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Diamondback Terrapins of the New York City Area |
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The
familiar diamondback terrapin (Malaclemys terrapin)
lives year-round in the bays and estuaries of Gateway
National Recreation Area (see
this also). Summer visitors to Gateway often see nesting
terrapins, and this may the only reptile they ever see
in its natural habitat. The terrapin story is an interesting
one, in part because humans have had such dramatic impacts
on this harmless and appealing turtle.
Diamondback terrapins are the only turtles that live in
the ocean, except for the much larger sea turtles. Adult
female terrapins have shells 6-9 inches (15-23 cm) long,
while males reach only 4-5 ½ inches (10-14 cm)
long. |
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DISTRIBUTION
& HABITAT
Terrapin
populations occur along much of the East Coast and Gulf
Coast of the U.S. Although the length of this range
covers thousands of miles, terrapins only inhabit the
thin strip of estuaries and coastal marshes right along
the coast, so their actual range is quite small in area.
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| Terrapins
inhabit coastal marshes, tidal creeks, estuaries, bays
and coves. These waters are brackish; meaning
they are mixtures of fresh and salt water. Marshes containing
salt-marsh cordgrass (Spartina alteniflora) are
important feeding habitats for terrapins. Cordgrass marshes
can be seen in many places throughout Gateway NRA, at
the Jamaica
Bay Wildlife Refuge (JBWR) and the Sandy Hook Unit
in NJ. Cordgrass marshes look like flat islands of grass,
and are often covered by water during high tide. |
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NATURAL
HISTORY
Terrapins
primarily feed on invertebrates such as mollusks and
crustaceans. Where there are many terrapins, their active
foraging can have a significant impact on their prey,
and so terrapins may be an important component of coastal
food webs. However, it is probably impossible to truly
understand the natural ecological significance of terrapins
now, because their numbers have been so low for so long.
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Within
Gateway NRA, the only major terrapin nesting areas we
know of are in Jamaica Bay Wildlife Refuge and the Sandy
Hook Unit. The majority of the research on nesting terrapins
in our region has been conducted at JBWR, but these
results are probably typical of terrapins throughout
the region. Mating occurs in May and June, when aggregations
of more than 100 terrapins can sometimes be seen in
the offshore channels. In June and July, female terrapins
come on shore to nest, and this is when visitors have
most of their "close encounters" with terrapins.
They nest most commonly in dunes, grassland, shrubland,
beaches, and sand and gravel trails. Females lay 3 to
18 eggs per nest, but average about 11. Some females
can lay two nests per year. After nesting, females join
the males in the deeper bays and estuaries, where they
feed until hibernation.
Eggs
take 70 days or more to hatch, and some hatchlings emerge
in the late summer and early fall. The other hatchlings
overwinter in their nests, and emerge the following
spring. Like many turtles, terrapins grow slowly, taking
3-8 years to mature (males mature earlier than females).
No one knows how long they may live.
Survival
is tough for the diamondback terrapin at any stage in
life, but no age is as perilous as the incubation and
hatchling stages. Predators destroy many nests. Little
is known about behavior of terrapins that do manage
to hatch, but their survivorship is likely to be very
low. Hatchlings tend to avoid open water, and they prefer
burrowing under shoreline debris, mud and tidal wracks
of cordgrass. |
HISTORY
OF A MEAL
Terrapins
were once highly prized for their meat, and connoisseurs of
the nineteenth and early twentieth century considered them
a delicacy. Starting in the mid-1800s, terrapins were harvested
in huge numbers to make soup. This led to the loss of many
populations, especially those near large cities. The close
proximity to New York City, coupled with the fact that Long
Island terrapins were considered to be the best tasting on
the market, lead to severe declines in many local terrapin
populations. By the mid-1930s terrapins had become so rare
in the Long Island-New York City region that naturalists thought
the species was locally extinct.
Luckily
for terrapins, the onset of World War I and the Great Depression
resulted in a rapid end of the turtle soup industry. Since
that time, terrapin populations in many areas have slowly
and steadily recovered. This recovery is now threatened by
a number of new threats. |
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THREATS
TO TERRAPINS
Predation
– Predators such as raccoons and foxes often pose
a serious threat to turtle eggs, hatchlings, and occasionally
even adult turtles. While raccoons and foxes occur naturally
at Sandy Hook, neither originally occurred at JBWR.
Studies conducted at JBWR in the early 1980s suggested
that the great reproductive success of terrapins there
was due to the fact that there were no raccoons or foxes.
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| Nest
survivorship was an astonishingly high 93%! With
about 2,000 nests being laid each year, the Jamaica
Bay terrapin population became one of the largest
and most robust populations in New York State. However,
in the early 1990s, depredated terrapin nests were
seen in noticeable numbers at JBWR. Although nest
predation appeared to be minor until 1995, the situation
got worse. By 1998, over 1,300 depredated nests
were found at JBWR, and in 1999, more than 1,800
depredated nests were found. In the last few years
the survivorship of terrapin eggs has dropped to
less than 3%. While this is startling, this new
rate is actually quite similar to rates seen at
terrapin populations elsewhere in their range. |
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The
cause of this change? A dramatic increase in the raccoon population.
Little is known about how raccoons colonized JBWR or how many
live there now. Park officials attribute the increase in raccoons
to humans, because people sometimes release "nuisance"
urban raccoons into parks. Not only is this illegal, but it
obviously harms native species. The availability of garbage
has probably also played a role in raccoon population increases.
The impact
of other predator species is not as well studied as that of
raccoons. Foxes occur in the Sandy Hook Unit. Laughing gulls
and crows may also eat terrapin nests in Gateway. In addition
to these nest predators, "root predation" has been
observed at JBWR. This occurs when the roots of beach plants
actually invade a nest, penetrate eggs, and absorb their nutrients.
Development
– A number of other human actions harm adult terrapins,
as well as eggs. One important threat to terrapin survival
is development of their habitats. Dredging, filling, and marshland
alterations reduce the aquatic habitat critical to terrapin
survival. In our area, lawns and bulkheads now replace many
of the areas that were once terrapin nesting beaches.
Collection
– Although terrapins will never be harvested like they
were during the heyday of the soup industry, harvesting and
collection continues today. It is illegal to harvest or remove
terrapins from GNRA without a permit. Many terrapins unintentionally
drown as bycatch in crab pots. Fitting crab traps with Bycatch
Reduction Apparatus (BRAs), as is occurring in New Jersey,
can reduce incidental" bycatch.
Other
Threats Posed by Humans – Especially around
urban regions, tide-borne debris may harm nesting terrapins
and hatchlings. Automobiles also injure and kill terrapins.
Hundreds of terrapins are killed on Long Island and New Jersey
roads each year. Marine vehicles such as boats, wave-runners
and jet-skis may also kill terrapins in our local waters.
Release of Captive Terrapins – While releasing
turtles from pet stores and food markets might seem like a
humane action, it is illegal and may be dangerous to local
populations. Released turtles may introduce new diseases into
native populations, with potentially disastrous results. |
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SOLUTIONS
The
future of diamondback terrapins at Gateway is uncertain.
The Sandy Hook population appears to be large and stable.
At Jamaica Bay Wildlife Refuge, raccoons are a new and
serious problem, and that terrapin population appears
to be vulnerable.
Visitors
are strongly discouraged from doing anything that might
disturb terrapins because human disturbance can prevent
females from nesting. While it is temping to approach
a terrapin, remember, these wild animals are afraid
of humans. The best way to view terrapins is with binoculars,
at a minimum of 150 feet. That way, you are less likely
to scare a terrapin and more likely to witness nesting
take place. If you encounter a terrapin up close, try
to walk past it as quietly and quickly as possible.
Be sure to let park staff and a researcher (see below)
know where and when you see turtles, so they can add
your observations to the ongoing research.
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At
JBWR, the Park Service has taken measures to reduce human/terrapin
encounters by closing the sand trail (known as the "Terrapin
Trail") during the critical nesting season. Unfortunately,
some visitors ignore this closure. Trespassing onto the
trail during this time is not allowed. Please respect
this rule.
In addition to walking with caution, care should also
be taken while driving the roads in and around Gateway.
Drive slowly and carefully to avoid hitting terrapins
crossing roads, especially in June and July.
Visitors should also be aware that collection of terrapins
anywhere in Gateway is harmful to the overall population,
and is also ILLEGAL. |
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| RESEARCH
In
an effort to learn more about diamondback terrapins,
the Park Service at Gateway NRA and researchers from
the Department of Biology, Hofstra University, continue
to study terrapins throughout the Park. Research efforts
are focused on studying the raccoon population, collecting
more information on the nesting biology of terrapins,
learning more about remote nesting sites, studying the
daily and seasonal movements of terrapins, and making
better population estimates. As researchers learn more
about Gateway terrapins, more can be done to help preserve
this population. Each year a large volunteer effort
makes this possible, and your help would be greatly
appreciated.
If you would like to learn more about terrapins or about
opportunities to participate in the on-going research
in this area, please contact:
Dr. Russell Burke
Department of Biology, Hofstra University
Hempstead, NY, 11549
(516) 463-5521
Click here to find out
more. |
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