Decline of the Sea Turtles Causes and Prevention (1990) / Chapter Skim
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2. Biology
2. Biology
Pages 21-41
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From page 21... ...
Historically, all sea turtles have been valuable to humans. The leatherback, although widely reputed to be inedible, is killed extensively 21
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22 Decline of the Sea Turtles FIGURE 2-1 Sea turtles found in U.S. coastal waters.
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From page 23... ...
This chapter describes five of the eight species of sea turtles (Figure 21) each in terms of its distribution, its population and habitats, its food habits, its reproduction and growth, and major threats to its survival.
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From page 24... ...
Adults are found almost entirely in the Gulf of Mexico, where tag returns from cooperative shrimp fishermen from the United States and Mexico suggest an approximately equal distribution between the northern gulf and the southern gulf (Pritchard and Marquez M., 1973; Marquez M., in prep.~. Satellite-tracked females migrating north and south of the nesting beach at Rancho Nuevo remained in nearshore waters less than 50 m deep and spent less than an hour each day at the surface (Bytes, 1989)
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From page 25... ...
believed that loggerheads and Kemp's ridleys partitioned food resources in Texas: the ridleys forage in shallower water and take the relatively fast blue and spotted crabs, whereas loggerheads are in deeper water and feed on slow-moving crabs. Marine areas within several kilometers of the nesting beach at Rancho Nuevo, Mexico, constitute important internesting habitat for Kemp's ridleys.
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From page 26... ...
First, it nests in an aggregated fashion; many females gather in the sea near the nesting beach and then emerge to nest in a loosely synchronized manner over several hours in what is known as an "arribada" or "arribazon" pattern. An important amateur movie made by Andres Herrera in 1947 documented an arribada of approximately 40,000 females nesting on one day at the Rancho Nuevo beach (Carr, 1963; Hildebrand, 19639.
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From page 27... ...
With the limited data available, the number of adult females in the world population can be estimated from the equation: Pnf = ~ - Pnf Nf where Pnf = Nt Nf Pnf = total population of adult females total number of nests per year average number of nests per reproductively active female proportion of females that nest in a given year Observers who have worked closely with Kemp's ridleys argue that the actual number of nests per year per female is not 1.3, as suggested by Marquez M
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From page 28... ...
Major Threats to Survival At various stages of their life cycle, Kemp's ridleys can be adversely affected by a number of activities and substances. These potentially include cold-stunning; human and nonhuman predation of eggs in nests; predation of hatchlings and/or older turtles by crabs, birds, fish, and mammals, including humans from foreign nations; ingestion of plastics; industrial pollutants; diseases; exploratory oil and gas drilling; dredging; explosive removal of oil platforms; and incidental capture in shrimping and other fishing gear.
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From page 29... ...
, published life tables and population models (Richardson and Richardson, 1982; Frazer, 1983b; Crouse et al., 1987) , observed mortality rates in the southeastern United States, and observed population declines in South Carolina (pers.
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From page 30... ...
Reproduction and Growth It has been assumed for some time that, at least for Florida loggerheads, males migrate with females from distant foraging areas to the waters off nesting beaches, where courtship and mating take place. Mating takes place in late March to early June (Caldwell, 1959; Caldwell et al., 1959a; Fritts et al., 19831.
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From page 31... ...
In the southeastern United States adult females begin to nest as early as the last week of April; nesting reaches a peak in June and July and continues until early September. Loggerheads nest one to seven times per season (Talbert et al., 1980; Lenarz et al., 1981; Richardson and Richardson, 19821; the mean is believed to be approximately 4.1 (Murphy and Hopkins, 19841.
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From page 32... ...
. Characteristics that distinguish them from other sea turtles are their small rounded head, smooth carapace, and four pairs of costar scutes.
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From page 33... ...
The foraging habitats are most commonly pastures of seagrasses or algae, but small green turtles are also found over coral reefs, worm reefs, and rocky bottoms. Some feeding grounds support only particular size classes of green turtles; the turtles apparently move among these developmental feeding grounds.
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From page 34... ...
Reproduction and Growth Green turtles mate in the water off the nesting beaches. Evidence is accumulating that males might migrate to the nesting beach every year (Balazs, 19831.
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From page 35... ...
Major Threats to Survival Over much of its range, the green turtle has been severely depleted because of high demand for both eggs and meat as human food. Exploitation has been intense on both nesting beaches and foraging grounds, and cannot be reversed quickly, because the green turtle takes several decades to reach maturity.
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From page 36... ...
Hawksbills might be much more sedentary than other members of the family Cheloniidae (Witzell, 1983) , but long-range tag returns indicate that hawksbills can move hundreds of kilometers between their nesting beaches and foraging areas (Nietschmann, 1981; Parmenter, 1983; Bjorndal et al., 19851.
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From page 37... ...
Some active nesting beaches have no exposed sand, but have woody vegetation growing to the water's edge. In contrast, hawksbills at Sandy Point, St.
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From page 38... ...
Adult females can make their first appearance at a nesting beach any time from.June to September. If a population contains only a few animals, females that use a particular nesting beach might arrive rather irregularly, causing the apparent nesting season to vary widely from year to year.
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From page 39... ...
In some parts of its range, especially in the Indian Ocean, an occasional hawksbill is highly poisonous. LEATHERBACK General Description The leatherback is the largest of all living sea turtles, attaining a length of 150-170 cm SCL and a weight that occasionally reaches 500 kg (rarely 900 kg)
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From page 40... ...
A few nests are recorded each year on many of the islands of the Caribbean. Leatherback nesting beaches have some common characteristics.
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From page 41... ...
Hatching success can approach 100% in an undisturbed natural nest, but on many beaches many eggs are lost to erosion a result of the high energy of the beaches favored by leatherbacks and the limited ability of such heavy and cumbersome animals to travel far inland to deposit their eggs. Eggs can be transferred to hatcheries, but they need even more careful handling than those of other sea turtles, if viability is to be maintained during the transfer.
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