When animals don’t behave

Last December, I sailed to the Lakshadweeep with a headful of island dreams. I was to study the foraging behavior of green turtles in the shallow lagoons of the Lakshadweep islands, where this lone herbivore among marine turtles feeds on seagrass beds. I wanted to understand drivers of green turtle movements within island lagoons, and believed it was mainly the distribution of foraging resources. Kartik and I hoped that this preliminary study would give us clues to understanding larger inter-island movements that were reported by Rohan and Nachiket in their previous work in the Lakshadweep. I knew from studies in other locations that green turtles were permissive to behavioural observations in places such as the Hawaii islands. Given this, a part of my planned work was to identify green turtles individually and follow them to collect behavioural data. Meanwhile, I also spun a million dreams of swimming with greens in turquoise blue lagoon waters, quite apart from scientific objectivity. What I expected to record was something like this.

Green turtles are no dolphins. Because when I eventually did snorkel in the Kadmat lagoon, the turtles did a Sonic the Hedgehog on me. All I saw were sand plumes left behind by fleeing turtles, even before I could spot them in the lagoon. Interestingly, unlike several other places around the world where green turtles are found, they seem to be especially skittish to approach by snorkelers in the Lakshadweep. And the pattern differs between islands and island zones, seemingly based on boat traffic. Green turtles show more spunk near jetties, and in islands where human activity is relatively high – closer to the shore and in islands like Agatti which boasts of several tuna boats. Also, on our dives near the reef, green turtles were quite unwary of divers in the water column. They would swim past us slowly – droopy-eyed, with a stoned look on their faces (which makes me wonder, do turtles get narced?)

Since sand plumes don’t make good data, I decided to shift strategies. With a lot of help from Teresa, a seagrass biologist from Barcelona, I designed cafeteria experiments to study feeding choices in green turtles. I pitched my seagrass plots in the Kadmat lagoon, duck diving till I got breathless, and waited to see signs of turtle herbivory. But nothing happened for several days. Once in a while a stray fish nibbled on the leaves, but the turtles didn’t bother. One evening after setting up yet another pair of plots, I sat by the resort steps waiting to see if I had got the location wrong, if there were any turtles there at all. Even before a minute was up, I saw them pop up one after another right around the spot where the seagrass plots were. But strangely, they just wouldn’t feed. And to my annoyance they sounded like they were blowing raspberries at me when they surfaced, mocking at my predicament. After many attempts I  eventually gave up plans of behavioural observations, and dejected, set to finish the rest of the work I had planned.

However, I did not leave the islands without realizing my dream. It was a fateful February afternoon when Kartik and I met Patrick. Pat (also known as ‘Hol(e)y’), is a big male green turtle which hangs about in the only strip of seagrass left in Kavaratti, adjoining the Sandy Beach coffee shop. It was wonderful following Pat around the lagoon, as it glided slowly through filtered beams of sunlight cutting across the water column, surfacing once in a while. His long tail kept curling and uncurling as he swam, as if asking me to follow. Kartik and I swam with him for a long while and then moved to where Anne was following her mixed species shoals of fish, which were putting up quite a show. After the day’s work, we sat drinking cups of coffee at Sandy Beach looking at the pictures we’d just taken. I asked Kartik about the curling of Pat’s tail which I had noticed in some of the pictures, wondering if it had any behavioural significance. Kartik jokingly said that male green turtles were known to quite indiscriminately mount any moving object that they saw. Maybe it was beckoning me to join him – Anne said, and we all had a good laugh.

I’d forgotten about the incident until much later once I got back to Bangalore, when I came across this.

Kartik was not joking after all. :^/

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2 comments

  1. Naveen Namboothri

    Hey Bharti,
    Nice one… :).
    About the turtles getting narced… I think there may be a point there… 🙂
    I have seen monitor lizards that are usually wary of people, getting sluggish and chilled out in shallow waters even when you get within a few inches of it… I feel the lower seawater temperatures and consequent reduction of metabolic rates could be a possible explanation? Maybe (as you put it) ?stoned” would be a better expression to describe this behaviour….
    Naveen.

    • bhartidk

      Lowered metabolic rates/high energetic costs of shifting depths might be the reason behind their lack of fear as you suggest.

      Also, you might find this interesting: http://jeb.biologists.org/content/213/23/4074.full.pdf
      They talk about adaptations in leatherback turtles which enable them to dive up to several hundred meters(!!!). Apparently having a leathery flexible carapace, large oxygen stores in their blood, greater blood nitrogen solubility compared to endothermic mammals and opting for slow ascent at smaller angles are the key players. Marine turtles in general seem to be less susceptible to nitrogen narcosis and decompression sickness.

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