Dive Time with Tim Grollimund

Stingrays offer new design opportunities

November 21, 2013 

A stingray forages on the sandy bottom with a group of hogfish. (Photos by Tim Grollimund)

Stingrays always invite me to stop. They usually don’t mind a short visit.

You can tell when they have had enough — a small movement of a wing means “you are in my space,” and they usually settle back into the sand when you back off a bit.

Just like people, they have personalities. Some are shy, and some I can get so close I have to back away to get them in the frame. It’s always a productive day when I can process some stingray shots in the evening to send to my dive buddy for his ScubaBoard trip reports.

Recently, I read a little bit about the sea life on the sand bottom, and I am setting up an interview with a scientist to learn more. I thought it might be nice to know a bit more about the animals that call sand their home, since I don’t really think about it all that much.

I thought I’d begin with the most obvious sand bottom predator, the stingray. Seeing a stingray is usually a highlight of a dive. I don’t know if it’s their size or their graceful motion that tops the “I-saw-that” chart, but I sure get a kick out of seeing them, and always will. Maybe it’s the seemingly effortless flight, or the eyes poking out from the sand when they are buried. Their swimming motion is unique. More on that in a minute.

In 1988, when it was only a few years old as a major tourist site, I did the Stingray City thing on Grand Cayman. We sure had a blast, and I have some very nice images from that experience. It’s one of the things you have to do if you go to Grand Cayman — like the roller coasters at a theme park. You have to take that ride to make the trip complete.

The value to the local economy is huge. The Guy Harvey Research Institute estimates the annual value of a stingray at $500,000, and its lifetime value at $10 million. As always, there is a downside to the interactive attraction. Studies show significantly altered behavior — from night to day, literally — from the continuous interaction over the years. See a couple of articles on the Cayman stingrays here: http://guyharveysportswear.com/blog/tag/stingray/ and here: http://www.newswise.com/articles/tourist-fed-stingrays-change-their-ways

This makes me wonder if our stingrays and other charismatic mega fauna are even more valuable, since (Robbie’s and Captain Slate’s creature feature aside) we don’t feed animals on a recurring bases here. Is the wild encounter worth more to visitors than the staged encounter? I don’t know the answer to that.

The staged encounter is certainly easier to measure economically, since random wild encounters are embedded in the overall trip value and cannot necessarily be segmented as a specific event. I love the photo opportunities of a staged event, but I am a bit more thrilled when I encounter a charismatic animal in the wild, like the reef shark I wrote about recently. Even better than that, how about the value of seeing a manta ray, or a whale shark — and what is the value for the guy that captured the video of the great white shark on the Duane this summer? Priceless.

One of the most significant developments of Cayman stingray studies is a model by Christina Semeniuk that provides a framework to explore the long-term viability of wildlife tourism attractions. It’s the chicken and egg scenario applied to the reef.

The attraction is dependent on both tourism and wildlife. Their model seeks to find the optimal wildlife sustainability point and maximize the tourist scenario simultaneously. It’s not an either/or equation for them. The model projects the effects of proposed management scenarios on the wildlife and tourism sectors together rather than each sector, or species, individually. This is a very interesting concept, and one I believe could have implications for our region. You can download the paper here: http://timgimages.com/PDF/SemeniukEcoModel.pdf

The unique swimming motion I mentioned earlier is the subject of a new study by engineers at the University of Buffalo. Richard Bottom and Iman Borazjani are using fluid dynamics to chart the flow of water around the stingray’s swimming movements. What they will present later this month at a fluid dynamics convention is a first look at their study of the leading edge vortex in an underwater context. It has been described in birds and insects, but not in an aquatic setting.

A ray’s unique motion causes lower pressure in the front edge, and higher pressure in the back, essentially pushing the ray through the water. Perhaps that’s why it looks effortless to us. They want to enhance the efficiency for cars, planes and submarines by applying these dynamics in new designs. Seehttp://www.buffalo.edu/news/releases/2013/11/013.html

Male stingrays are sexually mature at a much smaller size than females (20 inch wingspread compared to 29 inch width for females). Males also change the shape of their teeth during the mating season, from molars to sharper, pointed teeth for gripping the female. To deal with the chomping of the males, females have skin that is 50 percent thicker than a male’s skin. Brings a whole new meaning to the phrase “grab it and go,” doesn’t it?

You can see a photo of the mating season teeth here: http://www.science.fau.edu/sharklab/pages/stingray_mating_res.html In the weird creature a category, there is a freshwater stingray in Asia that grows up to 16 feet wide, and can weigh up to 1,300 pounds. You really need to take a look at this one: http://www.wired.com/wiredscience/2013/09/absurd-creature-of-the-week-giant-stingray/

Tim Grollimund is a freelance photographer and PADI divemaster based in Key Largo. He can be reached at tim@timgimages.com or through his web site atwww.timgimages.com.

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