It was a normal Friday on January 28th when I got to work. The phone
rang as soon as I hit the chair. My boss was on the other end saying "Get
your boots Kelly, someone has sighted a large sea turtle dead on the beach
in Esquimalt Lagoon." So we gathered a few helpers, loaded up the van
and made our way there. Our first hint of the turtle's location as we
started looking along the shore was the strong smell: I was glad we remembered
to bring a few large bags and some gloves.
We identified the specimen as a Green Sea Turtle (Chelonia mydas), the
largest of the hard-shelled sea turtles. The body was complete except
for one hind flipper and the head. Fortunately, the skull was found a
few feet away in the water. It had been picked clean, and the rest of
the body appeared to have been fed upon for a while as well. We never
found the hind flipper. The carapace measured 87 cm long and we guessed
the body weight to be around 45 kg. This was an average-sized specimen,
although Green Sea Turtles have been known to weigh up to 227 kg and get
as long as 1.2 m. When we finished measuring and photographing it, we
put the specimen into a bag for the trip back to the Museum, then placed
it in a freezer until we were ready to prepare the skeleton.
Green Sea Turtles have been known to eat a variety of marine debris including
plastic bags, plastic and styrofoam pieces, tar balls, balloons and plastic
pellets. We will examine the stomach contents to determine if that was
the cause of death in this case. If nothing conclusive is found in the
stomach, an autopsy is planned. This species is also vulnerable to a potentially
fatal development of fibropapillomas that appear as lobe-shaped tumors
around the appendages and neck. If any light is shed on the reason this
turtle came to an end, an update will be posted on the Museum's web site
at http://rbcm1.rbcm.gov.bc.ca.
The Green Sea Turtle belongs to the family Cheloniidae (see taxonomic
scheme below), along with most of the other marine turtles. The common
name refers to the colour of its fat. Green Sea Turtles and their eggs
have been important food items in many countries for hundreds of years,
and may still be -- regardless of the species classification as endangered
for the southeastern United States and threatened everywhere else. They
are found in the Atlantic, Indian and Pacific oceans, although there are
no permanent residents within B.C. waters. They normally breed and nest
in more tropical waters such as Mexico, the Galapagos Islands, Hawaii,
Costa Rica and Florida, USA. Some have been reported to migrate up to
1500 km to a nesting site.
The carapace, or shell, is smooth, dark green, has no keel and has a serrated
edge along the posterior margin. The carapace is made up of epidermal
plates. Each year a new and larger layer grows from underneath. The old
one remains above so that growth rings are apparent from the outside.
Aging turtles is possible by counting the rings, but after a while the
older rings wear away. A more reliable method of aging turtles is to section
the leg bones, which reveals the annual rings.
The males typically have a larger carapace, with the tail extending beyond
the carapace more noticeably. One claw is present on each front flipper
of the males. The adults are mainly herbivorous on Turtle Grass (Thalassia),
but may also feed on invertebrates such as jellyfish. Green Sea Turtles
spend most of their time in water, but have been seen basking in the sun
on rocks and beaches.
Turtles probably originated in the Triassic period some 200 million
years ago. Their ancestors were most likely some form of Cotylosaur in
the Carboniferous period 275 million years ago. Turtles seem to have retained
the more primitive anapsid skull (solid-roofed) with no holes on the sides.
This was characteristic of other reptiles during the Triassic. Today,
turtles are the only reptiles with this physical characteristic. Also
particular to turtles is the complete absence of teeth in herbivores and
in carnivores. Instead, the edges of the jaw have sharp ridges covered
with a tough horny beak. Turtles have good eyesight and they see in colour:
it is probably the main sense receptor.
The Royal BC Museum has one other specimen of Green Sea Turtle in its
collection. This first specimen was found beached near Ucluelet, B.C.
in December 1954.
Below is a taxonomic scheme to illustrate the placement of Green Sea
Turtles in our phylum.
| PHYLUM: |
CHORDATA (chordates) SUBPHYLUM: Tunicata
(sea squirts, doliolids, salps, appendicualians)
CEPHALOCHORDATA
SUBPHYLUM: Cephalochordata (lancelets)
SUBPHYLUM: Agnatha (vertebrates without jaws)
SUBPHYLUM: Gnathostomata (jawed vertebrates)
SUPERCLASS: Pisces (fish)
CLASS: Amphibia (amphibians)
CLASS: Reptilia (reptiles)
SUBCLASS: Testudinata (turtles)
Cheloniidae (hard-shelled marine turtles)
Chelonia mydas
Chelidae (freshwater turtles)
Carettochelydidae (freshwater turtle)
Dermochelyidae (leatherback turtles)
SUBCLASS: Lepidosauria (lizards and snakes)
SUBCLASS: Archosauria (crocodiles, alligators)
CLASS: Aves (birds)
CLASS: Mammalia (Mammals)
|
Additional reading on Green Sea Turtles:
http://www.bcc.orst.edu/~sappj/cmydas.html
http://www.seaworld.org/Sea_Turtle/seaturtle.html
http://www.vetmed.ufl.edu/sacs/wildlife/fibpap.html
http://www.turtles.org/toc.htm
http://www.ex.ac.uk/MEDASSET/ident.htm
http://www.turtles.org/library.htm
http://www.cccturtle.org/sat1.htm
