Finprinting

The whale shark (Rhinocodon typus) is the largest shark species alive today, reaching lengths of 18m. Yet, it is not just their size which makes whale sharks so recognisable... they have remarkable patterns of spots and stripes, which are as unique to each shark as a fingerprint is to a human. Not only does this make these animals startlingly beautiful, but can also aid scientists studying these sharks. So how do you fingerprint a shark? How do scientists use their identifiers? And what have we learned as a result?

Their spots and stripes are as unique to a whale shark as a human fingerprint (Image Credit: Derek Keats / WikimediaCommons)

Take My Picture

As there are so nomadic and wide ranging, it can be very challenging to study large marine animals like whale sharks. However, photographic identification (photo-ID) has been used successfully to identify specific individuals in several other species, including turtles, whales and dolphins, in order to track them through time and space. It is similar to tagging studies, but not as invasive (Speed, 2006; Brooks et al, 2010; McCoy et al, 2018).

Ecotourism to snorkel and dive with whale sharks is popular throughout their range (Image Credit: Tatiana Nurieva / Shutterstock)

As whale sharks are sedate, not a threat to humans and the target species for many ecotourism companies, photo-ID data can even be collected by the general public. In fact, scientists are now collecting whale shark ID images through citizen scientist initiatives - where eager members of the general public submit any photos they capture of these gentle giants, for use in scientific research. This can generate very large powerful datasets, for minimal cost, and get people involved and interested in the science Speed, 2006; Brooks et al, 2010; McCoy et al, 2018).

Whale sharks are docile and safe to dive with, so many photos are taken of them every year, from all over the world (Image Credit: DJ Mattaar / Shutterstock)

A Unique Finprint

When an image of a whale shark is submitted, scientists can use a specialised software called I3S to map that shark's spotty and stripey markings. This program highlights the unique pigmentation patterns on the flank of the shark, near the gills, known as a "dorsal fingerprint". These fingerprints can then be saved and used to match other images to, in order to identify when a specific individual is seen again in the future (Speed, 2006; Brooks et al, 2010; McCoy et al, 2018).

Photo ID fingerprints are taken from a region on the flank near the gills (Normal et al, 2017)

If these fingerprints are saved to online shared databases, they can be used by scientists all over the world to track the movements of specific whale sharks (Speed, 2006; Brooks et al, 2010; McCoy et al, 2018).

Wildbook for Whale Sharks does just that. This online resource allows the general public to become involved in photo-ID collection and the data can be used anywhere! (Speed, 2006; McCoy et al, 2018). Check out Seeing Spots for more info.

Whale shark fingerprints can be run through software to be matched to future photographs. This allows scientists to identify and track individuals throughout time and space (Normal et al, 2017)

Who's Who?

One research project that has come out of this initiative allowed scientists to study the demographics of the whale shark aggregation at Donsol, in the Philippines. Thanks to the photos taken by all the ecotourist during their snorkeling and diving excursions, the experts learned that this region supports some 1,767 individual whale sharks (McCoy et al, 2018).

A citizen science photo ID project has identified that whale sharks repeatedly return to a region in the Philippines to breed [INDIVIDUAL SHARKS = DOTS, SIGHTING YEAR = COLOURS] (McCoy et al, 2018)

The ID fingerprints also allowed the researchers to discern a pattern in the whale sharks' behaviour; Identified sharks were seen repeatedly year after year, with some even returning to the site consistently for 10 years! This ability to return to a very specific location repeatedly, even after disappearing on long migrations in the mean time, is known as "site fidelity" or "philopatry" (McCoy et al, 2018).

As the scientists also learned that whale sharks in the Philippines are generally larger than those seen at many other sites, with the majority being sexually mature sharks, they concluded that this region might be used for mating or "pupping" (giving birth to young). This is very exciting and important, because scientists have yet to find the elusive whale shark mating grounds! Whatsmore, as these sharks are flagged as Endangered by the IUCN, it is especially critical to locate and protect their breeding habitats (McCoy et al, 2018).

Software can be used to recognise inidividual whale sharks once their unique markings have been stored in a database, so their movement can be tracked when they are resighted (Speed, 2006)

United We Stand

This study highlights how citizen scientist initiatives can have incredible valuable! As the scientists collaborated with ecotourism businesses and the general public to conduct this research, they were able to collect much more data than they ever could have done on their own, and therefore, they could learn so much more (Gallagher & Hammerschlag, 2011).

Whale sharks are the only species of sharks to have both spots and stripes on their skin (Image Credit: Elianne Dipp / Pexels)

Also, initiatives of this kind can be critical for engaging the general public and local community to take interest in sharks. During this work, members of the public's submissions to Wildbook for Whale Sharks were responsible for the identification of 12 new whale shark individuals! It's pretty cool that members of the public can get involved in science in this way! (Gallagher & Hammerschlag, 2011; McCoy et al, 2018).

If you are ever lucky enough to see a whale shark in the wild, you too can become a part of the scientific data collection team by submitting your photographs at to Wildbook for Whale Sharks.

As whale sharks are flagged as Endangered by the IUCN, it is vital to locate and protect their breeding habitats (Image Credit: Andrea Izzotti / Shutterstock)

References

Brooks K, Rowat D, Pierce SJ, Jouannet D & Vely M (2010). Seeing spots: photo-identification as a regional tool for whale shark identification. Western Indian Ocean Journal of Marine Science, 9:2. Access online.

Gallagher A & Hammerschlag N (2011). Global shark currency: the distribution, frequency, and economic value of shark ecotourism. Current Issues in Tourism, 14:8. Access online.

McCoy E, Burce R, David D, Aca EQ, Hardy J, Labaja J, Snow SJ, A Ponzo & Araujo G (2018). Long-Term Photo-Identification Reveals the Population Dynamics and Strong Site Fidelity of Adult Whale Sharks to the Coastal Waters of Donsol, Philippines. Frontiers in Marine Science, 5. Access online.

Norman BM, Holmberg JA, Arzoumanian Z, Reynolds SD, Wilson RP, Rob D, Pierce SJ, Gleiss AC, de la Parra R, Galvan B, Ramirez-Macias D, Robinson D, Fox S, Graham R, Rowat D, Potenski M, Levine M, Mckinney JA, Hoffmayer E, Dove ADM, Hueter R, Ponzo, Araujo AG, Aca E, David D, Rees R, Duncan A, Rohner CA, Prebble CEM, Hearn A, Acuna D, Berumen ML, Vázquez A, Green J, Bach SS, Schmidt JV, Beatty SJ & Morgan DL (2017). Undersea constellations: the global biology of an endangered marine megavertebrate further informed through citizen science. BioScience, 67:12. Access online.

Speed CW (2006). An information-theoretic assessment of spot-pattern matching software and its application to population estimates of whale sharks (Rhincodon typus) (Doctoral dissertation, BSc thesis, Charles Darwin University, Darwin). Access online.

By Sophie A. Maycock for SharkSpeak