Vol9

What We’ve Been Doing

Some of our most important ongoing projects:

  • Nests, hatchlings, and adult survivorship: These have been our main, consistent goals from the beginning of the project, starting with Jeremy Feinberg’s work in 1998. Each year we monitor nests that are laid. Most years we measure nest and hatchling success, and the long-term mark-recapture of adult females allows us to measure adult survivorship. One of our major findings is the large amount of variability we observe between years in each of these factors.
  • Reproductive variables: In most years we have excavated at least some nests, and thus we have long term data on clutch size, egg size, and clutch frequency. Again, we have detected long-term changes in each of these variables, which have resulted in a major decrease in the number of eggs laid.
  • Egg viability: One of our initial concerns was that egg viability would be low, because of all the pollutants in Jamaica Bay. Because terrapins are so long-lived, we suspected they might be carrying large and potentially dangerous pollutant loads that could harm egg viability. But HU graduate student Maria Giambanco’s work in 2001 & 2001 showed that egg viability is generally high.
  • Temperature sex determination (TSD): One fascinating characteristic of turtles is the large number of species with temperature sex determination, something that seems weird to us mammals. It has been known since 1991 that terrapins have TSD, but we were the first to work out the details (which temperatures produce which sex), and at what point during incubation temperature influences sex. With these data we are now back-calculating hatchling sex ratios in past years.
  • Hatchling and adult movements: Starting with HU graduate student Kerry Muldoon’s work (2006-2008), we have completed the major work so far on hatchling movements after terrapins leave the nest. Muldoon and student Neil Duncan have found that hatchlings often move upland to overwinter on land. This behavior is unlike that of any other aquatic turtle, and is truly puzzling. Tracking adults has been far more difficult and our data on this are  really sparse.
  • Adult diet: Kayleigh Erazmus’s work 2008-2010 on JB terrapin diets showed that they change dramatically year-to-year and that they include a high percentage of plant material, mostly algae. We continued her work and now have five years’ worth of diet data. JB terrapins eat differently, and probably worse, than terrapins elsewhere.
  • Spatial distribution of nests: Graduate student Sylwia Ner mapped out terrapin nests all over Jamaica Bay and Sandy Hook NJ in 2000-2002. She showed that nearly all nesting occurs on the island of Rulers bar, which was the final word until 2009 when the JFK population exploded.
  • Raccoon population size and diets: Kat Broadwater (Atkinson) started our raccoon work in 2001 & 2002, Eric Rulison worked on it most recently, in 2006-7. There are 50-100 raccoons on Rulers Bar; some live 6 years or more. They eat a lot of crustaceans, and terrapin eggs are a small part of their diets.
  • Nest site choice: Amanda Widrig (Scholz) holds the record for the most intact JB terrapin nests found in one year (144 in 2004). She found that nest depth, precipitation, and grass cover all influence nest site choice, root predation, and hatching success. In hot dry years, it is better to be in a deep nest, and in cold wet years it is better to be in a shallow nest.
  • Age determination: Traditionally, many turtle researchers have assumed they could accurately estimate a turtle’s age by counting the rings on its scutes (while acknowledging that old turtles lose rings, and that all rings eventually become smooth). But a number of studies have shown that rings are not necessarily annual. This matters to us because we’d like to make robust estimates of age. So we have been making plaster casts of scutes to see if JB terrapins lay down a new ring each year.
  • Nocturnal nesting: We conduct almost all our nesting surveys in the daytime because that’s so much easier and it seems that’s when most of our girls nest. But we also know we miss many nesters—are those nocturnal? We’ve spent a couple of years looking at this (mostly by then high school student Yi-Hsin Chen raking beaches and looking at tracks) and found that there is little nocturnal nesting at JB, which is surprising because nocturnal nesting  happens a lot north and south of us.
  • Hatching synchrony: In most turtle species, when it’s time to emerge, everyone comes out at once. At JB, we have every possible combination—sometimes they all emerge together in the fall, sometimes they trickle out one or two at a time over weeks, sometimes some of the hatchlings emerge in the fall and the rest in the spring.
  • Sex identification: We know terrapins have temperature sex determination; what does this mean in the lab?Amanda Widrig (Scholz) (2004-5) recorded nest temperatures in  many nests, and using those records and the work done by Artie Calichio (2009-10) we can predict with some confidence that most hatchlings are female. But to confirm this we’d like a technique to reliably sex hatchling terrapins, and we’ve been working on this.
  • Parasite ecology: When they left their freshwater relatives and switched to salt water, it seems terrapins left many types of parasites behind. But they picked up some new ones, including barnacles and the nematode Pleurogonius malaclemys. Mud snails are the intermediate host and terrapins are the obligate final host for P. malaclemys; terrapins get infected by eating infected mud snails. I care about this because it is easy to count the parasites on mud snails, and the number of parasites on mud snails is an indicator of the number of terrapins in the local area.

 

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