Thresher Shark Airborne: researcher takes remarkable pix of shark leaping

RTSea: With an elongated upper lobe of its caudal fin, the thresher shark is one of the most striking of all sharks. I guess that descriptor could be taken figuratively and literally as it has been shown that the thresher shark uses its tail to swat and stun its prey. Making the media rounds right now is a remarkable series of still photographs taken by marine researcher Scott Sheehan of a thresher shark leaping from the water in Jervis Bay, Australia. Possibly feeding on yellowtail baitfish, the shark leaped from the water and was first thought to be a dolphin. Sheehan readied his camera for a possible second leap and the shark did not disappoint, allowing the researcher to take a rapid series of shots. It is perhaps unusual behavior - or at least a rare occurrence - for a thresher shark to go airborne, but mako sharks have been seen taking large leaps and then, of course, there are the powerful images of great white sharks breaching as they

ambush seals from underneath. If you look at the complete series of photos, you can see the thresher sharks long tail curled - most likely snapping from side-to-side as it first breaks the surface; part of its powerful propelling motion as it moved through the bait fish. I have reported on thresher sharks before: about video taken showing one using its tail to hunt, highlighting ongoing behavioral research, and citing organizations working to help preserve this shark - listed as "vulnerable to extinction" by the IUCN. As Sheehan's images show, the thresher shark is a magnificent shark to behold whether in the water or in the air. It is also another important predator and member of a healthy marine community. Not a threat to man, it deserves our respect and protection.Source: RTSea

Read More........→June 09, 2012

Hawaiian Reef Sharks: possible competition for food causing massive decline

RTSea: For reef sharks, commercial shark fishing isn't the only thing that threatens their survival. In reef communities near populated islands, an additional threat comes from the taking of fish by local fishermen - fish that often constitute a major portion of the sharks' diets. When local and/or commercial fishermen compete for the same food source as reef shark species, it can be a crippling blow to the shark population. A recent study by Hawaii's Joint Institute for Marine and Atmospheric Research showed a drastic reduction in reef shark populations around populated islands in Hawaii as opposed to more uninhabited islands or pristine reefs. "We found 90-97 percent decline in reef shark abundance: white tip, grey, galapagos and nurse sharks," said Marc Nadon, a researcher with the Institute. The researchers have not been able to determine a more specific cause but look to accidental bycatch (sharks are now more protected, at least from legal commercial shark fishing, due to recent legislation) and overall fishing pressure as contributing factors. "70 percent of reef shark diet is reef fish, so if you remove the food source it would be logical that reef shark would follow the same trend and decline," said Nadon. While the researchers will be doing more studies this fall, their research's concern with competition for food has support based on what has been observed in other island nations. Both Samoa and the Marianas have seen major declines in reef shark populations around populated islands compared to other unspoiled reefs. Source: RTSea

Read More........→May 22, 2012