Management Research Needs 



Natural Mortality in Sea Turtles; Obstacle or 

 Opportunity? (Nicholas Mrosovsky) 



Qualitative Observations 



Turtles are subject to natural mortality from the moment the 

 eggs are laid, sometimes even while the eggs are laid, as when 

 raccoons sneak up behind nesting loggerheads, or when 

 leatherbacks lay so close to the surf that the eggs fall with a 

 splash into water at the bottom of the hole. Later crabs and 

 various mammals dig up the eggs (Schulz 1975) and flies crawl in 

 and lay their eggs on the broken turtle eggs; mould spreads and 

 many eggs rot (Cornelius 1986) . Roots invade nests dug too far 

 up on the beach: high tides inundate nests dug too low. Rain- 

 compacted soil prevents hatchlings from emerging. In other cases 

 emergence is possible but, nevertheless, hatchlings die in the 

 nest (Whitmore and Button 1985). When many females lay on the 

 same beach, they dig up each other's nests. After emergence 

 birds snatch up the hatchlings enroute to the sea, especially 

 when emergence is by day (Mrosovsky 1971; Fretey and Lescure 

 1981) . Once in the water, fish take their toll. Sharks also prey 

 on the larger turtles (Balazs 1979) . Even full grown 

 leatherbacks can be eaten by killer whales (Caldwell and Caldwell 

 1969) . On shore jaguar and puma take adults (Schulz 1975; 

 Cornelius 1986) . Other turtles become stuck in tangles of 

 branches or wander inland and die of heat stress when the sun 

 comes up the next day (Fretey 1977) . Large numbers of green 

 turtles have been stranded on mud flats by cyclones (Limpus and 

 Reed 1985) . Lagoonal populations of greens and loggerheads are 

 stunned by cold during cold snaps (Mendonca and Ehrharc 1982) . 

 Stancyk's (1982) review gives many other references on predation, 

 but a monograph would be needed even to catalogue all the 

 predators and the abiotic factors contributing to natural 

 mortality of sea turtle species in different parts of the world, 

 and it would not be a particularly profitable exercise. 

 Observations on natural history are a useful start but what is 

 now needed is to progress beyond this initial stage to 

 quantification of the sources of mortality. Unfortunately, this 

 is hard to do. Nevertheless some examples of such attempts will 

 now be given to provide some orders of magnitude as starting 

 points, and to illustrate some of the problems in drawing any 

 general conclusions. 



Quantitative Studies 



Example 1; Ridlev arribadas at Nancite. Costa Rica 



A notable study of hatching success, or rather lack of 

 success, has been provided by Cornelius (1986) and his colleagues 

 for the arribadas of olive ridleys at Nancite, Costa Rica. The 



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