Wednesday, April 27, 2011

Sparkle-Clean Sharks: thresher sharks practice good hygiene in the Philippines

As marine biologists continue to study the physiology and behaviors of sharks, we are learning more and more about these fascinating creatures and what we can do to protect them if it's not too late. Case in point:

Thresher sharks have been greatly depleted in number - caught for their fins and meat - which is disappointing over and above the obvious loss in population because it is a very unique species. The thresher shark's namesake elongated tail fin has been shown to be used as a hunting tool, slashing and stunning its prey. Diver encounters with thresher sharks have always been scarce as they often swim in deep, open waters and don't typically congregate in large groups.

However, off the northern tip of Cebu in the Philippines, a dive tourism business is growing based on the thresher shark. Apparently, a concentration of thresher sharks frequent a seamount there, which increases the opportunity for divers to see these beautiful sharks in the wild.

Researchers from U.K.'s Bangor University have been studying the behavior of these sharks in the Philippines and have recently published their findings in the journal PLoS One. According to the research team, the thresher sharks are frequenting the deep seamount to get a good
cleaning. Residing at the seamount are a number of cleaner wrasses, a fish well-known for cleaning larger reef fish by picking away parasites and dead skin or scales. It seems that thresher sharks have caught on to the benefits of this hygienic service and will cruise close to the seamount, slowing down to half their normal speed and allowing the cleaner wrasses to give them a thorough once over.

The researchers have filmed this behavior, amassing over 1,000 hours of footage. They are quick to point out that mankind can have a disruptive effect on this symbiotic relationship - the seamount already shows evidence of dynamite fishing, a local commercial technique that literally destroys reef communities.

According to lead researcher Simon Oliver,
“Our findings underscore the importance of protecting areas like seamounts which play an important part in [the sharks'] life strategy to maintain health and hygiene.”

Fellow researcher Dr. John Turner said, regarding their studies, “The work uniquely describes why some oceanic sharks come into coastal waters to perform an important life function which is easily disturbed by man.”

No comments: