Ridges and grooves

Here's a fun set of mystery close-ups for you.

 

All of these images were taken under a microscope.  (There are some sand grains in the pictures, too.  For example, the amber-colored grains above.)

 

All of the pictures are from the same animal, just from different parts of the body.

 

Here's one more close-up, and then the next picture following this one will give the answer away, so consider yourself warned!

 

Okay, here we go.  Are you ready?  Do you have a guess?

 

All of the close-ups were the scales of a shark, probably a juvenile Salmon Shark (Lamna ditropis).  You can see some of the scales directly below the teeth in the image above.  I just found out about this shark at the end of the day, so I'm not sure I heard all of the details right...but it sounds like Matt and the Coastal Oceanography class discovered it on Salmon Creek Beach.

When I looked at the shark's skin with my hand lens I was so impressed with the scales that I couldn't resist taking a few pictures under the microscope to share with you (the shark was very small).  Note that some of the scales have very obvious longitudinal ridges.  It's thought that these ridges and grooves (running parallel to the water flow) reduce drag and thereby improve swimming performance.

This shark was in poor condition — it had probably been on the beach for a while and was partly scavenged and severely dried (next image).  But I've heard about a few other recent Salmon Shark strandings, so it's an opportunity to provide a little information about these events.

 

 [For scale, this shark was only ~2 feet long.]

For at least 20 years, juvenile Salmon Sharks have stranded on California and Oregon beaches in the late summer and early fall.  Until recently, the cause was unknown.  But last year, several researchers published a paper in which they discovered that stranded sharks had bacterial brain infections.  (It still isn't clear how or where the sharks acquire the bacteria.)

Schaffer, P.A., B. Lifland, S. Van Sommeran, D.R. Casper, and C.R. Davis. 2013. Meningoencephalitis associated with Carnobacterium maltaromaticum-like bacteria in stranded juvenile Salmon Sharks (Lamna ditropis). Veterinary Pathology 50: 412–417.

If you'd like to learn more general information about Salmon Sharks, check out the web pages provided by the Pelagic Shark Research Foundation and the Florida Museum of Natural History.