Social and Economic Aspects of Sea Turtle Conservation
375
They apparently breed with females that pass by during their migrations to their
nesting beaches, or on feeding grounds where turtles congregate from several
different rookeries. This male-mediated gene flow will exacerbate the difficulty in
determining effective population sizes with any accuracy, because we will have
to quantify the effect and delineate the mating systems. In any case, it is likely
that the maintenance of genetic variability in wild sea turtle populations will
require effective population sizes of many thousands of adults and total population
sizes of perhaps hundreds of thousands, if not millions, when we include young
juveniles and neonates in our calculations.
14.9.2 P ROVIDING E COLOGICAL AND E COSYSTEM F UNCTIONALITY
We have known for some time that sea turtles may play important roles in maintaining the structure of coral reefs and seagrass beds (see Chapter 10, this volume).
Bouchard and Bjorndal (2000) demonstrated that nesting loggerheads are an
important link in moving nutrients and energy between marine and terrestrial
ecosystems. Using their figures for loggerhead nests, Frazer (2001) speculated on
the magnitude of materials moved onto Caribbean beaches prior to the reduction
of green turtle populations by European colonization of the New World. Using an
estimate of 34,000,000 adult green turtles in the pre-Columbian Caribbean (see
Jackson, 1997; Bjorndal et al., 2000) and assuming that half of them were females,
Frazer (2001) estimated that they would make 23,800,000 nests per year (4.2 nests
per female with a 3-year average remigration interval). That would have resulted
in a contribution of some 1,600,000 kg of organic matter, 365,000 kg of lipids,
170,000 kg of nitrogen, 15,500 kg of phosphorus, and 44,500,000,000 kJ of energy
to Caribbean beaches each year. Actual figures may have been higher, because
green turtles tend to lay their eggs higher up on the beach than do loggerheads
(Bouchard and Bjorndal, 2000). One can only wonder at the likely results and
impact of greatly curtailing these previous levels of annual inputs into terrestrial
systems.
Such speculation is an interesting pastime but does not really provide useful
information in determining how many turtles we need. How many nesting turtles
does it take to maintain a healthy level of nutrients on a beach? How many hawksbills
are necessary for the proper maintenance of a productive coral reef (Meylan, 1988;
see also Chapter 10, this volume)? How many green turtles are needed per hectare
of seagrass bed to sustain optimal productivity of such systems? Although we
admittedly do not know with any accuracy how many sea turtles of each species are
necessary to restore or sustain their prehistorical ecological and ecosystem function,
it is likely that it will require populations or meta-populations on the order of 10 4 –10 7 .
However, if we desire these population levels, it may also be necessary to restore
seagrass beds and coral reefs to their former levels of extent prior to human influences
in order to support prehistorical numbers of turtles (Jackson 1997; Bjorndal et al.,
2000). Such an undertaking is practically impossible; it would require the re-development or restoration of coastal habitats throughout the planet and displace millions
of humans from their homes and livelihoods.
1123 book.book Page 375 Monday, November 11, 2002 11:11 AM
375
They apparently breed with females that pass by during their migrations to their
nesting beaches, or on feeding grounds where turtles congregate from several
different rookeries. This male-mediated gene flow will exacerbate the difficulty in
determining effective population sizes with any accuracy, because we will have
to quantify the effect and delineate the mating systems. In any case, it is likely
that the maintenance of genetic variability in wild sea turtle populations will
require effective population sizes of many thousands of adults and total population
sizes of perhaps hundreds of thousands, if not millions, when we include young
juveniles and neonates in our calculations.
14.9.2 P ROVIDING E COLOGICAL AND E COSYSTEM F UNCTIONALITY
We have known for some time that sea turtles may play important roles in maintaining the structure of coral reefs and seagrass beds (see Chapter 10, this volume).
Bouchard and Bjorndal (2000) demonstrated that nesting loggerheads are an
important link in moving nutrients and energy between marine and terrestrial
ecosystems. Using their figures for loggerhead nests, Frazer (2001) speculated on
the magnitude of materials moved onto Caribbean beaches prior to the reduction
of green turtle populations by European colonization of the New World. Using an
estimate of 34,000,000 adult green turtles in the pre-Columbian Caribbean (see
Jackson, 1997; Bjorndal et al., 2000) and assuming that half of them were females,
Frazer (2001) estimated that they would make 23,800,000 nests per year (4.2 nests
per female with a 3-year average remigration interval). That would have resulted
in a contribution of some 1,600,000 kg of organic matter, 365,000 kg of lipids,
170,000 kg of nitrogen, 15,500 kg of phosphorus, and 44,500,000,000 kJ of energy
to Caribbean beaches each year. Actual figures may have been higher, because
green turtles tend to lay their eggs higher up on the beach than do loggerheads
(Bouchard and Bjorndal, 2000). One can only wonder at the likely results and
impact of greatly curtailing these previous levels of annual inputs into terrestrial
systems.
Such speculation is an interesting pastime but does not really provide useful
information in determining how many turtles we need. How many nesting turtles
does it take to maintain a healthy level of nutrients on a beach? How many hawksbills
are necessary for the proper maintenance of a productive coral reef (Meylan, 1988;
see also Chapter 10, this volume)? How many green turtles are needed per hectare
of seagrass bed to sustain optimal productivity of such systems? Although we
admittedly do not know with any accuracy how many sea turtles of each species are
necessary to restore or sustain their prehistorical ecological and ecosystem function,
it is likely that it will require populations or meta-populations on the order of 10 4 –10 7 .
However, if we desire these population levels, it may also be necessary to restore
seagrass beds and coral reefs to their former levels of extent prior to human influences
in order to support prehistorical numbers of turtles (Jackson 1997; Bjorndal et al.,
2000). Such an undertaking is practically impossible; it would require the re-development or restoration of coastal habitats throughout the planet and displace millions
of humans from their homes and livelihoods.
1123 book.book Page 375 Monday, November 11, 2002 11:11 AM