Predator becomes prey

National Geographic Untamed Nature reports on an orca that was observed fighting with and overpowering a great white shark in “The Whale that Ate Jaws, http://tinyurl.com/2ffoep5.” Part of the program is posted at http://tinyurl.com/yc4n7vr. The fight was witnessed by a boat full of whale watchers, who captured it on video. Marine biologist Peter Pyle was working in the islands, and the boat captain contacted him. With a pole camera, he was able to capture underwater footage of two whales feeding on the shark. Marine biologist Mary Jane Schramm was on board the whale watching boat, the Superfish, and also witnessed the attack.

This relates to elephant seals because it happened in the Farallon Islands, where great white sharks gather to feed on elephant seals as they migrate north in the fall. Astonishingly, after this episode in 1997, all the sharks in the area, as many as 100 of them, disappeared from the Farallons, despite its importance as a feeding ground for them. A single elephant seal can be enough to keep a shark fed for three months. Four or five seals a year is a full diet for them. The sharks stayed away for the entire feeding season.

The program speculates that chemicals from the dying shark were released into the water, and that’s what drove the sharks away. That didn’t sound like a complete explanation to me. If that were enough to protect sharks from being killed, why doesn’t it keep them away from the nets of fishermen who take sharks for their fins, and throw the dying fish back into the water?

Additional videos are posted at http://www.youtube.com/watch?v=W8GaDuCvYbE and http://www.youtube.com/watch?v=xcsSSxNuUiI. Both come from California.