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Center for Marine Sciences and Technology (CMAST)

Spot a Shark

I am the project manager for Spot A Shark USA – a citizen scientist program that aims to better understand sand tiger shark Carcharias taurus populations along the Atlantic coast. SCUBA divers are asked to photograph the sand tiger sharks they encounter on their adventures and post their images to the Spot A Shark USA website. My team of aquarium scientists and students then uses Wildbook® software to map the unique spot patterns visible along the sides of the photographed sharks to identify individual animals.

Popular in aquariums because of their fierce appearance but relatively docile nature, sand tiger sharks are valuable ambassadors to spread awareness for threats to sharks and rays. Globally, sand tiger shark  populations have experienced significant declines. They are listed as vulnerable on the IUCN Red List of Threatened Species, and as a species of concern by the National Marine Fisheries Service. In the US, recreational and commercial fishing are prohibited, and this species is ranked as highly vulnerable to climate change impacts and habitat disruption.

Waters off the North Carolina coast are important for sand tiger sharks year-round. It is known that many of the shipwrecks in the ‘Graveyard of the Atlantic’ are known aggregation spots for sand tiger sharks, but the extent to which the species relies on this habitat is uncertain. Importantly, pregnant sand tiger sharks are found here during summer, fall and winter, suggesting a key role of this habitat in their reproductive ecology. The North Carolina Aquariums have made progress towards understanding sand tiger shark habitat use in the northwestern Atlantic. We have over 850 individual sharks in our photo library, with 35 sharks that have been photographed on more than one date. Repeat records of even more individual sand tiger sharks will help track their movement and behavior over time.

Shipwrecks off the North Carolina coast – like the USCGC Spar shown here – are important habitat for many fish species. Sand tiger sharks are often found in large aggregations at some sites, but presence and abundance vary seasonally. We are using the data from Spot A Shark USA to learn more about how sand tigers use wreck habitats. I am curious…where did they hang out before there were so many shipwrecks? (Photo by Mike Gherkin)
The spots along the sides are clearly visible on this female photographed at the wreck of the Dixie Arrow, off the Outer Banks of North Carolina. The large belly and mating scars around the pectoral fin indicate this female may be pregnant. We believe NC is an important area for female sharks, but little is known about where and when mating occurs. Sand tiger sharks give birth to live pups, but we do not know where females go to give birth. (Photo by Shawn Harper)
We work closely with many people in the NC dive community. The NC Aquariums produced simple guidelines to explain how divers can safely photograph sharks and easily upload their images to Spot A Shark USA.
Divers should approach sand tiger sharks from a safe distance to photograph them from the side. Sand tiger sharks are docile and tolerant of humans, making them a popular species to dive with off our coast. The North Carolina Aquariums is excited to offer divers a chance to enhance their experience, by allowing them to connect to sand tiger sharks through Spot A Shark USA. (Photo by Mike Gherkin)
Some divers use hi-tech camera equipment to photograph sharks and other marine life. However, many divers send us pictures taken with GoPro cameras. You don’t need fancy gear or magazine quality shots to get great pictures that we can use for photo identification. (Photo by Tanya Houppermans)
Spot A Shark USA relies on a large network of partners and scientists. For example, the dive team from Georgia Aquarium has contributed hundreds of shark images. They added over 100 sharks to our photo library.
Sand tiger sharks are often photographed with other small fish species around them, like the tomtate in this photo. (Photo by Tanya Houppermans)
Kirsten Boleyn (Semester at CMAST 2019) was the first Spot A Shark student intern. Each semester, students learn how to upload shark pictures, map spots and match new encounters with sharks in our photo library.
Every photo submitted is viewed by me or other Spot A Shark processors. We verify the species, determine the gender if possible, and double check that the date and location are entered correctly. The next step is to manually map the spots on the side of the shark.
The uploaded images of sharks are processed using methods established by the Wildbook developers. We define the area we are going to view and use a box to make the image level. Next we designate where the dorsal and pelvic fins are for reference. The final step is to place dots over the spots on the shark. This makes a unique constellation for each animal that can be saved and used for comparison to other sharks.
The Spot A Shark algorithms compare spot patterns to find possible matches. It is still up to the human eye, however, to make the determination about whether we have matching spot patterns. We use two different algorithms, the Modified Groth and the I3S, to pull out potential matches. Then we do a careful comparison to make a final determination.
We are fortunate to partner with talented photographers. While we can’t use this picture for spot mapping it’s always a joy to see these amazing animals close up. There is much to learn as we continue to conduct research and for conservation of this and other shark species. (Photo by Mike Gherkin)
Sand tiger shark USA-R0128 is pictured here. He is a young male that was photographed 7 times on the wreck of the Aeolus in 2019. (Photo by Tanya Houppermans)