Looking glass into the secret lives of whale sharks

Written by on March 16, 2016 in Marine Life, Sharks

By Bridget Altman

A snorkeler swimming with a 6 meter long whale shark.

A snorkeler swimming with a 6 meter long whale shark. Photo credit: FGBNMS, NOAA.

There are very few places in the world where you can swim with manta rays, hammerhead sharks, sea turtles, and whale sharks in the same dive. Darwin Island in the Galapagos is one of these special places. Areas like this serve as rays of hope in a sea where many populations of our large species (megafauna) are rapidly declining. They are also important areas for scientists to study.

Marine biologist and photographer Dr. Simon J. Pierce is the principal scientist for the Marine Megafauna Foundation. This world-renowned expert on whale sharks (Rhincodon typus) first visited Darwin Island in 2014. He seeks to solve what he calls “the Great Whale Shark Mystery.” Pierce joined forces with the Galapagos Whale Shark Project’s Dr. Jonathan Green and Dr. Alex Hearn to get some answers and game-changing photographs.

The need for more answers is exactly why Pierce went back to Darwin Island in September 2015. Darwin Island is a looking glass into the secret lives of whale sharks. It is one of few sites where pregnant females regularly reside from July to December, coinciding with plankton blooms. Armed with satellite tags and his favorite tool, a camera, Pierce set out on a dive to track these plankton-eating sharks. Satellite tags are amazing scientific tools to monitor the movement patterns of these gentle giants. However, they are also very costly. A cheaper alternative is photography; photographs are a non-invasive tool that can be used to identify and track these sharks over long time periods.

Whale sharks have a global distribution. However, they tend to congregate in certain hot spots for a season and then disappear. Reasons for this “disappearance” are parts of the mystery Pierce and his colleagues hope to solve. There is a famous saying among fish biologists, “Studying fish is like studying trees, except they move around and they are invisible.” Whale sharks are no exception to this rule.

To keep better track of these elusive animals, conservation organizations like ECOCEAN took inspiration from NASA in order to build a Whale Shark Identification Database. Utilizing the Groth Algorithm, a computer-based formula initially used by astronomers to map star patterns, marine biologists can use the shark’s unique spot pattern like a fingerprint to determine if, when or where that shark has been documented previously. This creates a record of the sharks, which can ultimately help to answer vital questions about migration and life history.

ECOCEAN whale shark identification method.

ECOCEAN whale shark identification method.

By simply capturing a photo of the area near the 5th gill slit and pectoral fin on the left side of the shark, divers and scientists alike can add to the database; citizen science at its finest! Approximately 7000 individual sharks have been individually identified by their unique spot patterns. Pierce reports that about 70% of these are juvenile males. Reasons for this gender disparity, where these sharks mate, and where they give birth remain part of the “Whale Shark Mystery” that Pierce hopes to solve.

To date, there has only ever been one pregnant female whale shark specimen examined by scientists. It was caught by a fisherman in 1995 near Taiwan. Scientists discovered 304 embryos in her uterus, ranging from embryos in egg cases 16 inches (42-centimeters) long to 2-foot long (64-centimeters) embryos without egg cases, living freely in the womb.

Everything we know about the reproductive history of Whale Sharks we know from this one representative specimen. Considering this specimen was relatively small for a whale shark, at 10.6 meters total length (34.8 feet), some members of the whale shark biology community believe a whale shark can carry even more than 304 embryos at a time. It is well documented that the amount of embryos a fish can support increases exponentially with abdominal size. The largest whale shark on record was reportedly 20 meters in length (65.6 feet); a shark of that size has the potential for a very large abdomen and A LOT of embryos.

On one dive in 2015, Pierce snapped this amazing photo showing a pregnant female. If you look closely you can actually see the shape of her embryos! Documenting this pregnant female means that we are one step closer to an answer for these questions. They say a picture is worth a thousand words, and in this case, it could also be a scientific breakthrough!

Pregnant whale shark. Photo courtesy of Dr. Simon J. Pierce.

Pregnant whale shark. Photo courtesy of Dr. Simon J. Pierce.

Be sure to check out Simon J Pierce’s website to see his photography and blog posts about his travels and research!

YOU can help solve the “great Whale Shark mystery” by adding your photos to the Whale Shark identification database.


 

Bridget Altman is a graduate student at Scripps Institution of Oceanography studying Marine Biodiversity and Conservation. She hopes to help the world understand the importance of ocean stewardship. She has a passion for all ocean creatures, specifically apex predators. She ultimately wants to become a PR agent for sharks.

Copyright © 2016 by Marine Science Today, a publication of Marine Science Today LLC.

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