Zoological Studies

Vol. 49 No. 4, 2010

Interactions between Green Turtles (Chelonia mydas) and Foxes (Vulpes vulpes arabica, V. rueppellii sabaea, and V. cana) on Turtle Nesting Grounds in the Northwestern Indian Ocean: Impacts of the Fox Community on the Behavior of Nesting Sea Turtles at the Ras Al Hadd Turtle Reserve, Oman

Vanda Mariyam Mendonša1,2,*, Salim Al Saady3, Ali Al Kiyumi3, and Karim Erzini1

1Algarve Marine Sciences Centre (CCMAR), University of Algarve, Campus of Gambelas, Faro 8005-139, Portugal
2Expeditions International (EI-EMC International), P.O. Box 802, Sur 411, Oman
3Ministry of Environment and Climate Affairs, P.O. Box 323, Muscat 113, Oman

Vanda Mariyam Mendonša, Salim Al Saady, Ali Al Kiyumi, and Karim Erzini (2010) Green turtles Chelonia mydas nest year round at the Ras Al Hadd Nature Reserve, Oman, with a distinct lower-density nesting season from Oct. to May, and a higher-density nesting season from June to Sept.  On these beaches, the main predators of turtle eggs and hatchlings are foxes Vulpes spp., wolves Canis lupus arabs, and wild cats Felis spp. and Caracal caracal schmitzi.  During 1999-2001, both the nesting behavior of these turtles and the diets of foxes (the main predator on the beaches) were investigated, and we tested whether female turtles were able to avoid/reduce predation pressure on their eggs and hatchlings on the nesting grounds.  Elsewhere in the region and globally, foxes are known to feed on rodents, lizards, birds, and insects, but at Ras Al Hadd, their diet is basically composed of sea turtle eggs and hatchlings (comprising about 95% in volume), with smaller contributions from other marine invertebrates (mostly ghost crabs Ocypode spp. and large gastropods), although they also sporadically ingested birds and lizards.  The ability to adapt to a diet of sea turtle eggs and hatchlings, on these beaches, is certainly a factor behind the success of this carnivore community in the arid lands of the Arabian Peninsula.  Field experiments indicated that nesting sea turtles recognized both natural predators and humans as threats to their offspring, and this was reflected in modifications to their nesting behavior.  In relatively undisturbed areas (by both natural predators and humans), sea turtle nest density was significantly higher, and nests were placed further away from the surf’s edge, in contrast to results from relatively disturbed areas, where turtle nests were closer to the surf’s edge, thus reducing the distance hatchlings had to travel when they emerge and begin their journey to the sea.  Nesting turtles interrupted their nesting cycle if they sensed the presence of people or foxes, returning to the sea without laying a clutch.  However, if they had already initiated oviposition when they sensed the presence of people and/or predators, they continued, although they significantly increased efforts to camouflage their nests.  Other reasons behind nest site abandonment included sand collapsing events (critical during preparation of the egg chamber) and intraspecific competition for nest sites.  These behavioral patterns of sea turtles result from their evolutionary adaptation to nesting on beaches, which surely played a role in their survival, but also highlight the importance of minimizing human disturbance and activities on turtle nesting beaches.

Key words: Chelonia mydas, Ras Al Hadd, Vulpes cana, Vulpes rueppellii sabaea, Vulpes vulpes arabica.

*Correspondence: E-mail:drvandamendonca@mail.seaturtle.org