Final Diamondback Terrapin Blog

After eight weeks of lab and field work my summer research has come to an end.  While it’s nice to be back home where I can relax and sleep in, I really miss the terrapins!

All in all we caught 51 individual terrapins.  12 of those were female, and 39 were male.  Ages ranged from 3 years old to older than 8 (after a certain point it’s not possible to determine the age because the ridges on their shells start to wear down).   We also had 47 recaptures, including one terrapin that swam into the traps 4 times.

By the end of the sampling period, I was able to recognize a few of the terrapins based on differences in size, shell color, and the pattern of spots on their skin.  Some had very dark, almost blue or black shells.  Others were a lighter green or were almost completely covered in algae.  And some had many, small spots on their skin while others had fewer, larger patches of dark color.

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We also caught some other organisms in our traps, including crabs, fish, and jellyfish.  The presence of these did not seem to interfere with catching terrapins in the traps, and it was fairly easy to turn the trap upside down empty them back into the water without touching the jellyfish or the claws of the crabs.

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Three of our traps caught significantly more terrapins than the other seven.  These traps weren’t too near to each other, but they were all located at the edge of the main body of Queens Creek, as opposed to in the mouth of inlets into the marsh like the other traps were.  We had predicted that the latter traps would catch the terrapins venturing up to the marsh grass for food, but perhaps it’s easier to capture those that aren’t currently searching for something to eat.

Not everything went as planned this summer.  We lost two traps that were ripped off the wooden stakes holding them in place by strong tides during the full moon.  We almost lost two more, but we were able to see them sitting at the bottom of the creek and recover them.  A couple of times I incorrectly marked a terrapin, or one would fight its way out of my hands and over the edge of the canoe into the creek before I was done marking it.  And it took me a couple weeks to be able to confidently determine the sex of the terrapins.

But many things went well.  We caught more terrapins than we were expecting to, and the researchers sampling other sites also got a good amount of data.  I’ll have lots of data for the mathematical model and we’ll be able to get a fairly accurate estimate of the population size when we analyze the numbers in the fall.  Last but not least, I got some great field work experience that I really enjoyed.

I also made a lot of progress with the mathematical model I’ve been working on.  Since the last time I blogged about it, I’ve made a few changes, including adding a parameter for road mortality, r.  This represents the fraction of breeding females that are killed by cars as the come on land to nest.  The model now looks like this:

See last blog for explanation of other variables

See last blog for explanation of other variables

I’ve got my work cut out for me when it comes to research this coming year.  I’m really looking forward to finalizing the model and using it to predict the future of the local diamondback terrapin populations.   Hopefully we’ll be able to get a paper published soon, and I’m planning on using the data to complete an honors thesis this year.