Environmental Engineering Reference
In-Depth Information
information were still able to maintain a direction of orientation, but when both cues
were removed the turtles were disoriented (Avens and Lohmann, 2003). The mag-
netic map sense exhibited by hatchlings is also thought to allow female sea turtles to
imprint upon the location of their natal beaches so that later in life they can return
there to nest. This phenomenon is termed
natal homing
(Lohmann et al., 2008b), and
it serves to drive genetic division among subpopulations of the same species. As a
result, altering magnetic fields near nesting beaches could potentially result in altered
nesting patterns. Given the important role of magnetic information in the movements
of sea turtles, impacts of magnetic field disruption could range from minimal (i.e.,
temporary disorientation near a cable or structure) to significant (i.e., altered nesting
patterns and corresponding demographic shifts resulting from large-scale magnetic
field changes) and should be carefully considered when siting projects.
SIDEBAR 7.1. With Regard to Turtles
Marine turtles have outlived almost all of the prehistoric animals with which they once
shared the planet. Five species of marine turtles frequent the beaches and offshore waters of
the southeastern United States:
•
Loggerhead turtles
are the most common turtles to nest in Florida. Over 50,000
loggerhead nests are recorded annually in Florida. This turtle is named for its
disproportionately large head, and it feeds on crabs, mollusks, and jellyfish.
•
Green sea turtles
are the second most common turtles in Florida waters. Green
sea turtles are the only herbivorous sea turtles. They feed on seagrasses in shallow
areas through the Gulf. The lower jaw is serrated to help cut the seagrasses it eats.
•
Kemp's ridley sea turtles
are the rarest sea turtles in the world. They primarily
nest on one beach on the Gulf Coast of Mexico and are the smallest species of
sea turtle. Scientists have been trying to transplant Kemp's ridley eggs to Texas to
establish a new nesting colony. They are the only species of sea turtle known to
lay their eggs during the day.
•
Leatherback sea turtles
are the largest sea turtles in the world; they can be over
6 feet long and weigh 1400 pounds. The leatherback does not have a hard shell,
but rather a leather-like carapace with bony ridges underneath the skin. The leath-
erback makes long migrations to and from its nesting beaches in the tropics as far
north as Canada. Jellyfish are the favored prey for these turtles.
•
Hawksbill sea turtles
are usually found feeding primarily on sponges in the south-
ern Gulf of Mexico and Caribbean. The hawksbill sea turtle was hunted to near
extinction for its beautiful shell which features overlapping scales.
All five are reported to nest, but only the loggerhead and green turtle do so in substantial
numbers. Most nesting occurs from southern North Carolina to the middle west coast of
Florida, but scattered nesting occurs from Virginia through southern Texas. The beaches
of Florida, particularly in Brevard and Indian River counties, host what may be the world's
largest population of loggerheads (Dodd, 1995).
Marine turtles, especially juveniles and subadults, use lagoons, estuaries, and bays as
feeding grounds. Areas of particular importance include Chesapeake Bay, Virginia (for
loggerheads and Kemp's ridleys); Pamlico Sound, North Carolina (for loggerheads); and
Mosquito Lagoon, Florida, and Laguna Madre, Texas (for greens). Offshore waters also
support important feeding grounds such as Florida Bay and the Cedar Keys, Florida (for
green turtles), and the mouth of the Mississippi River and the northeast Gulf of Mexico (for
Ke m p's r id leys).
