Life history traits of sea turtles and their application to conservation efforts (outline)

This topic submitted by Nick Teets ( teetsnm@miamioh.edu) at 8:18 PM on 3/27/06.

Tara and Scott SCUBA along the Wall at Runway Ten, 15 m deep, San Salvador, Bahamas.

Tropical Field Courses -Western Program-Miami University


I will be talking about life history patterns in sea turtles, and how knowledge of sea turtle life history can be used to improve conservation efforts. In particular, I will talk about sea turtle reproduction, sex determination, juvenile behavior, and growth rate. Sea turtle habitat selection and nesting site selection are influenced by many variables, and scientists have just recently begun to understand these variables. Subsequently, I will relate each of the above life history traits to current conservation efforts, and how this knowledge will change future conservtaion strategies. All current species of sea turtles are either on the "endangered" or "critically endangered" list, but so far conservation efforts have had resounding success in rebounding sea turtle numbers. However, in the United States numbers are still well-below their pre-Columbian levels, so improved conservation tactics are still needed.

I. Introduction
A. Sea turtles are members of the family cheloniidae
B. Range
1. Sea turtles are found in every ocean except the Arctic Ocean
C. Habitat
1. Sea turtles live primarily in shallow, coastal waters, bays, and estuaries.
a. Spend first 30 years of life maturing in ocean, then return to shore to
nest.
b. Some species of sea turtles migrate extensively, primarily between nesting
grounds and feeding sites.
D. All species of sea turtles are endangered, primarily for the following reasons:
1. Historically, sea turtles have been hunted extensively for their meat and
shells, and eggs were also consumed by coastal peoples.
2. Biggest current threat is long-line fishing, which kills approximately 40,000
individuals per year.
3. Overdevelopment of beach nesting sites is also a threat to sea turtle eggs and
hatchlings.

II. Reproduction and Sex Determination in Sea Turtles
A. Most sea turtles show a high degree in selectivity for a nest site.
1. Many sea turtles return to the general region they were born to reproduce.
2. Sea turtles also show a high degree of accuracy in returning to previous nesting
grounds.
B Sea turtles also use many other cues to select a nesting site, including:
1. Marine factors, such as:
a. Olfactory cues
b. Surf noise
c. Magnetic fields
d. Offshore currents
e. The presence of reefs and rocks
2. Terrestrial factors
a. Beach slope and width
b. Sand texture
c. Dune vegetation
d. Interspecific competition
e. Predation
f. Human activities, such as artificial lighting
C. Overall, sea turtle nesting patterns show a non-random distribution.
D. Sea turtles tend to lay large numbers of eggs by reptilian standards
1. Can lay roughly 50-200 eggs per clutch, and up to 6-7 clutches per breeding
season
2. However, sea turtles usually do not breed every year.
E. Sea turtles, like many reptiles, show temperature-dependent sex determination (TSD)
1. Higher temperatures yield females, while lower temperatures yield males
a. The pivotal temperature for most species is about 29° C.

III. Sea turtle habitat and behavior as a juvenile
A. Hatching is governed by photoperiod, and upon hatching, sea turtles use magnetic cues
to orient and navigate themselves.
B. Typically, sea turtles spend the first 3-5 years of their life in the open ocean, after
which they migrate to shallow coastal areas to feed and mature.
1. Juvenile sea turtles inhabit a narrow home range, which consists of a foraging
area and a nocturnal resting site.
a. Both the foraging and resting sites are typically found in nearshore
reefs, where there is no sand
b. The foraging areas of individual turtles show some overlap, while the
nocturnal resting sites tend to be specific for each individual turtle and
aren’t shared.


IV. Growth rates of sea turtles
A. Straight carapace length (SCL) is a good predictor of sea turtle growth rates
1. Sex, habitat site, mean size, and year can also affect growth rate.
B. Turtle growth rates are density dependent, that is, growth rate and population density
are inversely related.
1. The main cause of this density-dependent growth rate is nutrient limitations.
2. Sea turtles’ diets primarily consist of the seagrass Thalassia testudinum, so
its population density is a good indicator of sea turtle carrying capacity.
C. Sea turtles on the Atlantic coast have higher growth rates than those on the
Pacific coast

V. Relationship between sea turtle life history and conservation efforts
A. An understanding of sea turtle life history is essential to select the most efficient
conservation strategy to aid the recovery of global sea turtle populations.
1. An analysis of sea turtle nesting sites has allowed conservationists to protect
common nesting grounds and even rebury nests at central hatching locations.
2. Information on sea turtle TSD has allowed researchers to adjust sex rations by
moving nests to different sites.
3. A better understanding of juvenile sea turtles’ dependence on photoperiod for
hatching has resulted in the removal of artificial lights from sea turtle nesting
sites.
4. Because of the dependence on magnetic field for orientation, the use of wire
fences to protect fences is being reevaluated, as these may alter the magnetic
field around the nest.
5. An understanding of sea turtle home ranges and foraging grounds can be used to
protect young sea turtles.
6. Knowledge of sea turtle growth rates and carrying capacity can be used to
create ideal growth conditions for endangered populations.

References
Makowski C, Seminoff JA, Salmon M. 2006. Home range and habitat use of juvenile Atlantic green turtles (Chelonia mydas L.) on shallow reef habitats in Palm Beach, Florida, USA. Marine Biology 148:1167–1179.

Bjorndal KA, Bolten AB, Chaloupka MY. 2000. Green turtle somatic growth model: evidence for density dependence. Ecological Applications 10:269-282.

Weishampel JF, Bagley DA, Ehrhart LM, Rodenbeck BL. 2002. Spatiotemporal patterns of annual sea turtle nesting behaviors along an East Central Florida beach. Biological Conservation 110:295–303.

Broderick AC, Frauenstein R, Glen F, Hays GC, Jackson AL, Pelembe T, Ruxton GD, Godley BJ. 2006. Are green turtles globally endangered? Global Ecology and Biogeography15:21–26.

Davenport J. 1997. Temperature and the life history strategies of sea turtles. J. therm. Biol. 22: 479-488.

Baskale E, Kaska Y. 2005. Sea turtle nest conservation techniques on southwestern beaches in Turkey. Israel Journal of Zoology 51:13–26.

Irwin WP, Horner AJ, Lohmann KJ. Magnetic field distortions produced by protective cages around sea turtle nests: unintended consequences for orientation and navigation? 2004. Biological Conservation 118:117–120.


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