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.

Predicting nest survival in sea turtles: when and where are eggs most vulnerable to predation?

“…The widespread introduction of exotic mammalian predators on oceanic islands, which provide critical nesting habitat for many sea turtle species, is particularly problematic. In the absence of human intervention, mammalian predators frequently destroy over 80% of the available nests Nellis & Small, 1983;Engeman et al, 2006;Ficetola, 2008). Predation mitigation is therefore a fundamental component of many sea turtle conservation programs, with considerable time and resources devoted to reducing local predator activity or protecting individual nests (Engeman et al, 2002).…”

Cues used by predators to detect freshwater turtle nests may persist late into incubation

“…First, we used a non-parametric product-limit survival analysis (Kaplan and Meir 1958;engeman et al 2006). The survival time equaled the time (days) from oviposition to the first predator interaction.…”

Integrating invasive mammal eradications and biodiversity offsets for fisheries bycatch: conservation opportunities and challenges for seabirds and sea turtles

“…For many fisheries, much of that discarded bycatch is endangered seabirds and sea turtles-species that spend part of their life breeding on islands and coastal beaches. At those breeding sites, seabirds and sea turtles commonly face additional anthropogenic mortality impacts, such as coastal development, direct human take, and impacts from invasive predators (Caut et al in press;Engeman et al 2006;Jones et al in press). Indeed most seabirds and sea turtles that are threatened by fisheries interactions are concurrently threatened by (Cox 2000).…”