Environmental Engineering Reference
In-Depth Information
Box 5.1 Survival of Loggerhead Sea Turtles
Example of a longitudinal data set from a cohort of 100 loggerhead sea turtle
(Caretta caretta) eggs whose fate is followed over six stages of their life. The sur-
vival numbers can be used to calculate stage-specific survival rate (px) and to
graphically portray a survivorship curve. (Data from Crouse et al. 1987)
Age
Number
Number
Survival
Class x
Surviving Sx
Dying Dx
Rate px
Egg/hatchling
100
33
0.67
Small juvenile
67
26
0.62
Large juvenile
41
14
0.67
Subadult
27
8
0.70
Novice breeder
19
4
0.79
mature adult
15
3
0.80
the rest of their life in oceans prevents them from providing extended care
for their offspring. Thus, turtles produce many more offspring than one
would expect to survive and the newborn individuals must survive the mor-
tality gauntlet on their own. It is simply a numbers game.
If the strategy of dumping eggs and leaving them to their random fate
is an evolved strategy, then we must question whether or not protecting eggs
is indeed strategically the correct measure for sea turtle conservation. Be-
