Bite into research: Genetic diversity and connectivity of the megamouth shark

The Fins United Initiative is excited to showcase a BRAND NEW section to our program: the "Bite into Research" segment! TFUI officers will be reading articles that were published in regards to Chondrichthyans (those are the sharks, skates, rays, and chimaeras... and include any sector) and explain it in terms that everyone can understand. Today, we have TFUI Officer Chelsea Stein reviewing the following paper: Genetic diversity and connectivity of the megamouth shark.

​What did the researchers do?
Have you heard of the megamouth shark (Megachasma pelagios)?  It’s one of the more bizarre-looking sharks that rarely has the spotlight in news, movies, and even science.  The first megamouth shark wasn’t caught until 1976 and then officially declared as its own species in 1983.  If you consider the fact that most modern sharks emerged during the Jurassic Period (about 200 million years ago), and humans began researching sharks in the 1800s, the megamouth shark seems all the more new and mysterious. 
 
As noted in this article, only 100 megamouth shark specimens have ever been caught or recorded.  However, these sharks have been found in widely distributed areas like the Indian, Pacific and Atlantic Oceans.  Satellite tagging has not been used to study the megamouth due to the sharks’ “scarcity and vulnerability.”  So there is little data about the shark in terms of its diversity, movement, and behavior.
 
The researchers in this study worked to better understand megamouth diversity and connectivity from specimens found across the globe.
 
How did they do it?
The researchers used tissue samples collected from Mexico and Taiwan, along with gene sequences collected in previous studies from Japan, Puerto Rico, and Indonesia.
 
What did they find?
 
A majority of the DNA were found to be identical.  There were no genetic structures identified and no difference from one region to another.  So, the megamouth shark could likely have small populations that swim very long distances, across the world’s oceans. 
 
Other shark species that have been found to swim long, ocean-wide distances include basking sharks, whale sharks and blue sharks.  They are referred to as pelagic sharks.
 
You might be thinking this isn’t shocking to find that a shark is likely swimming across the ocean.  But not all shark species swim such far-reaching distances.  In fact some sharks have been found to have fairly consistent movement patterns in specific geographic areas.  These sharks, including blacktip sharks, sandbar sharks and even tiger sharks, are often found to have higher diversity and swim near coastal areas.
 
Another finding from the study for you to bite into: all of the specimens from Taiwan were found to have the same content within their stomachs; they are exclusively feeding on krill.  The researchers think that the megamouth sharks are likely traveling to the Northern Pacific to feed when the krill is most abundant each year.
 
Due to the small sample size and other limitations on the DNA variety, more research is needed to fully understand the behavior and diversity of megamouth sharks.
 
Why does it matter to people?
People have only considered the megamouth to be a species for the past 36 years.  At this point, we need to be collecting as much data as we can on the megamouth just to understand it.  This study is important because it provides a brief look at this unique species and lays the groundwork for further awareness and understanding.
 
How does it help Chondrichthyans?
The megamouth is currently listed as “least concern” on the International Union for Conservation of Nature (IUCN), which categorizes a species’ risk of extinction.  As explained in this study, “genetic diversity is one of the important indexes to be considered in shark management and conservation policies because the long-term survival of a species is strongly dependent on the levels of genetic diversity within and between populations.”
 
Pelagic sharks, known for their lower diversity and ocean-wide movements, require distinct conservation policies.  Accurate data, specifically to understand megamouth diversity, will inform such conservation lists and allow decision-makers to more precisely protect the species.

GUEST BLOGGER AND TFUI OFFICER CHELSEA STEIN

​Chelsea (aka "Chelsie") Stein loves the great white shark and epaulette sharks. She is currently located in Michigan, USA and is available for in-person and Skype classroom visits!