Undersea Constellations: The Global Biology of an Endangered Marine Megavertebrate (Whale Shark) Further Informed through Citizen Science

It is challenging to gather ecological data including behaviors and movements on worldwide animals. Such data is gathered from multiple sources because it would be impossible for one group of scientists to collect such data on such a large spatial scale. One approach that has been helpful is citizen science, the collection of data from the general public, which has helped increase our knowledge on animals that inhabit global spatial scales. With such data we can access the abundance, size, sex frequency, and spatial trends of Nursey sites, mating sites, and feeding hotspots of such animals that can help us to better manage and protect a species. An example of an animal that is of critical importance to obtain such data would include the Whale Shark (Rhincodon typus).

Little is known about the Whale Shark, and the knowledge we have on the animal has been recently documented in the past decade. They filter-feeders that aggregate in groups at specific locations throughout the oceans where there is much Planktonic growth, and are distributed between 30°N and 30°S. Their life history includes slow growth, later maturation, and extended longevity, which makes them vulnerable to population declines especially to human threats including bycatch, pollution, ship strike, and targeted fishing which is why it is critical to obtain such spatial data. Ecotourism activities have focused on monitoring such sharks via photo-identification, observing unique skin patterns, thus creating a database of photo-identified sharks. This study reports the success of monitoring the Whale Sharks on the global scale which includes sightings on local and global levels, size and sex ratios over time, locations of common resighting history, and the resighting of individual sharks in one or more countries. 

Figure 1. Unique pattern behind the gills helps identify individual

Photo-identification images are collected when a tourist or a researcher is swimming and takes a picture of a skin pattern that is unique to each individual shark that are long lasting. An example is seen in Figure 1. Such pictures are then uploaded to a database online as well as other information including sight location, sex, and estimated length. Computer-assisted pattern-matching technology is used to determine if the shark is a new shark or if it is a resighted shark. Each encounter is assigned a location code, depending on the country or hotspot where the encounter, or sighting, occurred. Identified sharks are catalogued with a prefix according to the location code from the first identifiable sighting and each newly identified shark is assigned a unique number specific to that sighting location.

Figure 2. Hotspot Distributions of Whale Sharks

From 1992 to 2014 there has been 28,776 whale shark encounters, and 6091 individual sharks have been identified from 54 countries. The authors of this study determined 20 hotspots, or locations that had at least 100 whale shark encounters, which have contributed to 99% of all the documented encounters. As seen in Figure 2, such hotspots include Belize, The Maldives,  South Africa, Tanzania, Mexico–Atlantic region, Honduras, Mozambique, Qatar, Western Australia (Ningaloo Marine Park), The Philippines (Donsol, Leyte, Cebu), Seychelles, Djibouti, Oman, The United States–Gulf States region, Christmas Island, Mexico–Pacific region, Indonesia, Thailand, Red Sea, and The Galapagos. Much of these sites have been identified with the help of the general public including ecotourism activities. Such sightings have been correlated with areas of high primary productivity of plankton. 

Figure 3. Sex ratio of identified whale sharks at global hotspots

As seen in Figure 3 there seemed to be a strong male bias throughout 14 of the previously mentioned hotspots, with at least 66% of the individuals being males. However, at the Galapagos, 99% of the individuals were female, at the Red Sea, 75% of the individuals were female, and in Thailand, 68.5% of the individuals were female. There is also a bias of the juvenile inhabiting the coastal areas. 

Table 1. Average total length

According to Table 1 the longest individuals occur at the Galapagos with an average length about 11.07 meters, followed by the U.S-Gulf States region with an average length of 8.01 meters, Belize with an average of 7.21 meters, Mexico-Atlantic region with an average of 7.12 meters, and all other locations with an average of 7.0 meters. 

Based on the data, the whale sharks tend to be found in localities throughout the year and some may even stay in the same area for an entire year. However, most Whale shark aggregations are very seasonal in which ecotourism activities try to take advantage of. The overall average of sharks returning to the same hotspot within 2 or more years is about 35.7%.

Based on photo-identification, marker tags, and satellite tracking Whale Sharks tend to migrate between local countries, maybe like 1000 km. There are only very few exceptions where the whale sharks migrated across entire oceanic basins. Not much is known about their reproduction, however, many pregnant females are found in offshore habitats, suggesting such areas provide pupping and nursery grounds.

Citation
Bradley M. Norman, Jason A. Holmberg, Zaven Arzoumanian, Samantha D. Reynolds, Rory P. Wilson, Dani Rob, Simon J. Pierce, Adrian C. Gleiss, Rafael de la Parra, Beatriz Galvan, Deni Ramirez-Macias, David Robinson, Steve Fox, Rachel Graham, David Rowat, Matthew Potenski, Marie Levine, Jennifer A. Mckinney, Eric Hoffmayer, Alistair D. M. Dove, Robert Hueter, Alessandro Ponzo, Gonzalo Araujo, Elson Aca, David David, Richard Rees, Alan Duncan, Christoph A. Rohner, Clare E. M. Prebble, Alex Hearn, David Acuna, Michael L. Berumen, Abraham Vázquez, Jonathan Green, Steffen S. Bach, Jennifer V. Schmidt, Stephen J. Beatty, David L. Morgan; Undersea Constellations: The Global Biology of an Endangered Marine Megavertebrate Further Informed through Citizen Science, BioScience, Volume 67, Issue 12, 1 December 2017, Pages 1029–1043, https://doi.org/10.1093/biosci/bix127
Hyperlink:
https://academic.oup.com/bioscience/article/67/12/1029/4641655
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