Dive Dry with Dr. Bill

#425: Dinner Delicacies... Off Menu

I usually don't write about other regions of the world and their species unless I've actually been there and filmed the critters myself. However, through my contacts on the Internet, I often "encounter" stories in cyberspace that I feel are worth sharing with my readers. One written by Ben Raines of the Mobile (AL) Press-Register was forwarded to me by Kurt Lieber of Ocean Defenders Alliance. The article talks about recent findings from research on tiger sharks by scientists at the Dauphin Island Sea Lab in Alabama.

Now sightings of tiger sharks are extremely rare in Catalina waters. The only one I'm aware of was by divers from CIMI who reportedly saw two juveniles at Hen Rock some years ago. My only experience with these fish occurred back in the early 1970s when I was collecting specimens for the Los Angeles County Museum of Natural History in the region of the midriff islands in the Sea of Cortez. My lab assistant, Barry Aires, and I were paddling our kayak out from our campsite near Kino Bay to Pelican Island, about 5 miles away.

We were three miles offshore when I detected something approaching from the port side in my peripheral vision. I looked over and there was the dorsal fin of a very large shark approaching. The head surfaced and turned so the large dark eye stared directly at me. I quickly raised my paddle and braced for the impact. What we gauged to be a 22 ft tiger shark (exceeding the world record at the time) bumped the bow of our kayak where I was seated, passed underneath the boat and disappeared. Barry and I were sure it would return and we would be goners... but it didn't, as you can tell since I'm writing this tale. We paddled out to the island and were too scared to return until well after dark, guided to our site by a Coleman lantern left on the beach. When we walked into the small town, the local shrimp fishermen in the corrugated tin restaurant had seen us out there and thought we were "the bravest men in the Sea of Cortez." since we had survived the incident. They told us several of their crew members had slipped off the decks of the shrimp boats only to be eaten by "El Grande Tuburon."

I think the tiger must have decided the rubberized skin of the 18 ft Klepper Fol-boat we were in just wasn't very palatable, despite their reputation of eating anything. Speaking of which, I'd better get back to the article before you all doze off! Scientist Marcus Dryman had dissected several tiger sharks from the Gulf of Mexico, and found balls of feathers in their stomachs which he compared to the hair balls in cats. But the feathers weren't from pelicans, seagulls or other marine birds. They were from woodland birds known only from forested terrestrial habitats! Three species that were identified included the yellow-bellied sapsucker (a form of woodpecker), the brown thrasher and a scarlet tanager.

So how does a tiger shark encounter a woodland bird far out at sea? The scientists came up with an interesting theory. Each of these birds is known to migrate seasonally across the Gulf of Mexico, and Dauphin Island is at the center of one of the largest migratory bird corridors on our continent. The scientists discovered a federal study from 2005 that described how migrating birds would become confused at night when they encountered the bright lights of oil and natural gas platforms out in the Gulf. Migratory bird species including hummingbirds, doves, falcons and others were documented circling these platforms in numbers estimated to exceed 100,000 at a time.

The birds often flew around the platforms for several hours, with some becoming exhausted and falling into the sea to die. After flying nearly 800 miles without much food, they might not have had the energy to arrive on land after the merry-go-round detour. Once the wings of these terrestrial species hit water, they would have little chance of taking flight again. Since tiger sharks will eat almost anything (except a rubberized canvas kayak), they snap up these exotic delicacies, apparently appreciating a treat "off menu." Scientists Dryman and his teammate Sean Powers acknowledge that this is an hypothesis and needs further review and testing before the theory will gain wide acceptance. I recently read that light bulbs giving off mostly green wavelengths do not attract the birds and are now required on rigs in the North Sea by the European Union.

After reading this, I'm happy that the tiger shark we encountered down in the Sea of Cortez had a more discriminating palate than some of its relatives. I should add that when we were greeted by the shrimp fishermen after our ordeal, we were their honored guests that evening. They gave us all the food we could eat and beer we could drink. However, I must acknowledge that I was even more discriminating than the shark in what I ate that night. When my spoon brought up a jawbone or eyeball from the fish soup, I discretely hid it from my dinner hosts!

© 2011 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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A rather confused yellow-bellied sapsucker wondering just how it ended up in the jaws of a tiger... shark!

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