwin, who in 2008 was a speaker at the Global Green Expo in Jersey City, featuring Musical guest…
So those are your six degrees of separation from Kevin Bacon utilizing a sharks social network, and from here I’d be happy to take any questions or comments.
Jeff Corwin

23. Sand Tiger Specifics: Size
Metadata for 227 out of 328 total Sand Tigers with tags
Percent Detected
Breaking these Sand Tiger detections down by size I have plotted the percentage of sharks tagged within each size class that were detected by the recovered VMTs. Both tags appear to show similar patterns, detecting sharks that were around their size, indicated by the orange arrow, or perhaps slightly smaller. In addition, they did not encounter as many of the very large and very small sharks with tags.
Fork Length (cm)

24. Cross Talk

25. Estimates of Survival