nor declining) . The upper curve is for a population that is 

 declining. 



For both populations, the figure tells us that an individual 

 of age 5 is not very valuable, whereas an individual of age 30 is 

 very valuable. A five-year old has little chance of surviving to 

 adulthood to reproduce. A thirty-year old has already survived 

 to adulthood and is reproducing. Hence, her value is greater. 

 Also, one egg is not very valuable. An egg has only one chance 

 in 1,000 of surviving to adulthood. 



Note how the value increases rapidly for older juveniles 

 just before they become adults, since they've already survived 

 the high juvenile mortality stage and are very likely to achieve 

 adulthood. 



The exact values upon which these models are based will 

 change as our knowledge of survival rates, fecundity, and age at 

 maturity improves, but the general shape of the curve is not 

 likely to change. For example, these models are based on an age 

 of maturity of about 23 years old. If it is actually younger 

 than that, the curves will shift to the left, but retain the same 

 shape. If the age is actually older, the curves would shift to 

 the right, but still retain the same shape. That is, older 

 turtles will still be much more valuable than younger turtles. 



These curves allow me to make certain recommendations 

 concerning management options for sea turtles. Let's assume for 

 the moment that we are absolutely determined to harvest this 

 resource. What does the slide tell us? It tells us that our 

 management options are limited. We clearly should harvest eggs 

 instead of turtles, since an individual egg is not very valuable 

 to the population. Of course, we would then want to reduce 

 natural mortality of eggs and also reduce any incidental take or 

 accidental destruction of eggs, so that we could maximize the 

 harvest and minimize the impact on the population. 



After all, even though an individual egg is not very 

 valuable to the population, turtles can come only from eggs, and 

 more eggs can come only from turtles, so we don't want to 

 overharvest in any case. Since turtles are "designed" for low 

 juvenile and egg survival, we might be able to take eggs without 

 destroying a population by substituting human predation for the 

 natural predation, with which the turtles have evolved to cope. 

 Also, due to environmental effects, there are those "doomed" eggs 

 that N. Mrosovsky keeps talking about — eggs that are laid in 

 places where they are in danger of being washed away by high 

 tides, etc. We might be able to take all "doomed" eggs, which 

 presumably represent "extra" eggs that would not become turtles 

 anyway. 



205 



