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Whale shark study assesses population

Photo identification of whale shark spot patterns recorded by researchers and citizen scientists across decades and throughout the Western Central Atlantic has provided the region’s first population estimate and highlighted migratory patterns of the world’s largest fish, an iconic ambassador for sharks and other marine wildlife.

The study, published by PlosOne entitled “Long-term assessment of whale shark population demography and connectivity using photo-identification in the Western Atlantic Ocean”, is timely as whale sharks were recently elevated to the status of Endangered to Extinction per the International Union for the Conservation of Nature, due to population declines recorded globally. Generally solitary, whale sharks aggregate seasonally at certain sites to feed on available food.

Researchers and citizens aiding in science research are able to locate these whale sharks at these sites, taking advantage of the rare times when whale sharks gather in large numbers. By observing the unique pattern of spots on the whale sharks researchers have been able to record 1,361 individual whale sharks between 1999 and 2015, deriving a population estimate ranging from 1,600 to 2,900 animals of primarily juvenile males that inhabit the Gulf of Mexico, the Caribbean and the western Atlantic ocean.

The study’s lead author, Jennifer McKinney with the Louisiana Department of Wildlife and Fisheries, notes that the study is the first of its kind to demonstrate “both a population assessment and the regional connectivity of whale sharks using a non-invasive method of studying the patterns of its unique spot patterns”.

McKinney additionally stated, “My colleagues and I have been observing the repeated use and movement between multiple aggregation sites by numerous whale sharks throughout the region, and we are excited to share this information with the public and wider scientific community.

“In terms of whale shark studies, I think it’s really important to broaden your scale so that is appropriate for the whale shark ecology and this paper really highlights the fact that we have a single population of whale shark in the Western Central Atlantic.”

Providing a strong validation of the utility of spot pattern matching for regional population and migratory studies in a range of species, the Wildbook platform ( hosts the global whale shark citizen science database ( founded by Jason Holmberg and used in this study.

Mr. Holmberg notes “These results establish the Gulf of Mexico and Caribbean among the most informative and rewarding areas to study the world’s biggest fish, the whale shark. The connectivity among multiple locations is now evident thanks to the deliberate and careful planning and coordination by teams in several countries, and our study highlights the need for conservation across borders for this rare and endangered species. I hope to see more research groups for migratory wildlife adopt this model of common data standards and tools, data sharing, citizen science inclusion, and close collaboration in the Cloud.”

In the context of the species’ conservation and next steps, “We need to redouble our efforts to establish broad alliances across boundaries and between sectors to help whale sharks thrive despite mounting threats from growing tourism, shipping, oil exploration, and in our region, fisheries for their food.

It is imperative that we scale up our standardized work to reverse declines of what is essentially a very small population, and in human terms could fit into a movie theatre complex” noted Dr. Rachel Graham, Founder and Chief Scientist of MarAlliance, who has studied whale sharks for two decades and provided guidance in the related encounter tourism and many of the first photo identification images that enabled the long-term tracking of individual whale sharks throughout the region.

Whale shark facts and information

  • Whale sharks eat zooplankton, jellyfish, fish eggs and tiny pelagic baitfish, reach sexual maturity in their 20s and are thought to live to be over 100 years old.
  • The techniques for confidently matching whale sharks’ unique spot patterns were based on star-watching and matching algorithms developed by NASA.
  • Whale sharks are protected from international trade by the Convention on the International Trade for Endangered Species of Fauna and Flora (CITES) and by national legislation in several but not all countries that they visit in the western Atlantic region.
  • Whale sharks were recently elevated to the status of Endangered to Extinction per the International Union for the Conservation of Nature, due to population declines recorded globally.
  • Whale sharks generate US$ millions annually through encounter tourism conducted at aggregation sites.
  • The whale shark identified as H-21 and highlighted in this study is a true shark ambassador and continues to show his spots around the Gulf of Mexico after multiple sightings in Belize, Honduras, Mexico and the US, was resighted again in Mexico this week, increasing our tracking data from 12 years to 17 years. This shark was first recorded by Dr. Graham in Belize in 2000.

All members of the public can participate in the whale shark citizen science by uploading their sightings to is developed by the Portland, Oregon–based nonprofit Wild Me ( as part of the joint Wildbook™ project, which includes biologists, data scientists, and computer vision researchers. Contact:

MarAlliance is an international research and conservation NGO that explores, enables and inspires positive change for threatened marine wildlife, their critical habitats and dependent human communities. Contact:

Article written by: Jennifer McKinney