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Outdoors & Recreation
Dolphin Watch
What Porsches might say about populations
Article published on Wednesday, Nov. 28, 2012
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[Image]
Photo by ANN WEAVER
Calm water reflects a dock at dawn, symbolizing how the number of dolphins we see might reflect the number of dolphins weíre likely to see.
For the sake of argument, letís say that the bumper sticker, ďMy other car is a Porsche,Ē applies to me. In keeping with the fantasy, letís also say that my Porsche is painted Baltic Blue, the sweetest and sexiest car color that money can buy. Seeing the incomparable Baltic Blue on the unparalleled Carrera 4, countless drivers have called out sincerely, ďWhat a pretty car!Ē Little wonder that we call the car Baby.

I always park Baby by herself, as far away from other cars in parking lots as possible. This gesture is an obvious message to any clear-minded person, ďStay away! Ding some other car!Ē Despite this, I inevitably return to find that Baby has attracted a number of other parked cars, which then surround her.

I call this the decoy effect. Despite its message to stay away, a Porsche parked alone in its own corner of a parking lot attracts other cars the way an artificial duck decoy, floating in an empty pond, attracts live ducks flying overhead. Maybe people just canít help it; Baby IS enchanting.

But maybe the decoy effect isnít just for ducks.

The decoy effect is also what Porsches might say about populations, and specifically about the population of bottlenose dolphins around Johnís Pass.

Last week, Dolphin Watch reported that the number of dolphins using local waters has gone down 40 percent in the last eight years. There are several possible explanations, although if you love dolphins, why their numbers are down may not be as important as the fact that their numbers are currently down.

But I have to wonder if one possible explanation is something like the decoy effect, with other dolphins rather than ducks as the attractive bait.

Hearing is the primary sense in water and dolphins have fantastic hearing. They can hear other dolphins so much farther away than we can see or hear other people that itís hard to imagine that they can theoretically, and probably literally, hear all the other dolphins for miles around them.

What if these distant dolphins serve as decoys for other dolphins? What if dolphins used the number of the other dolphins they hear in a particular waterway, or the number of dolphins they donít hear, to judge the suitability of that area?

This wildly speculative but worthy thought puzzle would be a challenge to examine scientifically, but what if?

Just after Halloween, for example, Capt. John Heidemann and I were delighted to happen upon the sleepy trio of big bull N, his bull buddy Riptab, and young adult female Slightwin under the Tom Stuart Causeway. They appeared off our gunwale twice before ducking deep to swim out the other side of the causeway. As we waited for them to reappear, I realized with a shock that we hadnít seen N for five months Ė not since the start of summer, which is a gloomy example of the kind of behavior that creates the downturn in dolphin numbers.

We havenít seen Nís trio since. They didnít stay in the study area. What if groups like Nís trio listen for other dolphins as they cruise through our local waters and, based on what or rather who they hear, decide whether or not to stay?

We only found four other dolphins that day; did that low number have an anti-decoy effect and encourage Nís trio to keep moving, perhaps to other waters that other dolphins found attractive? Perhaps there is some critical number of dolphins that, like shoppers crowding one shop but avoiding another, influences others to stay or keep going.

One reason why dolphins might use the number of dolphins to judge a waterway is that theyíre intensely social. We see lone dolphins just 3 percent of the time who, with some exceptions, are usually swimming swiftly past on some important dolphin destination and are soon out of sight.

I canít tell you what criteria dolphins use to judge an area of water as suitable, but I can tell you that people have no clue what those criteria are.

There is a bay on our survey route, which will remain nameless, whose bottom topography, proportions of seagrass and sand, and icons on the fish finder appear no different to the human eye from the dozens of other bays on our survey route. But now that weíve surveyed it well over 900 times, I can say that the odds of finding dolphins there are small.

To emphasize the delight of data and ensure the accuracy of my claim, I created a stratified sample by inspecting every 10th survey out of the last 200 surveys to estimate how often and how many dolphins weíve seen in this perplexing bay. We only saw them their twice (a mere 10 percent of the time) and only saw seven dolphins.

The point is, is that people canít judge the adequacy of a waterway for wild dolphins; we can only take the dolphins word for it.

If my speculation about the decoy effect is right, dolphins may take each otherís word for it as well.

Dr. Weaver studies wild dolphins under federal permit 16299, National Oceanic and Atmospheric Administration. Send her an email at dazzled@tampabay.rr.com or visit her website www.dolphinsuperstore.com. NOAA advises anyone who sees a stranded dolphin in the Gulf of Mexico to call 877-942-5343 or 877-433-8299.
Article published on Wednesday, Nov. 28, 2012
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