WaterNotes

Anyone else out there watch Discovery’s Deep Blue on this past weekend?  Were you as disappointed as I was?  Seems to be a major rehash of footage seen in the previously-awesome Blue Planet series.. down to the music.  And those segments that were new, had paltry little new information to share.  They hardly even identified the animals shown on screen.

Overall, E for effort and ennui. 

Still, there were some things that got me thinking.  A few clips included shots of whale sharks, one of my personal favorites.  We know so little about this largest extant species of fish.  

For instance, why do they have such vivid and beautiful spots on their bodies?  Other animals have somewhat similar camouflage to disrupt the outline of the bodies in the environment, and make them harder to see.  Predators like jaguars and leopards come to mind, as do the spot patterns on beautiful Hippocampus kuda seahorses, and the camouflaging forest floor mosaics found on fawns of white tailed deer.  Animals that need to hide from predators or sneak up on prey often have spots. 

The same goes for the counter-shading seen on these animals.. dark on top to blend in with the deep blue of the ocean from above, and light on the bottom to blend in with the lightness of the water column towards the sky when seen from below.  Its the same general contrast seen on dolphins, orca, and plenty of other piscivorous (yah, fish-eatin’) shark species. 

Given that these animals generally scoop and sift very small fish and plankton from the water, what would be the point in sneaking up on their prey?  And, better (and more intriguing), what does a whale shark need to hide from? 

Perhaps the answers aren’t as fantastic as I’d like.  Maybe a giant whale-shark-eating Nessie doesn’t lurk in the seas.  Afterall, for an animal that grows up to 20meters, they’re still born small.  Even the juvenile whale sharks wear spots.   Maybe the peculiar striations and spots resemble shimmerings line of light in their shallow tropical water habitat.  Other pelagic predators including marlin, oceanic white tip sharks, and blue sharks probably find a baby whale shark rather delicious. 

Perhaps mate selection answers the riddle entirely.  Maybe spots are sexy.  Maybe spots help signal reproductive fitness some how.  But maybe not.  We just don’t know yet.  We’re not even conclusively sure that these animals migrate after their planktonic meals. 

And consider this video of two juveniles ”playing” with divers and a film crew.  What sort of behavior does this video really capture?  Why would a 5meter whale shark juvenile swim up from the depths to investigate dolphin and seal-like animals at the relative surface? 

Did they think the divers were dolphins hunting and corraling fish?  Did they pinpoint the sound of exhaust bubbles in the water and arrive at the spot expecting the characteristic bait ball of fish and an easy meal? 

I think I love this part of science and fish and nature best.  The ability to ask questions that have no answers.. yet.