Sydney: Holiday makers love unspoilt beaches but their presence distresses turtles that are therefore unable to breed, a new study has found.

David Pike, doctoral student at the School of Biological Sciences, University of Sydney, has found that two turtle species - the loggerhead (Caretta caretta) and green turtle (Chelonia mydas) - produce more babies when nesting on beaches undisturbed by people or development.

Pike based his work on extensive scientific literature survey of articles published from 1900 to 2007 from around the world.

"Coastal ecosystems provide vital links between aquatic and terrestrial habitats, so they support extremely high levels of biodiversity," Pike said. "But, of course, we humans also love coastlines - they have the highest densities of human development anywhere on the planet."

"Beaches are a favoured destination for tourists, but are also a critical habitat for nesting sea turtles, so we have a situation where the potential for negative effects on these species is extremely high."

The data gathered on marine turtle reproductive output showed that female loggerhead and green turtles nesting on natural beaches produced more hatchling turtles per nest when compared to those nesting on beaches with permanent human development.

"Females who successfully produce more offspring will have higher lifetime reproductive success than females of the same species who produce fewer offspring.

"My study indicates that female marine turtles nesting on natural beaches are likely to have higher evolutionary fitness than female turtles nesting on developed beaches."

"This difference in the number of eggs that hatch has important implications for increasing the numbers of marine turtles that are out there."

"Over the last century numbers have plummetted because many fisheries practices accidentally capture and drown adult turtles. Protecting the remaining natural beaches may help build numbers in the coming decade."

Pike's study has been published in the UK Royal Society journal Biology Letters.