Photo ID software helps unveil whale shark movements


April turned out to be a bumper month for whale shark sightings this year, with sightings almost every day, and we were lucky enough to collect a fantastic amount of photos and videos, both taken by ourselves and donated to us by members of the public. This has been extra exciting for us at the Whale Shark and Oceanic Research Center, in part due to our recent submissions of whale shark photographs to the global identification database called Wildbook for Whale Sharks (www.whaleshark.org). This database uses computer software originally created by NASA to analyse objects in the night sky to identify whale sharks by their distinctive, individual spot patterning. Our photos have produced an abundance of positive matches and re-sightings, as well as new individuals that have never before been identified in the database. It has been very interesting to learn that some of the whale sharks we have seen on different trips throughout this most recent season have in fact been the same individuals, demonstrating that these whale sharks are remaining in the vicinity of Utila for longer than previously documented.

 

One of the best examples we have is a whale shark identified by Wildbook for Whalesharks as H-105. We recorded four encounters with this shark in Utila between 25th March and 2nd May, showing a residency time of over five and a half weeks. To our knowledge, this is the first record of a whale shark remaining in the vicinity of Utila for such an extended period of time. A scientific paper published in 2013 found that average residency times here are in the order of 12 days. To see that whale sharks are staying around the island for longer is encouraging.

 

However, on our first two encounters with this particular shark H-105, it was unmarked. Then, on the third encounter we observed a small but obvious scar on the top of the dorsal side, just behind the head. When we encountered it the fourth time, the scar was smaller as it was healing but still unmistakably there. A number of whale sharks have large and obvious scarring on the dorsal side and fins, a large number of which are thought to come from boat strikes and propeller damage.  Boat strikes are an unfortunate inevitability with increased marine traffic and targeted whale shark excursions, but to know the whale shark was injured within the area and within the time period that we observed it is concerning.

 

Here at WSORC we abide by and actively promote the Honduran responsible encounter guidelines, set out after a collaborative effort between the government and WSORC in 1999 as a way to regulate both in-water interactions with the whale sharks and boat activities within their vicinity. With increased acceptance of and adherence to these regulations it is hoped negative human-wildlife interactions with whale sharks will decrease. Their behaviour is not well-studied over long time scales but it is probably a fair assumption that if an animal has repeated stressful or harmful experiences in a specific area it will be discouraged from returning there in the future. This is something WSORC are working hard to avoid.  As the largest living fish in the worlds’ oceans, whale sharks form a major source of economic wealth here in the Bay Islands. They are a huge tourism attraction and are a true privilege to encounter.

 

Another more positive revelation we have had from submitting these photos to the global database is the identification of an individual that has been spotted here in Utila almost every year since 2005, and also in Gladden Spit, Belize! Confirmed re-sightings of individuals over this kind of time period is key to understanding their life histories, migrations and behaviours over their lifetimes. Hopefully there will continue to be responsible encounters with whale sharks around Utila that yield photographs and videos, enabling us to contribute more information to the database. It is exciting to think how much can be learned about these amazing animals from the numerous encounters that occur here and it is one of our priorities to collect sightings data from other people and organizations around the island. Who knows what the next encounter may reveal about these enigmatic creatures…

 

For more information about the global sightings database: http://www.whaleshark.org/

 

For more information on the residency times of whale sharks in Utila: http://onlinelibrary.wiley.com/doi/10.1111/jfb.12195/abstract;jsessionid=6ED81EF0B4196EA4564E7F753C863CD2.f03t01?deniedAccessCustomisedMessage=&userIsAuthenticated=false

 

 

For more information about the identification software used by Wildbook for Whale Sharks:

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2664.2005.01117.x/full