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OCR for page 144
8
Conclusions and
Recommenc/ations
CONCLUSIONS
he committee has analyzed available data on the five sea turtle
species found in U.S. territorial waters to ascertain current popula-
tion trends. The most important data were the numbers of nests or
nesting females on the nesting beaches, but other useful data were
the incidences of turtle strandings and numbers of adults sighted at
sea in the course of aerial surveys.
Population trends of several species were evident especially from
counts of nests and nesting females. The Kemp's ridleys on the nesting
beach at Rancho Nuevo, Mexico, have declined to about 1% of their
abundance in 1947; since 1978, the number of nesting females has
declined from about 700 to an estimated low of only 350 in 1989. This
species is obviously the most critically endangered of all the sea turtle
species. Counts of loggerheads nesting on various beaches of the south-
eastern coasts vary with latitude: numbers of nesting loggerheads on
South Carolina and Georgia beaches are declining; but in two study areas
in Florida, the numbers seem to be stable in one and appear to be
increasing in the other. Green turtles are showing some increased nesting
on Hutchinson Island, Florida. Leatherbacks and hawksbills nest too
infrequently on southeast beaches for clear-cut trends to be identified.
144
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145
Conclusions and Recommendations
As judged from stranding data, the most abundant turtles in U.S.
coastal waters are loggerheads; Kemp's ridleys and green turtles are less
abundant; and leatherbacks and hawksbills are even less common. Aerial
surveys designed to count turtles at sea have yielded less precise num-
bers, because many adult turtles and small juveniles are difficult to identi-
fy and count accurately from the air. As a result, aerial surveys have been
used only sparingly to assess patterns of sea turtle distribution; their
results, however, support the belief that loggerheads are the most abun-
dant species in both inshore and offshore habitats.
Causes of sea turtle deaths, and especially causes associated with
declining populations, can be categorized either as natural or related to
human activities. Sea turtles have long been harvested for their eggs and
meat, for their shells (carved for ornaments), and for their skin (leather)
and various body parts (oil-based derivatives). Overexploitation of green
turtles for a turtle cannery industry in the Gulf of Mexico as early as the
late 1800s was largely responsible for their decline in the early 1900s.
A wide range of human activities have been identified as causing sea
turtle deaths. Those with effects especially on sea turtle eggs and hatch-
lings include various beach manipulations (e.g., fortification, deposition
of sand, cleaning), the use of artificial lighting, vehicular and human traf-
fic on beaches, and the planting of exotic vegetation. Although mortality
data on many of those factors have been found for various sites at vari-
ous times, the data are generally too sparse and localized for use in quan-
tifying long-term effects on sea turtle species. The committee was better
able to quantify human-associated causes of deaths of juvenile and adult
sea turtles.
Of all the known factors, by far the most important source of deaths
was the incidental capture of turtles (especially loggerheads and Kemp's
ridleys) in shrimp trawling. This factor acts on the life stages with the
greatest reproductive value for the recovery of sea turtle populations.
Strong evidence for the effect of shrimp trawling on turtles came from the
following findings:
· The mortality of turtles caught in shrimp trawls increases markedly
for tow times greater than 60 minutes.
· Numbers of stranded turtles increase with the opening of shrimp
seasons and decrease with the closing of shrimp seasons.
· Loggerhead populations declined in areas where shrimp trawling off
their nesting beaches was intense, but did not decline in areas
where trawling was not intense.
· The estimated numbers of sea turtles captured by shrimp trawling
are large.
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146
Decline of the Sea Turtles
Other fishery operations, lost fishing gear, and marine debris are
known to kill sea turtles, but the reported deaths are only about -~0% of
those caused by shrimp trawling. Dredging, entrainment in power-plant
intake pipes, collisions with boats, and the effects of petroleum-platform
removal all are potentially and locally serious causes of sea turtle deaths.
However, these collectively amount to less than 5% of the mortality
caused by shrimp trawling. Natural diseases and parasites, and toxic sub-
stances can and do kill sea turtles, but their overall effects on sea turtle
populations cannot be quantified. Sea turtles commonly ingest a wide
variety of plastic substances and petroleum residues that can harm them.
Although the ingestion of plastics has been observed, the magnitude of
resulting mortality cannot be determined from existing information.
Natural predation on turtles in all life stages, parasitism, diseases,
inclement weather, beach erosion and accretion, thermal stress, and high
tides are all known to affect populations adversely, especially on the nest-
ing beaches. But the committee concluded that changes in natural
sources of mortality are not the causes of observed population declines
except in a few localized instances.
Thus, the committee identified population declines in sea turtle popu-
lations, and it determined that the most important mortality factor has
been the incidental capture of subadult and adult sea turtles in shrimp
trawls.
RECOMMENDATIOINIS
Conservafion Measures
The committee considered several options for conserving sea turtles.
Rather than recommend specific regulations, the committee has focused
on various aspects of sea turtle biology and various sources of mortality.
Its recommendations are therefore general enough to permit various man-
agement options in some cases. However, it is clear to the committee
that at least the Kemp's ridley population is dangerously small and that
the species needs increased protection. In addition, loggerheads are
declining rapidly in South Carolina and Georgia, and green turtles remain
uncommon, although they are beginning to show some evidence of pop-
ulation increase at one site in southern Florida. All of those species need
increased protection under the Endangered Species Act and other relevant
legislation.
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147
Conclusions and Recommendations
Reducing Incidental Deaths of Juvenile and Adult Sea Turtles
Shrimping Incidental deaths due to shrimping must be reduced. An
estimated 5,500-55,000 loggerheads and Kemp's ridleys are killed each
year by shrimping activities in U.S. waters. The waters off northern Flori-
da, Georgia, South Carolina, Louisiana, Mississippi, Alabama, and Texas
are most critical, but the committee recommends the use of TEDs in bot-
tom trawls at most places and most times of the year from Cape Hatteras
to the Texas-Mexico border. At the few places and times where TEOs
might be ineffective (e.g., where there is a great deal of debris), alterna-
tive conservation measures for shrimp trawling might include tow-time
regulations under very specific controls and area and time closures.
Restrictions could be relaxed where turtles are and historically have been
rare, such as in deeper waters of the gulf.
The committee believes that shrimping with adequate controls is com-
patible with the recovery of turtle populations. Although prohibition of
shrimp trawling might be required as a "last-ditch" measure under the
Endangered Species Act, appropriate application of existing technolo-
gy-especially TEDs, innovative new technologies, and other conserva-
tion measures have the potential to reduce sea turtle mortality to a level
that the populations can tolerate. The committee comments here on
some of the available controls.
· TEDs. The use of TEDs at all times in all areas could theoretically
reduce the capture of sea turtles to 3% of the rate seen without
TEDs. However, complicating factors, such as the presence of sea-
grasses and other debris, reduce the fishing effectiveness of TED-
equipped trawls at some times and might even prevent the success-
ful ejection of turtles that enter the trawls. The available data do not
show conclusively that significant numbers of sea turtles occupy all
waters fished by shrimpers throughout the entire year. However,
turtles are present in some areas even where TEDs are not now
required. For example, current regulations do not require TED use
from northern Florida to Cape Hatteras waters after the end of
August, but stranding data and aerial-survey data demonstrate that
sea turtles, especially Kemp's ridleys, are in fact still in these waters
through December and are suffering trawl-related mortality.
Tow-time limits. Available data suggest that limiting tow durations
to 40 minutes in summer and 60 minutes in winter would yield sea
turtle survival rates that approximate those required for the approval
of a new TED design. Use of tow-time restrictions would avoid the
clogging problems experienced when TEDs are used in areas with
abundant debris. The 1987 NMFS regulations appropriately incorpo
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Decline of the Sea Turtles
rated tow-time limits as an option in inshore waters, where there
often is much debris. However, these tow-time regulations need fur-
ther refinement. Current tow-time limits are too long, if animals
described as comatose in prior reports were in fact destined to die.
Also, the current tow-time limits are not properly stratified by season
to protect turtles adequately in warm seasons.
· Relaxation of TED use and tow-time regulations at selected
locations and times. TED use and tow-time limits might be selec-
tively applied when and where the probability of capturing sea tur-
tles does not exceed acceptable levels. Available information should
be examined for the potential of such fine tuning. Because the over-
lap between turtle distribution and fishing activities is great, such an
approach would have limited applicability, but would perhaps make
the regulations less onerous.
· Limited time/area closure for turtle "hot spots." Under special
circumstances (e.g., in waters adjacent to dense nesting beaches),
sea turtle concentrations in defined areas might be temporarily so
high, or the turtles so vulnerable, that other conservation measures
do not offer adequate protection.
Other Human Activities Sea turtle deaths incidental to other human
activities such as operation of other fisheries, abandonment of fishing
gear, dredging, and oil-rig removal-should be addressed and reduced.
Finfish trawls kill some turtles. Groundfish trawls are structurally and
operationally similar to shrimp trawls, and their potential effects on sea
turtles that encounter them are similar as well. Observer data on rates of
sea turtle capture and deaths related to groundfish trawls are not available.
The committee recognizes the need for NMFS to assess the effects of gill-
net fisheries and the winter groundfish trawl industry on the incidence of
turtle capture and mortality. If mortality is substantial, NMFS should con-
sider expanding the regulations designed to protect sea turtles from
drowning in trawl nets to include all bottom trawls and set nets, not only
shrimp trawls. That would protect sea turtles now at risk because of win-
ter groundfish trawling and the setting of unattended nets, such as pound
nets and gill nets.
Research and development should continue, in an effort to reduce fur-
ther the loss of sea turtles in hopper dredges. Modification of dragheads
to exclude turtles during maintenance dredging appears to be feasible,
and research on modifications continues. Continuing surveys of popula-
tion numbers and movements within important, frequently dredged
entrance channels will provide more understanding of sea turtle behavior
that will be applied to improving management designs. Turtles should be
relocated away from dredging operations when necessary.
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Conclusions and Recommendations
The observer program is essential to measure the success of efforts to
mitigate the loss of sea turtles in hopper dredges. Finding turtle carcasses
or remains in the hopper sediments is difficult, so the on-board observer
program should be continued. Although some preliminary work has
been done, hopper dredges must be monitored, especially where sea tur-
tles might be involved.
Other sources of turtle mortality should be reduced. Marine debris and
pollutants can kill turtles that ingest them. MARPOL and other programs
to reduce marine pollution are in place, and some have recently been
strengthened. Sea turtles are affected to some degree by explosions asso-
ciated with the building and demolition of marine structures, especially
those related to the oil and gas industry. MMS and NMFS programs are
under way to reduce these potential impacts.
Reducing Directed Harvest of Sea Turtles
Directed harvest of all sea turtle species in U.S. waters should continue
to be prohibited. Because of the transnational migration and distribution
of sea turtles, population recovery would be substantially improved if all
directed harvests of sea turtles were eliminated in other countries as well.
Reproduction-Relatec! Protection
Critical nesting areas, nesting activities, and early life stages (eggs and
hatchlings) of each species must be protected. Areas of particular con-
cern include beaches between Melbourne Beach and Wabasso Beach,
Florida, for loggerheads and the Rancho Nuevo beach in Mexico for
Kemp's ridleys. Protection of nesting areas, nesting activities, and eggs
and hatchlings is critical to the survival of the Kemp's ridley, and its
importance for other species is increasing, in light of continued beach
development, land use patterns, and other beach practices. Possible
actions include public purchase of undeveloped beaches for restricted,
nonthreatening uses; public purchase of development rights for undevel-
oped beaches; prohibition of vehicular traffic on beaches during nesting
and incubation periods; control of lighting in the vicinity of nesting
beaches; predator control; and establishment of a marine park at Rancho
Nuevo. The 16 km of undeveloped beach property between Melbourne
Beach and Wabasso Beach, Florida, in the Archie Carr National Wildlife
Refuge proposed by the U.S. Fish and Wildlife Service, should be protect-
ed. Purchase of the land is the best method to ensure protection. The
lands are available, and action should be taken before they are developed.
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Decline of the Sea Turtles
Small-scale, research-based captive breeding programs for Kemp's rid-
leys should be continued. Refinement of the technique would ensure the
maintenance of a gene pool in captive animals in the event of a population
loss. However, this option is not considered a promising management tool
for the restoration of wild populations, because small populations of cap-
tive animals lack much of the genetic variability that was available in the
wild population. In addition, the development of various survival behav-
iors, for example, feeding, nesting, and migration, might be impaired.
Headstarting should be maintained as a research tool, but cannot substi-
tute for other essential conservation measures. The headstarting experi
ment should be continued, because it has research and public-awareness
value. Experimental methods must continue to be improved. However,
present knowledge makes it clear that headstarting, even if it works, will
not be effective without simultaneous implementation of other conservation
measures to reduce human-related deaths of juvenile and adult sea turtles.
Research
Sea Turtle Biology
In the process of evaluating the status of sea turtles, some knowledge
gaps became apparent. Important data are missing some difficult (or
impossible) to obtain, some less so-that are imperative to good manage-
ment. Current knowledge of sea turtles has allowed us to evaluate and
recommend some basic research and conservation measures in this report
so that further protection and recovery of sea turtle populations can be
implemented.
Demographic Models For no species of sea turtle is knowledge of age-
specific survivorship and age-specific fecundity adequate. Enough is
known, however, about loggerhead demography to provide a fundamen-
tal understanding of basic concepts, such as the relative reproductive
value of various life history stages. To evaluate fully the comparative
importance of different sources of mortality and to evaluate the effective-
ness of conservation measures, better information is needed on age at
reproductive maturity, age-specific survivorship, age-specific fecundity,
and their variances. Therefore, the committee recommends research on:
· Age-specific fecundity and survivorship, through enlargement of
existing tagging programs and creation of new ones; special atten-
tion must be given to the tag-loss problem.
· Life stages and sex ratios, through increased efforts to count sea tur-
tles of all age groups in as many habitats as possible; mortality esti-
mates for all life stages are important.
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Conclusions and Recommendations
Sec Turtle Distribution Information is needed on foraging habitats of
sea turtles in deep water and the use of shallow water by juveniles and
subadults. Sampling areas and times should be chosen to permit replica-
tion with the best current technology. Such surveys should help to define
the amount of overlap of national jurisdictions and assist the implementa-
tion of cooperative programs, such as that between the United States and
Mexico for the Kemp's ridley.
Sec Turtle Physiology and Pathology More information is needed on
the effects on turtles of ingesting plastics, of petroleum products, of
forced prolonged immersion, of cold-water stunning, of underwater
explosions, and of oceanic debris. The committee recommends selected,
complete necropsies to determine pathological conditions, causes of
wounds, and any other cause of death. Research should also ascertain
turtles' abilities to ingest plastics of various types and sizes without
adverse effect. The effects of floating petroleum products on the repro-
ductive and feeding behavior of turtles should be studied.
To allow for the complete evaluation of the use of tow-time limits in
trawl fisheries, research should address how enforced submergence
affects sea turtle anatomy and physiology as a function of season, water
temperature, species and size, time of day, and history of previous forced
submergence. Improved resuscitation techniques of comatose turtles
should be developed from such research.
The effect of explosives on sea turtles during construction and demoli-
tion of marine structures or for any other reason (such as military ord-
nance) is largely unknown and must be investigated. Research should
focus on the distribution and abundance of sea turtles near platforms des-
ignated for removal by explosives, confirmation and necropsy of dead
turtles near explosion sites, the feasibility of moving turtles to different
sites, and behavior of animals at explosion sites.
Research on the reproductive biology of sea turtles in the wild should
continue.
Management Techniques
More research and experimentation are needed to improve TEDs and
explore new alternatives. The techniques of deploying TEDs in a variety
of conditions also need improvement. For example, it is important to
reduce the tearing of trawl nets that have TEDs. If TEDs can be modified
to allow efficient fishing for shrimp when seagrass and other algal detritus
or other debris are abundant, a major objection to the use of TEDs by
shrimp fishermen could be addressed. All these management techniques
and options should include input from shrimp fishermen and gear
experts. Enhancing acceptance of regulations on the shrimp fishing
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Decline of the Sea Turtles
industry would enhance compliance and promote sea turtle conservation,
and research should focus on whether education on TED use would be
helpful in this regard. Research should also address other inducements to
increase compliance with TED regulations.
There are strong grounds for believing that the drowning of sea turtles
in trawls can be greatly reduced by the adoption of certain controls on
the shrimp fishery, but it is important to evaluate the effectiveness of any
regulations that are adopted. Because the shrimp fisheries are regulated
to open and close at various specified dates at many places, the commit-
tee was able to use the timing of the fishery to test the impact of shrimp
trawling on the numbers of stranded sea turtles.
This test produced strong evidence that shrimp trawling at some places
and times is responsible for 70-80% of the sea turtles found stranded on
the beaches of Texas and South Carolina. In contrast, the committee was
not able to develop similar tests of the degree to which plastic debris, oil
pollution, and other factors affect the survival of sea turtles.
The characteristics of the shrimp fishery that helped identify its effect
on turtles should be used to test the effectiveness of the regulations. His-
torical data on the relationship of the numbers of stranded sea turtles to
the opening and closing of the shrimp fishery in Texas and South Caroli-
na should be collected in future years to evaluate the degree to which the
drowning of sea turtles in trawls is reduced by the regulations.
Further research is necessary to assess the effectiveness of tow-time
limitations. For example, are shrimp trawlers ever so concentrated that
they repeatedly catch individual sea turtles often enough to make tow-
time limits ineffective? Even though sea turtles can survive enforced sub-
mergence for some time, repeated submergence can cause drowning.
Shrimp trawlers could help to answer the question by using carapace
marks to denote captures and recaptures and then assessing turtle survival
as a function of capture frequency during relatively short periods (e.g., a
day). The results of the physiological research described above would
also help.
The impact of fishing practices other than shrimp trawling on sea tur-
tles might be large, but it is not well known. Research is needed on the
impact of groundfish trawling, set-net and long-line fishing, gill nets, and
pound-net fishing on sea turtles at different times and places.
Research on the complex effects of artificial protection of early life
stages of sea turtles is needed. Special efforts should be directed to
reproductive biology of captive sea turtles and the effects of rearing them
in closed culture. Young turtles just out of captivity might not be pre-
pared to survive in the wild. Research on means of acclimation of nurs-
ery-reared sea turtles would be profitable. How long should sea turtles
be reared in captivity to maximize their ultimate survival in the wild? Is it
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153
Conclusions and Recommendations
worth taking an egg from a beach to raise the turtle in the nursery? It is
not known whether female sea turtles are imprinted to nest on the beach
where they were released. That information is needed before the place
of release of nursery-reared turtles is determined.
The cumulative effects of human activities on nesting beaches should
be quantified relative to the total available nesting areas, because the loss
of nesting beaches through development or alteration could extirpate
local populations. More research is needed on how to control or alter
artificial lighting along nesting beaches, to minimize interference with
nesting and with the crawl to the sea by emerging hatchlings. The
impacts of motor vehicles on beaches, erosion control measures, and the
development of beachfront property needs to be evaluated more com-
pletely.
Representative terms from entire chapter:
sea turtle
