Sharks Win By A Nose: research details stereo olfactory ability

To be the efficient predators and scavengers that they are, sharks have an amazing array of sensory functions - from smell, sight, hearing/vibrations, to sensing electrical impulses. Working in coordination or in a sequence, these capabilities give sharks the edge to survive whether cruising an ocean reef or plying the wide open oceans hundreds of miles offshore.

Now, new research by the Woods Hole Oceanographic Institution (WHOI) and the University of South Florida shows how shark's sense of smell is even more refined than previously thought, by sniffing scents one nostril at a time - a sort of stereo smell-o-vision!

In a recent press release, WHOI researcher Jelle Atema said, “The structure of an odor plume is chaotic and not at all coherent. It’s just like what you see with the Gulf oil spill, which is essentially a gigantic odor plume. The plume breaks up into pieces, floats to different levels and gets transported in a current.”

By determining which nostril detects the odor first, the shark is able to determine a direction, much like our stereo hearing allows us to determine direction based on which ear detects a sound first or with greater intensity. The researchers confirmed this with tests using smooth dogfish, a small shark local to New England waters, and squid odor as an attractant.

But as Atema said, odors are transported rather haphazardly by currents, so sharks bring another sensory ability into play to help steer them in the right direction: the lateral line. This sensitive organ along a shark's body can detect faint vibrations in the water - vibrations like those given off by an injured fish or by the movement of water currents. Previous studies by Atema and fellow colleague Jayne Gardiner of the University of South Florida, showed that sharks use the lateral line to detect the direction of subtle currents - much like sensing wind on the hair of our bodies but with much, much greater sensitivity.

Combining these sensory abilities - stereo olfactory perception and lateral line vibrations - sharks are able to determine a direction and follow an odor to its source. “Inspired by odor, sharks also look for current,” Atema said. “The two together is what makes them so efficient.”

One more reason to look at sharks with awe and fascination and not ignorance or fear.

Read the Woods Hole press release.

Filmmaker's Journal: mackeral form massive aquatic highways

This past weekend, me and my good friend, photographer Budd Riker, went over to Catalina Island, off of Southern California, for a couple of dives. I needed to test out a new lens for my Amphibicam EX3 underwater housing - a great housing for a great video camera (the Sony PMW-EX3). I'm fortunate to have one of the few housings currently available in the U.S.

To make it quick and easy, Budd and I took the fast Catalina Express boat to the main island city of Avalon to dive at the popular Underwater Park at the city's famous Casino Point. With the park being a great place to conduct scuba diving classes, the sea wall at the point is typically lined with dive bags and assorted gear - and this day was no exception. It was crawling with divers.

But the Underwater Park seems to handle the diver pressure pretty well. It's a protected zone; you can't remove anything from the water except trash, no souvenir empty shells, no rocks, nothing. And because there is no fishing or hunting of any kind, it becomes a sort of refuge for many fish. Large calico bass will hang out in the flowing kelp and California sheephead will cruise by, seemingly aware that they are free from harm within the park's borders.

From above, we noticed that the visibility looked clear and promising, with a slight current moving through and bending the long stalks of kelp over to one side. Upon entering the water, our surface observation was confirmed: exceptional visibility for this location with an almost uncharacteristic blue tint to the water.

As we settled to the bottom, we were greeted by a large school of young mackeral. When they amass along the rocky shoreline, it's quite a sight to see. You have probably seen pictures or films of large schools of anchovies or other fish, congregating in immense balls. Well, for these mackeral, they instead form an undulating mass that weaves its way around the rocks and kelp like some elaborate network of aquatic highways with various underpasses, overpasses, turnoffs and junctions. Thousands of fish emulating California rush hour traffic (and when the current picks up, they come to a stop, hovering - just like our daily battle with gridlock!).

It's believed that a fish's lateral line - a sensory organ along the length of its body that can detect changes in water pressure - is what enables fish to maintain spacing and move en masse in schools. Each fish, when swimming, produces a pressure wave that the surrounding fish can sense and with that a collective sense of order and movement is established.

The mackeral continued to entertain us and gave us plenty of subject matter to film or photograph. They would double back, seeming to enjoy the security of the Underwater Park and only occasionally spreading out in large circles to give a possible hungry Calico Bass a wide berth, or darting about suddenly when a sea lion would make a quick pass.

Just an overall great day at one of Southern California's ocean treasures: a simple, little underwater oasis, able to withstand man's curiosity. Hopefully, with each new diver that completes their training at Catalina's Underwater Park, a conscientious ocean conservationist is born.

Video clips of schooling mackeral will be up soon in RTSea's stock footage library.