Monday, 15 May 2017

3 Dead, Liverless Sharks Wash Ashore in Weird Whodunit

By Laura Geggel, Senior Writer | May 11, 2017 06:58am ET 

In a strange case of extremely picky eating, orcas off the coast of South Africa are killing great white sharks, but the killer whales are chowing down only on the sharks' livers and, in some cases, their hearts, researchers say.

In a four-day period starting May 3, researchers found the bodies of three great white sharks (Carcharodon carcharias) that had washed ashore along South Africa's Western Cape province. Saddened and mystified by the deaths, the researchers performed necropsies (animal autopsies) on all three.

No one saw the sharks' last moments, but their injuries indicate that orcas, also known as killer whales (Orcinus orca), were the culprits, the researchers said. 

"These observations are unprecedented," Alison Towner, a white-shark biologist for the Dyer Island Conservation Trust in South Africa, wrote on the Marine Dynamics blog, a site hosted by a shark cage diving company. "We don't really know how long the sharks will stay away from the area as a result of predation pressure."

Although orcas aren't known to regularly hunt great white sharks, "it's not unprecedented," said Andrew Nosal, an assistant professor of biological sciences at Saint Katherine College in San Marcos, California, and a visiting assistant researcher at Scripps Institution of Oceanography in San Diego. (Nosal was not involved in the recent shark analyses.)

Scientists know that both orcas and great whites live off the western coast of South Africa, where the Atlantic and Pacific oceans meet. Although Nosal wasn't aware of orca-on-shark attacks in that area, he had heard of instances in which orcas have hunted the sharks in other locations, such as off the coast of southern Australia and near the Farallon Islands, a wildlife refuge off the coast of San Francisco, he said.

In addition, orcas are known to hunt and eat the livers of the broadnose sevengill shark (Notorynchus cepedianus) off the coast of California, said Chris Lowe, director of The Shark Lab at California State University, Long Beach, who wasn't involved with the South African analyses.

Not much is known about orca predation on great white sharks, Nosal said. But any marine biologist can tell you that other marine mammals prey on the livers and internal organs of smaller sharks, he said.

For instance, sea lions routinely hunt leopard sharks off the coast of California. In grisly detail, Nosal described how sea lions grab onto leopard sharks (Triakis semifasciata), and then twist and turn the shark until they can bite just under its gills.

No comments:

Post a Comment

You only need to enter your comment once! Comments will appear once they have been moderated. This is so as to stop the would-be comedian who has been spamming the comments here with inane and often offensive remarks. You know who you are!

Related Posts with Thumbnails