Australasian Science: Australia's authority on science since 1938

Over-Harvesting Recorded in Turtle DNA

By Stephen Luntz

The effects of over-harvesting are visible in the DNA of turtles decades after the exploitation stopped.

Olive ridley turtles were once common on the Pacific coast of Mexico, but between 1960 and 1990 more than two million were consumed for food before the practice was banned. In 1968 alone, 350,000 were taken.

The consequence has been a change in turtle behaviour. “Females no longer nest in synchronised masses with other females. Instead, they now seek a solitary nest,” says Jimena Rodriguez-Zarate, a PhD student in the Molecular Ecology Laboratory at Flinders University.

Rodriguez-Zarate explored the genetic effects on the turtle population, examining samples from 334 individuals at 18 sites spread across 3000 km. “The intensive exploitation of a few nesting sites caused a reduction in genetic diversity in olive ridley turtles along the entire coastal region,” she says, even though numbers are reviving.

Sea turtles return to the beach where they were born to lay their eggs, and so far there has been no re-colonisation of Mismaloya Beach, a major commercial centre for the turtle trade, even though it is now in a national park. Consequently the population at Mismaloya Beach has become genetically distinct from those elsewhere as all the turtles there are the products of a small group of survivors.

“The results serve as a guide to where to set up marine reserves,” says Prof Luciano Beheregaray, Rodriguez-Zarate’s supervisor. Rodriguez-Zarate says that the work proves that it is not enough to protect a species at a few key locations. If the genetic diversity is to be conserved, populations at many locations need to be considered.

A recent American study used similar techniques to reveal evidence of slavery and genocide in the DNA of people of Caribbean ancestry.