Decline of the Sea Turtles Causes and Prevention (1990) / Chapter Skim
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3. Population Trends
3. Population Trends
Pages 42-50
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From page 42... ...
The number of nests is an index that can be correlated with population size of mature females, rather than a direct~estimate, because sea turtles do not necessarily nest every year and because a female usually nests several times in a nesting season. But use of the index requires the fewest questionable assumptions about the biology of individual species of sea turtles.
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From page 43... ...
Numbers of nests and nesting females are assumed to generate comparable and useful data on all sea turtle species. KEMP'S RlDIEY In 1947, an estimated 40,000 female Kemp's ridleys were observed nesting during a single day at Rancho Nuevo (Carr, 1963; Hildebrand, 1963)
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From page 44... ...
.43, slope · -18.8, p · 0.02 3ooo 1 2600 t 2000 t 1600t 1000t Ann (c) Loggerhead N 160r 100 In 60 ~ o ' ' ' ' ' ' ' ' ' 1 ' ' ' ' ' ' ' ' ' 1 ' ' ' ' ' ' ' ' ' 1 19eO 1970 1980 1990 Little Cumberland Island, Georgia r 2 · .66, slope · -2.8, p · 0.0001 1 o 1970 1980 1990 Cape Island, South Carolina rue .65, slope · -119, p · 0.0001 (b)
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From page 45... ...
. 1960 Hutchinson Island, Florida (h)
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From page 46... ...
I I I ol i I ~ I t960 197O 19eO t990 t960 t970 1980 t990 Surinam Culebra, Puerto Rico r2. 0.0, elope -1.2, p · .43 r2.
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From page 47... ...
LOGGERHEAD Nesting loggerhead females on Little Cumberland Island exhibit a clear decline in numbers over 26 years (Figure 3-1O. The average decline of about 3% per year is not smooth, but the overall downward trend is unmistakable.
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From page 48... ...
The year-to-year variation is also apparent in green turtle nesting data from Surinam and Tortuguero, Costa Rica (Figure 3-li,p. The only other substantial regional nesting population, on Aves Island, Venezuela, has not been surveyed long enough for determination of trends, although qualitative observations during visits over many years suggest a heavy decline (Pritchard and Trebbau, 19841.
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From page 49... ...
SUMMARY The committee concluded that population trends are often challenging to interpret, and adequate surveys spanning 10 years or more are usually required to demonstrate with some certainty a change in absolute population numbers. However, much can be deduced about sea turtle trends from the studies of nesting densities to date.
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From page 50... ...
· Green turtle nestings on Florida beaches are low but are increasing at Hutchinson Island, Florida. · Hawksbill nesting is too sparse in U.S.
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