Plymouth Red-bellied Turtle

The Plymouth Red-bellied Turtle (Pseudemys rubriventris)
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Pseudemys rubriventris bangsi, also known as the Plymouth Red-bellied Turtle, or the Northern Red-bellied Cooter, has been listed as endangered and protected under the Endangered Species Act of 1973 since April 2, 1980 (3).  Until recently, the turtle was classified taxonomically as a subspecies due to differences in shell morphology (4).  When it was later found that this species showed no difference in morphology or genetics from the mid-Atlantic Red-bellied Turtles Pseudemys rubriventris (4), the National Wilderness Institute filed a petition in 1997 asking that Pseudemys rubriventris bangsi be removed from the endangered species list due to taxonomical error at the time of listing (2).

The loss of federal protections and the associated recovery plan could have resulted in drastic population declines.  In 1996, there was new criteria for which a species could be considered endangered; this was beneficial to protecting the Plymouth Red-bellied Turtle (3).   The 1996 Disjunct/Discrete Population Segment Policy allows populations to be considered on their own for extinction risks if there is significant reproductive isolation (3).  This lack of interbreeding with the rest of the species could be due to physiological, behavioral, ecological and/or physical factors (3).  In the case of Pseudemys rubriventris bangsi, the nearest population is approximately 250 miles south; this significant isolation distance may have existed for hundreds of years (3).  Isolation and the lack of any migratory evidence have led to the Plymouth Red-bellied Turtle being granted the status of a discrete population segment, under which it maintains its endangered designation under the Endangered Species Act (3).  Many recommend that the name bangsi be retained, even though it is no longer an official subspecies.  Some experts claim that the extinction of the Plymouth population would result in a 40 % reduction in the range of the species (3).

The carapace of the red-bellied turtle can measure from 10 – 16 in and is dark brown or black in color (1,3).  The scutes (modified scales) on the carapace are flat and nearly concave (1).  There is also a red bar on the marginal scutes.  The name red-bellied comes from the reddish color of the plastron, which is also accompanied by dark markings (1).  Sexual dimorphism is evident at 5 to 7 years (3) with males having long, straight claws on front limbs (1).

Pseudemys rubriventris bangsi must cope with harsh winters that are not experienced by mid-Atlantic populations of Pseudemys rubriventris (3). Winter research utilizing SCUBA has observed Plymouth Red-bellied turtles sleeping exposed on the bottom of ponds as opposed to being burrowed in the mud.  This occurs despite ponds being completely frozen (5).  Pseudemys rubriventris bangsi has also been observed making small jaw movements to draw in water for buccopharyngeal gas exchange (3,5).   Other observations included more movement under ice cover than previously thought.  Radio-telemetry showed movements of 7.6 m per week, although during some weeks they remained motionless (5).    These underwater movements increased to 36 m per week after ice melt (5).

Pseudemys rubriventris bangsi has a life expectancy of 40 to 45 years and does not reach sexual maturity until 15 to 20 years in age (3).  Females dig terrestrial nests near ponds and lay one to two clutches per year, although one is more typical (3).  The incubation period is 73 to 80 days and the temperature required is 25ºC (3).   Sex determination of the offspring is dependent on temperature, with cooler temperatures producing more males (3).  Due to closed forest canopies at nesting areas, an increasing percentage of nests are lacking the required sunlight needed to produce females.  In Boot Pond, this has resulted in a reported ratio of 21 males to every eight females.  This unequal sex ratio is limiting to the effective size of the population (3).

There are currently 20 ponds in Plymouth County Massachusetts, a region in Southeastern Massachusetts experiencing increasing land development, that are inhabited by Pseudemys rubriventris bangsi (3).  The ponds are land-locked coastal plain ponds fed by groundwater, springs and connected by an underground aquifer (3).  As much as 50 % of the population inhabits Federal Pond, which is owned and utilized by Federal Furnace Cranberry Company (3).  Plymouth County is being developed quickly and the Cranberry Company has been reviewing development opportunities which could endanger the turtle even more (3). Although Southeastern Massachusetts cranberry agriculture draws nearly 3.5 billion gallons of water per year from local surface waters, Red-bellied turtles have a better chance of continuing their existence by depending on the same water as cranberry growers than sharing their ponds with residential development.

The mid-Atlantic populations of Pseudemys rubriventris live in different habitats compared to their Northern disjuncts.   They inhabit rivers, creeks, interconnected pond habitats, and/or brackish water (3).  While Pseudemys rubriventris bangsi have to travel in upland areas to migrate to another pond, the mid-Atlantic population of Pseudemys rubriventris can travel huge distances by water (3,4).  Not only do they have different pressures in the winter, they also have different dispersal strategies and associated food webs (3).

The main threats to the Plymouth population are habitat loss, altered habitat, and high predation (3).  Ponds that previously had sunny shores ideal for egg incubation now are surrounded by a closed canopy due to intentional suppression of forest fires that use to occur naturally due to Native American fires and lightning (3).   Cooler temperatures in the shade have resulted in loss of nesting habitat and an unequal sex ratio as described above (3).

There is very little habitat protected for these turtles.  Crooked Pond is protected in the Massasoit National Wildlife Refuge, and East Head Pond is in the Myles Standish State Forest, but a neighboring cranberry grower holds the water rights (3).  There is a nesting beach protected on Island Pond and Gunner’s Pond, but the entire pond is not protected (3).

During the incubation period, and in the first few years of life, Pseudemys rubriventris bangsi experiences very high predation.  Nest predation, which can be as high as 100% for nests that are not protected at Federal pond, is carried out by crows, red fox, skunks, raccoons and coyotes, while hatchlings are preyed on by largemouth bass (Micropterus salmoides), chain pickerel (Esox niger), snapping turtles, great blue heron and bull frogs (Rana catesbeiana) (3, 6).   Analysis of the stomach contents of bull frogs provides evidence that they are one of the main predators of hatchlings (6).   The survival rate of hatchlings is thought to be very low.  Similar freshwater turtles, such as Blanding’s turtle, may have a hatchling survival rate of only 1% (3).  It is difficult to study the survival rate using the current shell notch identifying technique, because the notches are no longer discernable when the turtles are recaptured as adults (3).

The Headstart program is at the core of the recovery plan for the Plymouth Red-bellied Turtle.  Due to high predation, one of the main strategies in the recovery plan is to protect nests and take hatchlings from the wild.  The hatchlings are raised in captivity in 84ºF water and fed a head of romaine lettuce per day until they grow to be much larger than their non-headstarted counterparts.  This strategy allows turtles to reach a size large enough to avoid much of the predation that threatens them in the wild.  Studies have shown that carapace lengths of 66-95 mm and 296 mm increase survival rates to high levels (6).  Sometimes the headstarted turtles are six times larger than they would be if they had been left in the wild as a hatchling (6).  The first headstarted turtles were taken in 1984 and released in 1985.  Since then, 2725 turtles have been headstarted through this recovery effort (3).   Headstarted turtles, along with having a higher survival rate, also reach sexual maturity sooner (3).

Table 1: Number and locations of HS hatchlings in Plymouth County, MA from 1984-2006 (3).

plymouthredbellytable
(Click on Image to see data)

The recovery plan lists the criteria necessary for changing the ESA status from endangered to threatened as having 600 breeding adults in 15 or more self-sustaining populations of 50 or more turtles.  Delisting the turtles would require 1000 breeders in 20 self-sustaining populations.  The current population estimates suggest that there may be between 400 and 600 breeders in the current population in 20 ponds, but only 10 of these ponds contain more than 20 breeders, and very few are protected ponds.  These populations, as you can see from table 1, have received many turtles through the headstart program.  It is not known how the population would respond if the headstart program was stopped.  Even if the population goals are met in the near future, the sustainability goal of the populations may not be met for some time.   In order for the populations to be self-sustainable, a solution to the low survival of hatchlings in the wild is needed.

References:

1. US FWS Species Profile: Plymouth Red-Bellied Turtle (Pseudemys rubriventris bangsi) http://ecos.fws.gov/speciesProfile/SpeciesReport.do?spcode=C021

2. Michael J. Amaral, New England Field Office,  Endangered and Threatened Wildlife and Plants; 90-Day Finding on a Petition to Delist the Plymouth Redbelly Turtle (Pseudemys rubriventris bangsi) 71 FR 58363 58364,  10/03/2006  http://frwebgate.access.gpo.gov/cgi-bin/getdoc.cgi?dbname=2006_register&docid=fr03oc06-35 Accessed: Feb 20, 2008

3. Michael J. Amaral.  Northern Red-bellied Cooter (Pseudemys rubriventris)  5-Year Review: Summary and Evaluation May 3, 2007  U.S. Fish and Wildlife Service New England Field Office Concord, New Hampshire http://ecos.fws.gov/docs/five_year_review/doc1109.pdf

4. Robert A. Browne; N. Alison Haskell; Curtice R. Griffin; Jeffrey W. Ridgeway Genetic Variation among Populations of the Redbelly Turtle (Pseudemys rubriventris)
Copeia, Vol. 1996, No. 1. (Feb. 2, 1996), pp. 192-195.

5. Aquatic Oxygen Consumption by Wintering Red-Bellied Turtles  Terry E. Graham; Robert W. Guimond Journal of Herpetology, Vol. 29, No. 3. (Sep., 1995), pp. 471-474.

6. Size Related Survival of Headstarted Redbelly Turtles (Pseudemys rubriventris) in Massachusetts Alison Haskell; Terry E. Graham; Curtice R. Griffin; Jay B. Hestbeck Journal of Herpetology, Vol. 30, No. 4. (Dec., 1996), pp. 524-527.

 

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