Tuesday, August 12, 2014

Move Over Megalodon - Actual Sharks Are Far More Interesting!

In honor of Shark Week, let's examine some recent shark research.  But unlike shark week documentaries, I won't lie to you (no, Megalodon is not still living). 

Sharks are friggin' amazing works of evolution!

This is a shark egg! Although
many shark species have
live births.
I've always found sharks super interesting, and would have loved to study sharks if I had gone into an animal-related field.  While many people are terrified of sharks, I have lived in awe of how amazingly adept they have been at surviving and thriving over the last 420 million years.  Seriously, sharks are some of the oldest vertebrates on the planet!  They have rows of teeth that form inside a groove and gradually move forward, like a conveyor belt - because sharks lose, on average, 30 000 teeth in their 20-30 years of life. 

Other cool non-dental shark facts:
  • Because their skeletons are more cartilage than bone, and therefore less dense, sharks do not need a swim bladder for buoyancy.
  • They lack a rib cage, and are easily crushed by their own weight on land.
  • Sharks have got fluid dynamics down!  They are not only shaped like bullets, but they are covered in dermal denticles (translation: skin teeth) that reduce drag and turbulence while swimming.
  • Shark blood has high concentrations of urea and trimethylamine N-oxide, which keeps it in osmotic balance with seawater, confining sharks to marine environments.  See, you'd never find a shark in one of the Great Lakes (Shark Week, shame!). 
  • They have brain-to-body ratios similar to those of mammals and birds, and have shown signs of curiosity and playing, making them intelligent creatures.
  • On top of having an enviable sense of smell, sharks also use electroreception to find prey and orient themselves with the Earth's magnetic field! 

Only three of the 470 species of sharks are dangerous to humans (the great white, tiger, and bull).  According to the International Shark Attack Files, there have been 2667 shark attacks in the last 433 years, coming to an average of 6.2 attacks per year.  You are more likely to be struck by lightening or bitten by another person than you are to be attacked by a shark.

Alright, now that we've gotten that out of the way, let's move on to some recent shark research. 

100 million years of evolution has made the hammerhead shark vulnerable.  You'd think that after that much time evolving, sharks would be unstoppable, indestructible killing machines.  But you'd be wrong.  Hammerhead sharks are extremely vulnerable to human-induced stressors, like overfishing and polluting the oceans.  Hammerhead sharks owe their distinctive head shape to their improved eyesight, which was also accompanied by a change in brain size and complexity - they have larger brain-to-body ratios than other sharks, with regions involved in social intelligence and other cognitive abilities being enlarged.

This also came with an enhanced sensory system, including electroreception.  Hammerhead sharks are able to detect electric fields from greater distances away than other shark species.  But this adaptation never had them distinguish between prey and fisheries.  The electrical fields from the fishing industry attracts hammerheads more than other species.  As such, hammerhead sharks are also more sensitive to the stresses of catch-and-release fishing than other shark species, with increased mortality as a result of contact with the fisheries industry.  This is really important to keep in mind for conservation efforts, because some researchers are starting to suggest that catch-and-release methods are the most humane way to keep swimmers safe from sharks.  While it may be better than killing them on site, only about 74% of bull sharks and 53% of hammerheads survived in the 4 weeks following the catch-and-release study.

Citizen science is just as effective as experienced monitoring.  That's right, shark counts collected by divers is consistent with shark counts conducted using tagging and acoustic telemetry by researchers and conservationists.  See, science and animal conservation is for everyone!

While many species of sharks remain on the list of endangered animals, a lot of great progress is being made in the regulation of fishing and shark killing.  The Smithsonian Ocean Portal has a great video showing the growth in regulations in the last 35 years.  You can watch it here.

On a side note, I find it incredibly sad and insulting that Shark Week feels the need to sensationalize and lie to get people excited about sharks.  Seriously, take a trip to Wikipedia and then tell me you think sharks are boring.  Maybe Shark Week should have more faith in the intelligence of its audience?

Anyway, happy Shark Week everyone!

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