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Dolphin Watch
Vital signs
By ANN WEAVER
Article published on Thursday, Feb. 8, 2007
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![[Image]](/content_images/020807_out-01.jpg) |
| Photo by ANN WEAVER |
| Researchers use physical markers such as the tatters that outline this dolphin’s dorsal fin for identification. |
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You see a person for the first time. You instantly decide how to act based on their gender and age, right? Gauged unconsciously, age and gender are vital signs for human interaction. And who hasn't recognized kinship from the similarities between siblings?
Consider dolphins. Most of us cannot look at one and know if it is young or old, male or female. We certainly can't see dolphin family ties, right?
We don't know the family ties among the bottlenose dolphins we study. We have yet to conduct the genetic studies that determine who is related to whom. Genetic analysis requires DNA.
There is DNA in every cell. To get DNA from dolphins, researchers use samples of skin collected by shooting each dolphin with a hollow point arrow, which yanks out a tiny plug of skin. It’s like taking a core sample from a tree.
Research suggests cetaceans do not mind such sampling. Yet, the huge humpback whales we sampled in Baja startled when the tiny biopsy arrow hit them.
Until we do our genetic studies then, we can only speculate about John’s Pass dolphin kinship from behavior.
This is the one-year anniversary of the last time we saw Stick's Mom. This adult female got her straightforward name the day her daughter Stick distinguished herself by playing a game of catch at sea (Catch with a wild dolphin).
Stick's Mom is or was one of my favorite dolphins; I don't know which. There's a chance we'll never see her again. There's a chance we will.
Some dolphins here leave this area for a year or more before returning. Stick's Mom is one of several adult females who frequented our area a couple of years ago and then disappeared. Whether they're just over the next maritime bend or gone permanently is unknown. Stick stayed here.
Months after our last observation of Stick's Mom, we were bouncing in the waves north of an island bird preserve when a dolphin suddenly shot by. Dashing and alone, it momentarily altered its torpedo course to veer by us without slowing. It shot out of sight.
You occasionally see such 'torpedoing' behavior here and elsewhere. You wonder if they're on a frantic search for other dolphins, racing towards unseen distant dolphins, or careening madly away from danger. Whichever, they're wholly preoccupied.
For an exhilarating moment, I thought it was Stick's Mom. It turned out to be Jagger. A relative newcomer, the tatters that outline Jagger's dorsal fin looks so much like Stick's Mom that it took careful comparison of hundreds of photo-identification pictures to determine that they're two different dolphins.
After Stick's Mom disappeared, we only saw Stick intermittently. At least 4 years old, she alternated between solitary stints in the area of her playful youth (The old neighborhood) and social stints in small riotous groups of other young adults elsewhere in the study area (Rain dance).
One morning last spring, Stick foraged alone off a small island. Mostly submerged, she searched an area the size of a football field. As she scanned for breakfast, the hydrophone tracked her streams of echolocation clicks between placid slaps of water and the various gulps and squeaks of other sea creatures.
Then she whistled. An answering whistle sounded in the distance. I said to assistant Marie Dahlberg, 'There's another dolphin on the other side of the island. Let's see who it is."
We drifted and listened. After more whistle exchanges, the second dolphin came out from behind the island. It was Jagger, heading straight for Stick. She stopped foraging and too approached directly. They met up, turned together and swam side-by-side for about 20 yards. Then they split up. Jagger continued north, leaving entirely. Stick resumed foraging.
Theorists propose that food and sex dictate mammalian travel patterns. Males travel in search of females; they remain with receptive females but otherwise continue their quest. Females travel in search of food. So Stick and Jagger's brief exchange may have merely reflected this central age-old behavior.
On the other hand, their brief interaction seemed so relaxed. It reminded me of the comfortability of good friends who fall easily into step and just as easily relinquish the contact.
Personally poignant was how their moment looked like Stick and Stick's Mom together once again. Science notwithstanding, I miss Stick's Mom.
The ease of their brief interaction was notable in a broader context: That was virtually the only time we've seen Stick and Jagger together though each spent the summer here. What vital signs obvious to the dolphins do we miss during observation? What if they're siblings?
Dr. Weaver studies wild dolphins under federal permit GA1088-1815, National Oceanic and Atmospheric Administration. Contact her at acweaver@tampabay.rr.com.
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Article published on Thursday, Feb. 8, 2007
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