Photo-Diary of a Terrapin Researcher Don Lewis, Massachusetts Audubon Society, Fox Island Wildlife Management Area

The Whole Shebang: The Story of Terrapin 1233
— 11 October 2002

The 2002 diamondback terrapin season has drawn to a quiet close as fall deepens its grip on the Land of Ooze.  Nighttime temperatures dipping into the 40s triggered brumation instincts, and turtles paddled back to their protected creeks to cozy into soft muddy hibernacula.  Nests have largely hatched; only an isolated few remain.  And on Thursday a dead Kemp’s ridley, the rarest sea turtle in the world, was recovered by a ranger on Sandy Neck in Barnstable.  While a bit too early to register as an official cold-stunned sea turtle, it hints that the stranding season is only a couple of weeks away.  Heeding these autumnal clues, Bob Prescott — director of Mass Audubon’s Wellfleet Bay Wildlife Sanctuary — and I swept the low-tide drained channels off Blackfish Creek to clear potentially lethal debris this last week.  After three years of aggressive clean-up, the amount of dangerous material and ghost equipment has dropped significantly.

One of the last 2002 nests to hatch offers a review of the terrapin season in microcosm.  It’s fairly rare to see any turtle more than once or twice a year.  In the case of Terrapin 1233, though, luck intervened and gave us a rather complete record of her entire year, in the process teaching us a lot about the lifecycle of diamondbacks in their northernmost clime.

Chipman’s Cove lies in the northeast corner of Wellfleet harbor.  The cove is a shallow protected embayment with a dark, rich bottom.  As such it heats up very early in the year and presents a prefect habitat for foraging females and has consequently become the veritable singles bar for the whole estuary system.  We’ve even dubbed it “the gene pool” because turtles from throughout Wellfleet Bay paddle to the cove immediately after emerging from brumation to mix, mingle, and fatten up for the heavy burden of two annual clutches, each one about 10 percent of their body mass.  For a brief period each late May and early June, it seems like every turtle within a five-mile radius has traveled to Chipman’s Cove to find Mr. or Ms. Right.  Then they scatter again to nesting sites everywhere around the bay except for Chipman’s Cove itself.

On May 19th, I launched my kayak into the cove in search for terrapins (see Melting Pot).  Despite blustery northwest winds, I managed to net six mature female turtles, one of whom was Terrapin 1233.  An 11-year-old lady seen for the first time this day, she measured 17.85 centimeters straight-line carapace length and 15.8 centimeters plastron; she weighed 978 grams coming directly out of brumation and sported a few scute anomalies.  Her 5th vertebral was split into two sections, and she had an extra marginal scute on each side — something we call “split 9/90 marginals.”  (See Terrapin Identification: Marginal Notching System.)

A couple of days later a recaptured 1233 among nine other females and two males, all in Chipman’s Cove.  Her weight had dropped to 949 grams.

The next time we saw her was on the morning of 21 June when Chris Burns (see A Nesting Homerun) spotted her on Lieutenant Island’s 5th Avenue, just as she had finished laying her first nest of the year.  After this initial clutch, her body weight had dropped to 830 grams, less than 85 percent of her brumation weight.

Nineteen days later, to the very hour, I saw Terrapin 1233 digging her second clutch in a driveway off 5th Avenue at 10 a.m. on 10 July.  Because this nest was dug in such a heavily used parking pad, I decided to harvest the eggs and relocate them to a safer spot. I probed the rough area behind her and discovered the egg chamber.  There were 13 eggs which weighed a total of 95 grams.  Terrapin 1233 weighed only 767 grams after laying this nest (#214), under 80 percent of her springtime weight!  The eggs were placed under a predator excluder on a sandy bank off the Lowland Road where they remained until 23 September.  Following a series of early fall storms, the slope began to erode, prompting me to harvest these nearly mature eggs and finish their incubation inside my garage lab.

Egg # L W Wt 093 3.04 2.07 7.6 103 3.09 2.16 7.9 102 3.14 2.02 7.6 097 3.14 2.08 7.6 104 3.15 2.00 7.4 100 3.15 2.05 7.5 098 3.18 2.07 7.9 094 3.19 2.04 7.6 096 3.22 2.21 8.9 095 3.25 2.02 7.6 099 3.25 2.21 9.0 101 3.28 1.97 7.4 105 3.28 2.05 7.8

I was a bit surprised to learn that the eggs had increased their combined mass by more than 7 percent to 101.8 grams since they were deposited on 10 July — presumably absorbing moisture through the egg shell.  Another nest (#146) harvested on 29 September showed a weight gain for 16 eggs from 131 grams to 151.7 grams, over 15 percent increase in mass.

For the record, the table at the right shows the measurements of Nest 214 in ascending size order, based on maximum length.  (L=length. W=width Wt=weight, in centimeters and grams.)

Hatchlings from Nest 214 began to emerged on 9 October.  After two popped from the moist, sandy bucket, I exposed the chamber to find all but one turtle ready to emerge.  The last one was left in the incubation container until it, too, emerged on 11 October.

Of the 13 babies, three showed anomalies.  Hatchlings 609 and 610 had a split rear marginal on the right side.  Hatchling 617 sported split rear marginals on both sides as well as a 5th vertebral split into three scutes.

Hatchling      CL      CW       PL      Wt
    618         2.57     2.28     2.24     5.2*  
    606         2.61     2.31     2.32     5.5 
    611         2.62     2.26     2.29     5.6 
    608         2.63     2.29     2.30     5.6 
    613         2.63     2.37     2.35     5.6 
    607         2.65     2.24     2.37     5.4 
    609         2.67     2.30     2.39     5.4 
    610         2.68     2.37     2.31     5.9 
    616         2.69     2.34     2.35     5.7 
    614         2.70     2.28     2.39     5.6 
    612         2.71     2.34     2.36     5.9 
    617         2.72     2.28     2.39     5.9 
    615         2.74     2.25     2.35     5.6

    * = runt and last to emerge.

For the record and for comparison, the table at the right shows their measurements and weights, also in asscending size order.  (CL=carapace length, CW=carapace width, PL=plastron length, Wt=weight, in centimeters and grams.)

Total hatchling mass amounted to 72.9 grams or nearly 77 percent of the clutch weight when laid and almost 72 percent of the weight on 23 September.

Finally, a family portrait below of 1233 and most of her second-clutch hatchlings offers enticing hints about similarity and diversity of carapace designs.

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