Another difficulty in using these data to assess natural 

 mortality is that although Tortuguero beach is protected, it is 

 not completely natural. Human predators could perhaps be 

 considered as natural, but the large number of accompanying dogs 

 do the most damage. The study area was near a village and may 

 not have been representative of the whole beach. 



Example 4; Loggerheads in South Carolina 



The fate of 458 loggerhead nests was determined for four 

 island beaches in South Carolina (Hopkins et al. 1978) . The 

 overall hatch rate of 6.1% was almost as low as for the Nancite 

 ridleys, but for very different reasons. Raccoons dug up 56% of 

 the nests in South Carolina (Table 3) . Losses to raccoons were 

 highest on the night the eggs were laid. Other interesting 

 details were that the chances of a nest being found by raccoons 

 did not depend on its location on the beach. Rather, raccoon 

 predation paralleled the density of nests. Such detailed studies 

 not just of predation levels but of the temporal and spatial 

 predisposing factors are helpful in controlling particular 

 threats. Indeed transplanting loggerhead clutches the night 

 they are laid greatly increases their chances of escaping 

 detection by raccoons (Stancyk et al. 1980). But, again, there 

 are difficulties in arriving at theoretical or practical 

 generalizations . 



Should raccoons be considered as natural predators? At Cape 

 Sable in the Everglades, predation by raccoons averaged 76% for 

 years in which no raccoons were removed (Davis and Whiting 1977) . 

 Despite these high levels Davis and Whiting (1977) considered 

 that predators of raccoons such as alligators, owls and bobcats 

 were sufficiently common and that the numerous raccoons were not 

 a result of human actions removing their predators. 

 Nevertheless, perhaps access to some turtle beaches has been made 

 easier for raccoons. The South Carolina beaches studied by 

 Hopkins et al. (1978), although relatively unspoiled, cannot be 

 considered completely natural. Water diversion schemes have 

 altered the erosion patterns, especially for Cape Island (note 

 17.9% egg loss, Table 3). 



The Hopkins et al. (1978) work brings out inter-beach 

 differences in a striking way. All the areas they studied were 

 relatively similar barrier islands, fairly close to each other, 

 yet large differences in the fate of nests were found, both in 

 losses to erosion and in type of predator. The low figures for 

 predation by raccoons for Sand Island may partly be because 

 people got to the eggs first on this relatively accessible beach. 

 This leads to consideration of an important point about the 

 interaction between the various factors contributing to 

 mortality. 



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