Environmental Engineering Reference
In-Depth Information
Offshore reefs provide feeding and resting habitat (for loggerheads, greens, and hawks-
bills), and offshore currents, especially the Gulf Stream, are important migratory corridors
(for all species, but especially leatherbacks).
Note:
Raccoons destroy thousands of sea turtle eggs each year and are the single
greatest cause of sea turtle mortality in Florida.
Most marine turtles spend only part of their lives in U.S. waters. For example, hatch-
ling loggerheads ride oceanic currents and gyres (giant circular oceanic surface currents)
for many years before returning to feed as subadults in southeastern lagoons. They travel
as far as Europe and the Azores, and even enter the Mediterranean Sea, where they are
susceptible to longline fishing mortality. Adult loggerheads may leave U.S. waters after
nesting and spend years in feeding grounds in the Bahamas and Cuba before returning.
Nearly the entire world population of Kemp's ridleys uses a single Mexican beach for
nesting, although juveniles and subadults, in particular, spend much time in U.S. offshore
waters (Dodd, 1995).
The biological characteristics that make sea turtles difficult to conserve and manage
include a long life span, delayed sexual maturity, differential use of habitats among species
and over the turtles' life stages, adult migratory travel, high egg and juvenile mortality,
concentrated nesting, and vast areal dispersal of young and subadults. Genetic analyses
have confirmed that females of most species return to their natal beaches to nest (Bowen et
al., 1992, 1993). Nesting assemblages contain unique genetic markers showing a tendency
toward isolation from other assemblages (Bowen et al., 1993); thus, Florida green turtles
are genetically different from green turtles nesting in Costa Rica and Brazil (Bowen et al.,
1992). Nesting on warm sandy beaches puts the turtles in direct conflict with human beach
use, and their use of rich offshore waters subjects them to mortality from commercial fisher-
ies (National Research Council, 1990).
Marine turtles have suffered catastrophic declines since the European discovery of the
New World (National Research Council, 1990). In a relatively short time, the huge nesting
assemblages in the Cayman Islands, Jamaica, and Bermuda were decimated. In the United
States, commercial turtle fisheries once operated in south Texas (Doughty, 1984) and in
Cedar Keys, the Florida Keys, and Mosquito Lagoon in Florida; these fisheries collapsed
from overexploitation of the mostly juvenile green turtle populations. Today, marine turtle
populations are threatened worldwide and are under intense pressure in the Caribbean basin
and Gulf of Mexico, including Cuba, Mexico, Hispaniola, Bahamas, and Nicaragua. Marine
turtles can be conserved only through international efforts and cooperation (Dodd, 1995).
A number of interesting questions related to turtle migration remain unanswered. For
example, how do turtles find their way precisely back to their natal beach over their vast
travel distance? Do turtles imprint, as salmon do, on olfactory features in the water or is the
location pinpointed using geomagnetic information?
Sea turtles have migration patterns somewhat similar to that of salmon. After hatching
and entering the sea and facing and surviving the tribulations presented by the elements and
predators, and after spending time in their sea feeding grounds, the females return to their
natal grounds. Adult females lay eggs in the sand. Turtles may use the geomagnetic field to
tell them their location and to lead them to their natal grounds (Goff et al., 1998).
The emphasis of most of these studies is on the value of magnetoreception for
navigation; marine and hydrokinetic energy technologies are unlikely to create
magnetic fields strong enough to cause physical damage. For example, Bochert and
Zettler (2006) summarized several studies on the potential injurious effects of mag-
netic fields on marine organisms. They subjected several marine benthic species (i.e.,
