Study

Comparisons of Lethal and Nonlethal Techniques to Reduce Raccoon Depredation of Sea Turtle Nests

  • Published source details Ratnaswamy M.J., Warren R.J., Kramer M.T. & Adam M.D. (1997) Comparisons of Lethal and Nonlethal Techniques to Reduce Raccoon Depredation of Sea Turtle Nests. The Journal of Wildlife Management, 61, 368-376.

Actions

This study is summarised as evidence for the following.

Action Category

Remove or control predators using lethal controls: Sea turtles

Action Link
Reptile Conservation

Protect nests and nesting sites from predation using artificial nest covers: Sea turtles

Action Link
Reptile Conservation

Protect nests and nesting sites from predation using conditioned taste aversion

Action Link
Reptile Conservation
  1. Remove or control predators using lethal controls: Sea turtles

    A replicated, randomized, controlled study in 1993–1994 on a long sandy beach in Florida, USA (Ratnaswamy et al. 1997) found that raccoon Procyon lotor control on sections of beach did not reduce predation of loggerhead turtle Caretta caretta nests compared to sections with no control. Predation of turtle nests was similar in sections of the beach with raccoon control (1993: 489 of 1,359 nests, 36% predation; 1994: 460 of 1,686, 27%) and those with no control (1993: 72 of 231 nests, 31%; 1994: 92 of 379, 24%). In 1993–1994, a long stretch of barrier beach (37 km) was broken down into four experimental blocks, and around half of each block (4 km) was selected for raccoon removal. Raccoons were captured with live traps baited with sardines, anesthetised and lethally injected (215 individuals; estimated as 50% of raccoon population). Nests in the remainder of the block were either received no treatment or were part of further tests of the effect of nest screening and taste aversion on predation. Nests were monitored 2–4 times/month in 1993 and 2–3 times/week in 1994.

    (Summarised by: Maggie Watson, William Morgan)

  2. Protect nests and nesting sites from predation using artificial nest covers: Sea turtles

    A replicated, randomized, controlled study in 1993–1994 on a long sandy beach in Florida, USA (Ratnaswamy et al. 1997) found that covering sea turtle nests with a wire screen resulted in lower nest predation compared to when no screen was used. Predation of screened nests (9% and 7% of 499 and 737 nests predated) was lower than for nests with no screen (31% and 24% of 231 and 379 nests predated). An additional group of nests that received both a screen and a conditioned taste aversion treatment had similar predation to both screened nests and non-screened nests (16% and 12% of 531 and 720 nests predated). In 1993–1994, a long stretch of barrier beach (37 km) was broken down into four experimental blocks, and around 2.5 km of each block was selected for a screening trial, with two-thirds of nests in the area receiving a screen (1.2 x 1.2 m wire screen, with 5.1 x 10.2 cm mesh). Screens were secured with steel rebar at each corner. Nests in the remainder of the block either received no treatment or were part of further tests of the effect of conditioned taste aversion or raccoon Procyon lotor removal. Two-thirds of nests in the taste aversion area were also screened. Taste aversion involved provision of chicken eggs injected with 10 mg of oral oestrogen. Turtle nests were monitored 2–4 times/month in 1993 and 2–3 times/week in 1994.

    (Summarised by: Maggie Watson, William Morgan)

  3. Protect nests and nesting sites from predation using conditioned taste aversion

    A replicated, randomized, controlled, before-and-after study in 1993–1994 on a long sandy beach in Florida, USA (Ratnaswamy et al. 1997) found that conditioned taste aversion using artificial nests with unpalatable eggs did not reduce predation of loggerhead turtle Caretta caretta nests compared to areas where no taste aversion was attempted. The number of nests predated in areas with taste aversion were similar (46% and 36 % of 246 and 390 nests) to the number of nests predated with no treatment (31% and 24% of 231 and 379 nests). Additional nests in the taste aversion area that were also covered with a wire screen were predated less than nests receiving just taste aversion (16% and 12% of 531 and 720 nests), but a similar amount to nests receiving no treatment. Consumption of artificial nests were statistically similar before (42–70% of eggs eaten), during (50–60%) and after (67–70%) taste aversion treatment. In 1993–1994, a long stretch of barrier beach (37 km) was broken down into four experimental blocks, and around 2.5 km of each selected for conditioned taste aversion. Nests in the remainder of the block either received no treatment or were part of further tests of the effect of nest screening or raccoon Procyon lotor removal. Fifteen artificial nests were placed in each taste aversion area consisting of 10–15 chicken eggs placed on the sand surface. Egg consumption was monitored during a pre-treatment phase (8 nights, untreated eggs), a treatment phase (8–9 night, eggs injected with 10 mg oral oestrogen) and a post-treatment phase (5 nights, untreated eggs), with eggs replaced daily. Turtle nests were monitored 2–4 times/month in 1993 and 2–3 times/week in 1994.

    (Summarised by: Maggie Watson, William Morgan)

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