Research - Population structure

In addition to providing an index of relative abundance over time, the physical capture of animals affords opportunity to study population structure, which is perhaps the greatest and most unique attribute of in-water surveys. The parameters of greatest importance for studying population structure are the distribution of turtle size, the ratio of females to males, and assessment of natal origin using genetic markers. Because sea turtles are not sexually dimorphic and because physical appearance is not a reliable means for identifying individuals from different breeding populations, sex is determined by circulating testosterone levels and natal origin through DNA.

Sea turtles with similar color and characteristic
Twins? Guess again. Although these two sea turtles were only 0.1 cm different, both female, and captured at the same location within six hours of each other, they possess two very different genetic haplotypes.

Although some of this information could also be obtained from dead or moribund sea turtles that strand along the coast, because of the opportunistic nature of strandings it may not be possible to generate enough samples in some years or locations to facilitate comparisons. Furthermore, because of the often deteriorated condition of stranded turtles, size and sex data may be severely compromised. Lastly, there is at least some possibility of recapturing a previously measured sea turtle tagged and released during the in-water survey, providing possible future data on growth rates. Noteworthy demographic findings from various in-water trawling efforts managed by the SCDNR MRD in the last two decades include the observations that: