Sharks play an essential rol in the health of our oceans

Information, News, Research

It’s in your eyes!

A  shark has different eyes than a human: they are on different sides of the head, creating a 360-degree field of vision, with two blind spots in front of the snout and right behind the head. Sharks have limited vision, only able to see 15 meters ahead, so sight is only important when close to the prey. Like humans, sharks have a lens, a retina, an iris and a cornea.

 

One very important feature of shark sight is the tapetum lucidum, made up of mirrored crystals, which is how sharks are able to see in the low light created by murky or deep waters­. Like cats, sharks’eyes can glow in the dark.  TIn a shark, though, the tapetum lucidum is about two times as effective at reflecting light as it is in cats [source:  Seaworld]. Because of the tapetum lucidum, a shark can see about 10 times better than a human can in dim light, like during dusk or dawn, their natural time to hunt.

 

Eye of shy shark (picture: Peter Verhoog, Dutch Shark Society)

Now, shark and other fish eye lenses are used in research. They have the potential to serve as a chronological record of biochemical information, allowing examination of ontogenetic movement patterns, migration and juvenile ecology (ontogenetic: of or relating to the origin and development of individual organisms; “ontogenetic development – we had to look it up too!)

Katie Quaeck of the University of Southamption, UK has studied the dietary ecology and movement/migration of the Porbeagle shark (Lamna nasus) using stable isotope analyses from sequential samples of eye lens tissue. Read more about her fascinating research at:

http://www.southampton.ac.uk/oes/research/projects/shark_and_other_fish_eye_lenses.page?

 

Dissection of a shark eye shows the reflective layer (tapetum lucidum) that increases the sensitivity of the eye in low light conditions, plus the lens lying outside the eye. Picture: A question of balance, Aqob.com.au

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