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Don Lewis, Massachusetts Audubon Society,
Fox Island Wildlife Management Area

Sex and the Single Turtle — 10 May 2001

Last night, spring threw us one final curve with temperatures probing the upper 30s.  As I left for the creek this morning, the thermometer read 41 degrees.  Luckily the wind had dropped to a mere 5 knots out of the north.  In other words, it was a delightful day for wading in the rip even though the number of terrapins alert and moving with the tide is still fairly limited.  And none were snorkeling for air as they swept through the rapids.  Instead, they hunkered along the bottom where water temperatures were more terrapin friendly.

Turtle 1006 paddled through about 90 minutes before ebb tide.  She’s a mature female whom we last saw just five days ago as she ran the murky rapids on Cinquo de Mayo.  Since then she’s dropped 18 grams in weight.

The next two captures, #1061 and #1063, proved extremely interesting and instructive.  Terrapin 1061 is a sexually mature 7-year-old male; Terrapin 1063 is a pre-pubescent 5-year-old female.  They were both the identical length, 11.2 centimeters, and nearly the same weight, 250 grams.  And they pose one of the more difficult challenges for the amateur field researcher: distinguishing gender differences between a mature male and a young female before puberty, that is, before obvious size dimorphism kicks in.

From the topside, you can detect the rounder, plumper form of the juvenile female (#1063 on the right) than the shallower-shelled male (#1061 on the left).

Looking at the bottom, the thicker male tail of #1061 on the right can be compared with the thinner female tail of #1063 on the left.  Note also the relatively longer plastron length of the female on the left (87.5% of carapace length) to the male plastron on the right (less than 82% of carapace length).

Captured together, they provide a great visual lesson for terrapin field researchers.

Finally, in response to several reader concerns, we have installed an OSHA-certified ballet bar in the dinghy, so that terrapins in the processing queue can keep in top form while waiting for release.

And you’ll be pleased to note that this stretching exercise seemed to have had immediate positive results.  Kick, stroke, kick, stroke.