Impact on predation of sea turtle nests when predator control was removed midway through the nesting season

Abstract

The beach at Hobe Sound National Wildlife Refuge (HSNWR) is a high-density nesting beach serving three species of threatened and endangered sea turtles. Historically, up to 95% of turtle nests at HSNWR were lost to predation by raccoons and armadillos. Consequently, predator control was identified as the most important conservation tool at HSNWR, and predator control optimised by predator monitoring led to highly successful results whereby predation had been reduced to low levels (7–13.5% of monitored nests) in 2002 and 2003. In 2004, funding shortfalls caused predator control to be curtailed with ~1.5–2 months remaining in the nesting/hatching season. We analysed the resulting effects on turtle nest predation levels compared with the results from 2002 and 2003. The predation rate in 2004 compared favourably with that of 2002 and 2003 until the end of June, after which control was curtailed. Thereafter, predation rapidly accelerated, with the 2004 predation rate increasing to 1.5–3 times the rates from 2002 and 2003 by the end of August. The discrepancy in all likelihood would have grown further, except Hurricane Frances destroyed all remaining nests with 1.5–2 months left in the nesting/hatching season. Product-limit survival analyses demonstrated substantial differences in turtle nest survival between 2004 versus 2002 and 2003, but not between 2002 and 2003. When analysed as cohorts based on month of nest deposition, no differences were found among 2002, 2003, 2004 for nests deposited in May. These nests received full protection from predation in each of the three years. However, the survival analyses for nests deposited in June, and those deposited in July showed inferior survival for 2004 when predator control was removed for the last half of nesting/hatching.