seaturtle.org : MTN : ARCHIVES : Sign In
Figure 1. Cerdocyon thous footprints and one individual found as road-kill near the study area.
One of the different management actions to reduce nest predation that was considered is predator removal (Barthon & Roth 2006; Meier & Varnham 2004; O’Toole 2003; Ratnaswamy & Warren 1998; Woolard et al. 2004; Yerli et al. 1997; Zeppellini et al. 2007). However, given the possible cascade effects of removal or eradication programs, as well as ethical and legal implications, this option was not pursued. As an alternative, we investigated the use of flags over the nests as a possible deterrent to foxes. We used flags made from 1.20 m wooden sticks with 50 x 80 cm resistant textile. On some flags, we also attached a metal rattle, to check if adding sound to the flags would increase their predator avoidance effectiveness (Fig. 2).
Figure 2. Flags used to reduce nest predation by wild dogs in northeastern Brazil. Upper flag does not contain rattles in contrast of the lower, in which the small circle indicates the rattles in detail.
Following an analysis of predation rates in different areas of Mangue Seco, we selected an extension of 19 km of beach to analyze nest predation events and to test the effectiveness of the flags to reduce predation rates. During the 2007/2008 nesting season, from September to March, the beach was patrolled daily and all nests were registered. The study area contains permanent post markers placed at 1 km intervals along the beach and were used to record nest site positions and to guide the flag use.
Three different treatments were used to protect the nests: grid (G), grid and flag (GF), grid and flag with rattle (GFR), and applied independently to nests laid between the kilometers, following this sequence described above. This standardized placement strategy helped avoid concentrating a particular treatment in particular areas of the study beach. Nests protected only with grids were considered as control nests in the study.
A total of 635 nests were recorded in the study area: 388 olive ridley nests, 97 loggerhead nests, 3 hawksbill nests, and 147 nonidentified nests. Fox predation was observed in 145 nests (22.8%), of which 66 (45.5%) were olive ridley nests, 65 (44.8%) were non-identified nests, 13 (9.0%) were loggerhead nests and 1 hawksbill nest. Predation rates indicate no clear preference for nests of a particular sea turtle species, which is consistent with the opportunistic foraging behavior of crab-eating foxes (Berta 1982, Michalski et al. 2006).
Eighty-eight nests were predated before monitors could set protection of any kind, comprising 62.1% of all instances of nests with animal predation. Two nests were harvested for human consumption before protection, and were excluded from animal predation analyses (Table 1). Furthermore, of the 545 nests that received some kind of protection, 57 (10.5%) were predated, of which 44 (77.2%) were protected with only a grid (Table 1).
Table 1. Nest protection strategies and numbers of nests predated and successfully hatched. Nests initially marked and subsequently lost (through tidal erosion, human predation, or other reasons) are grouped in the Other column.
A significant difference was observed between the rate of predation of nests protected with grids alone vs. nests with grids and flags (Χ2 = 25.98, d.f. = 1, p < 0.001), and also between nests protected by grid alone vs. those protected with grids and flags with a rattle (Χ2 = 17.65, d.f. = 1, p < 0.001). This indicates the flag protection effectiveness as a good method to reduce nest predation when compared to the grid itself. However there was no significant difference in rate of predation between nests protected by flags with or without a rattle (Χ2 = 0.11, d.f. = 1, p > 0.05). Thus, it appears that the rattle did not increase the efficiency of the flags to deter predation. Overall, 324 nests were protected with grids and flags (with or without rattle), and the rate of predation of this group was 4.0%, which was significantly lower than 24% predation rate for nests protected by grids alone (Χ2 = 37.52, d.f. = 1, p < 0.001).
We suggest that flags are a simple and low cost solution to reduce sea turtle nest predation by foxes in northern Bahia. It may be the case that constant coastal winds, typical of northern Bahia, may contribute to the effectiveness of the flags, and flags may be less a less effective deterrent in other areas. There is also the possibility that over time, foxes may habituate to the flags and even begin to associate flags with a food source, as has been observed in the Mediterranean (Yerli et al. 1997). However, Tubberville & Burke (1994) tested whether flag markers attracted mammalian predators of fresh water turtle nests, and found that predators did not develop an association between flags and food availability. Tubberville & Burke (1994) also recommended alternating between different kinds of markers, to reduce the likelihood that mammalian predators may associate certain markers with turtle nests. Overall, we recommend that long term research is needed to properly address these issues.
Previously suggested methods for reducing mammalian predation of sea turtle nests include predator removal, either by trapping, using poisons or chemical repellents, and relocation of nests out of reach of predators. There are ethical and ecological implications associated with these strategies (Barthon & Roth 2006; Bouchard & Bjorndal 2000; O’Toole 2003; Ratnaswamy & Warren 1998), not to mention legal hurdles: the crab eating fox is a is a natural predator in northern Bahia, not an exotic or introduced predator; this would make it difficult to get legal permission to remove it from coastal habitats.
In terms of ecological implications of predator removal from our study area, the crab eating fox is a generalist and opportunistic hunter, preying specially on small mammals, birds, invertebrates and fruits (Berta 1982). Its removal may have various impacts on the local environment, including reduction of seed dispersion, changes in nutrient flux and also impacts on the abundance of other sea turtle predators, such as crabs (Ratnaswamy & Warren 1998). Also, information is lacking on the abundance trends of this fox and its population dynamics with our study area, thus complicating the design of an effective removal strategy that would not extirpate the local population.
In terms of using nest relocation to reduce predation rates, while the use of hatcheries is accepted as a positive conservation strategy in some cases, and can be an important tool for environmental education (Marcovaldi & Marcovaldi 1999), they can alter hatchling sex ratios, decrease nest hatch success, and reduce the transport of nutrients from natural sea turtle nests into sandy dune environments (Morreale et al. 1982, Bouchard & Bjorndal 2000). Our results suggests that placing flags next to sea turtle nests helps reduce nest predation and obviates the need to use more drastic predator control measures. Indeed, using flags is simple and relatively economical. We plan to investigate in the near future whether it is necessary to use grids for sea turtle nest protection, or if flags are sufficient to keep foxes from damaging nests.
Acknowledgments: We thank the Projeto Tamar field team at Sítio do Conde station, especially: Pêta, Pépe, Raimundo, Carlinhos and Beca for daily surveys efforts and making the flags. Matthew H. Godfrey, Paulo Simões-Lopes, Juçara Wanderlinde and Tânia Castellani helped read earlier drafts. The idea to use flags to deter nest predators came from Pêta, one of Projeto Tamar’s employees from the local community, and to whom we are grateful. Projeto TAMAR, a conservation program of the Brazilian Ministry of the Environment, is affiliated with ICMBio, is co-managed by Fundação Pró-TAMAR and officially sponsored by Petrobras.
BARTON, B. T. & J.D. ROTH, 2006. Racoon removal on sea turtles nesting beaches. Journal of Wildlife Management. 714: 1234-1237.
BERTA A. 1982. Cerdocyon thous. Mammalian Species 186: 1-4.
BOUCHARD, S.S. & K.A. BJORNDAL, 2000. Sea turtles as biological transporters of nutrients and Energy from marine to terrestrial ecosystems. Ecology 81: 2305-2313.
ARCOVALDI, M.Â. & A. LAURENT. 1996. A six season study of marine turtle nesting at Praia do Forte, Bahia, Brazil, with implications for conservation and management. Chelonian Conservation & Biology 2: 55-59.
MARCOVALDI, M. Â. & G.G. MARCOVALDI, 1999. Marine turtles of Brazil: the history and structure of Projeto TAMAR-IBAMA. Biological Conservation 91: 35-41.
MEIER, G.G. & K. VARNHAM, 2004. Rat eradication as part of a green turtle (Chelonia mydas) conservation programme in Indonesia. Marine Turtle Newsletter 106:1-12.
MICHALSKI, F., P.G. CRAWSHAW, T.G. DE OLIVEIRA & M.E. FABIAN. 2006. Notes on home range and habitat use of three small carnivore species in a disturbed vegetation mosaic of southeastern Brazil. Mammalia 70: 52–57.
MORREALE, S.J., G.J. RUIZ, J.R. SPOTILA AND E.A. STANDORA.1982. Temperature dependent sex determination: current practices threaten conservation of sea turtles. Science 216:1245 1247.
O´TOOLE , T. 2003. Protecting sea turtle nests from raccoon depredation at Sebastian Inlet State Park. In: Pilcher, N.J. (Comp.). Proceedings of the 23rd Annual Symposium on Sea Turtle Biology & Conservation, NOAA Tech. Memo. NMFS-SEFSC-536, pp. 88-89.
RATNASWAMY, M.J. & R.J. WARREN. 1998. Removing raccoons to protect sea turtle nests: are there implications for ecosystem management? Wildlife Society Bulletin 26: 846-850.
TUBERVILLE, T.D. & V.J. BURKE. 1994. Do flag markers attract turtle nest predators? Journal of Herpetology 28: 514-516.
WOOLARD, J., R.M. EENGEMAN, H.T. SMITH & J. GRINER. 2004. Cheloniidae (Marine turtle) nest predation. Herpetological Review 35: 379-380.
YERLI, S., A.F. CANBOLAT, L.J. BROWN & D.W. MACDONALD. 1997. Mesh grids protect loggerhead turtle (Caretta caretta) nests from red fox (Vulpes vulpes) predation. Biological Conservation 82: 109-111.
ZEPPELINI, D., R. MASCARENHAS & G.G. MEIER. 2007. Rat eradication as part of a hawksbill turtle (Eretmochelys imbricata) conservation program in an urban area in Cabedelo, Paraíba State, Brazil. Marine Turtle Newsletter 117:5-7.