Lending a helping hand to gopher tortoises (Gopherus polyphemus) through head-starting may help augment depleted populations, according to new research.
“We know there are depleted populations in areas with suitable habitat,” said Daniel Quinn, who conducted the research as a graduate research assistant with the University of Georgia Savannah River Ecology Lab. He wanted to see if captive-rearing hatchling tortoises to a larger size could increase survival and thereby boost depleted populations in areas that have the resources they need.
He conducted his research at Georgia’s Yuchi Wildlife Management Area. The site provides ample habitat for the tortoises, Quinn said, but silviculture practices and illegal harvesting prior to the state purchasing the land likely reduced the population below a minimum viable size. Considered an imperiled species, the gopher tortoise is state listed in every state in which it occurs, he said, and is federally listed in some.
In the study published in the Journal of Wildlife Management, Quinn and his colleagues head-started and released 145 tortoises and radio-tracked 41 of them.
Collecting eggs from robust populations, the team hatched them in a lab and captive-reared the hatchlings for eight or nine months until they were about as big as two- or three-year-old gopher tortoises in the wild. They released the head-started tortoises at sites within Yuchi WMA that had ample space and suitable habitat. The researchers tracked the tortoises, looking at survival and movement.
“One concern with head-starting is that they won’t behave like the new site is their home, and they will start wandering off,” Quinn said. But these tortoises seemed to stay near their release site. Over the course of a year, none strayed farther than 122 meters.
Survival also proved to be successful when the team conducted “soft-releases” — putting the tortoises in outdoor pens at the field site before releasing them. At sites where the release methodology could be followed, survivorship was 70 percent annually, Quinn said, compared with a meta-analysis that concluded that hatchlings have 12.3 percent annual survival in the wild.
The research shows head-starting can help augment populations of gopher tortoises, Quinn said, but it won’t work by itself.
“It doesn’t fix problems that led to the decline in the first place,” he said. “Head-starting is a tool to augment a population once threats have been mitigated. Without addressing threats to survival, head-starting is unlikely to be effective. You have to mitigate or remove whatever was leading that population to decline in the first place.”
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