Identification of Important Sea Turtle Areas (ITAs) for hawksbill turtles in the Arabian Region (original) (raw)
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Marine Biology
Adult sea turtles migrate between foraging areas and nesting sites that may be 100 s–1000 s of km away. Little is known of the connectivity between these sites in the Arabian region for green sea turtles. We document linkages between two foraging areas in the United Arab Emirates (UAE) with key nesting sites and provide insights on effectiveness of marine protected areas for green sea turtles. Tracking 45 adult green sea turtles Chelonia mydas from foraging areas in the UAE, we show that the primary nesting destination for turtles foraging in Bu Tinah in the UAE is Ras al Hadd in Oman. The turtles use the waters of the UAE, Iran and Oman during breeding migrations and generally stay ~ 20 km off the coast, in waters 10–20 m deep except when crossing the Sea of Oman. Turtles display substantial fidelity to the original foraging sites, often traversing other known foraging sites when returning from the breeding migration. A small proportion of turtles also utilise more than one foragin...
Monitoring hawksbill turtle nesting sites in some protected areas from the Persian Gulf
Acta Oceanologica Sinica, 2019
Iranian nesting populations of the critically endangered hawksbill turtle (Eretmochelys imbricate) are some of the most important in the Indian Ocean. In this study, four of the most important hawksbill nesting grounds in the Persian Gulf, situated within three Iranian marine protected areas, were surveyed during nesting season, including Nakhiloo, Ommolgorm and Kharko Islands and the mainland beaches of the Naiband Marine-Coastal National Park (NMCNP). We present GIS maps of these key nesting grounds and describe sand texture of key nesting zones, along with conservation recommendations. About 9.2 (28.3%) out of 32.5 km of all shores surveyed in this study were used by nesting hawksbill turtles follows: Nakhiloo: 1.4 km (52% of potential nesting area); Ommolgorm: 1.94 km (40%); Kharko: 3.4 km (28%), and NMCNP: 2.46 km (18.9%). The average nesting density was calculated as 131 nests/km at Nakhiloo, 76 nests/km at Ommolgorm, 7 nests/km at Kharko, and 15 nests per km at NMCNP. Highest nesting density was observed in Nakhiloo and Ommolgorm. It is thought that high hawksbill nesting density in these islands seems likely a result of limiting adequate nesting shores rather than the size of population, and also low density in Kharko and NMCNP more related to past and current pressures and low population density. With the exception of Ommolgorm Island, sands at the nesting grounds were well sorted. Grain size indicated that female hawksbill turtles in the Iranian Persian Gulf nest in sands that are generally mixed, with mean grain size ranging from coarse sands (0.4Φ; ~0.5-1 mm) to fine sands (2Φ; ~0.25 mm). We provide and discuss conservation recommendations and suggestions for future.
The hawksbill turtle nesting population of the Dimaniyat Islands, in the Gulf of Oman
Al Kiyumi AA, Mendonca VM, Grobler HJ, Al Saady SM, Erzini KA. 2002. The hawksbill turtle nesting population of the Dimaniyat Islands, in the Gulf of Oman. Proc 20th Int Symp Sea Turtle Biol Conserv, Florida, USA, 2000. NOAA Tech Memo NMFS-SEFSC 447:243-244 EXTENDED ABSTRACT: Hawksbill turtles Eretmochelys imbricata are considered critically endangered species (Groombridge, 1982; Groombridge and Luxemore, 1989; Meylan and Donnelly, 1999). Therefore, knowledge concerning the status and ecology of the remaining populations is of vital importance for their conservation. Coral reef areas like the Dimaniyat Islands, in the Gulf of Oman, still provide good feeding and nesting grounds for this species. This uninhabited archipelago of nine sparsely vegetated islands is also free from mammal predators and it is not easily reached even by the most adventurous tourists, even though it is located less than 100 km north of Muscat. Prior to our study, the only available extensive information on this specific population was recorded in 1986 by Salm (1991), who also referred to this population in later publications (Salm and Salm, 1991; Salm et al., 1993), where he has made clear that due to the protected status of these islands and the high pollution levels that exist in the Arabian Gulf, this is the last sanctuary of any real value to hawksbills in the region. In spring and early summer 1999, during the nesting season of the hawksbill turtles, we decided to return to the Dimaniyat Islands in order to up-date our information on this population. In our study, we observed the number of tracks per night during our field trips to the islands, from April to July. We also tagged female turtles coming ashore to nest, and recorded data on curved carapace length and width. At the end of the nesting season of hawksbill turtles, in late June and early July, we counted the number of nests on all beaches of each island, by walking in pairs parallel to the water line and shouting to each other the nest number. The area of the beaches was also recorded in order to obtain nesting densities. Beach selectivity was tested comparing nest densities, using one-way Analysis of Variance, ANOVA (Underwood, 1997). As previously recorded, we also observed that the peak of the nesting season was in April. A maximum of 16 tracks per night was recorded; two more than the previous maximum found by Salm in 1986 (Salm, 1991). Mean size of hawksbill turtles was larger in 1999 (mean ± 95% confidence intervals = 81.81 ± 1.28 cm; range = 79 - 84 cm; n = 5 individuals) than it was found in 1986 (mean = 76 cm; n = 9 individuals, Salm, 1991). It is expected to continue our study in order to increase our sample size, and to observe any trends. However the new size records of female hawksbill turtles are now closer to those found further south in the Indian Ocean in the Seychelles (e.g. Brook and Garnett, 1983; Diamond, 1976), and in the Great Barrier Reef in Australia (Limpus, 1980, 1992). Against our expectations, the total number of nests in 1999 (1205 nests), showed an increase of 33%, when compared with data from 1986 (900 nests; Salm, 1991). In fact, with the exception of Haywt island, the number of nests have increased on all islands. However natural fluctuations in this population are not known. It may also be that the nesting population is increasing, or that female turtles are shifting from their nesting grounds in the nearby mainland beaches, just 20 km away, to these less disturbed islands, even thought there is some fishing activity in the coral reef areas, especially at Jabal Al Kabier, the largest island and at Al Kharabah, the most eastern island. Nevertheless, no significant differences were found between the islands when comparing nests/beach (ANOVA: F = 0.8, P = 0.56) or nests/area (m2) (ANOVA: F = 1.08, P = 0.39), which suggests that there is no beach preference by these nesting females on these islands. We also consider our counts as underestimates as some nests were on top of previous ones (nest density ranged from 0.2 to 1.4 nests/m2), showing that space might be a very limiting factor, if not the main limiting factor, for the expansion of the population of hawksbills in the Dimaniyat Islands, as we recorded 1205 nests on 1.5 km of beach on the six islands where nesting activity was observed, which is equivalent to 0.8 nests/m of beach or 800 nests/km of beach in a nesting season.
Oryx, 2007
In marine turtles the selection of oviposition habitat is a key determinant of offspring success. I investigated which environmental features influenced the nesting activity and nest distribution of the hawksbill turtle Eretmochelys imbricata by daily monitoring of a rookery on the coast of the Arabian Gulf, in Qatar. I mapped the distribution of turtle nests and unsuccessful nesting attempts and measured key beach features. Data were analysed using autoregressive models, a specific regression technique dealing with spatial autocorrelation. Distribution of nests and unsuccessful nesting attempts were strongly spatially autocorrelated. In some areas almost all the turtles that approached the beach excavated a nest, whereas in other areas nesting was scarce but many unsuccessful attempts were observed. Turtle activity was lower in areas with a steep coastline and high rock cover. Nest density was higher on beaches with a low slope and little rock cover, and with soft soil and high vegetation cover. The density of unsuccessful nesting attempts was higher in areas with hard soil and low vegetation cover. These results are relevant for the management and restoration of nesting areas for this Critically Endangered species.
Mendonca, V.M., Al-Kiyumi, A.A., Al-Saady, S.M., Grobler, H.J., and Erzini, K.. 2001. Environment on the densest known nesting grounds of the critically endangered Hawksbill turtle Eretmochelys imbricata on the Dimaniyat Islands, Gulf of Oman. In Claereboudt, M., Goddard, S., Al-Oufi, H., and McIlwain, J. eds. Proc. International Conference on Fisheries, Aquaculture and Environment in the NW Indian Ocean, Sultan Qaboos University, Muscat, Sultanate of Oman, pp. 160-168. ABSTRACT: The Dimaniyat Islands in the Gulf of Oman, an archipelago of nine uninhabited islands surrounded by coral reefs, provide good feeding and nesting grounds for hawksbill turtles Eretmochelys imbricata. During the nesting seasons of 1999 and 2000, extensive surveys of the Dimaniyat Islands permitted a better understanding of this turtle population, and of threats imposed by natural predators and human disturbance. For this species, the Dimaniyat Islands population is the densest known on earth, with at least 250 annual nesting females nesting on 1.5 km of beach front. The nesting season extends from February-March to July-August with a peak around April-May. Ghost crabs Ocypode spp. are known to be turtle egg and hatchling predators, but here they did not significantly affect hatching success or survival. There are no mammal predators on the islands. Several bird species, including sooty gulls Ichthyaetus hemprichii (formerly Larus hemprichii) and birds of prey such as osprey Pandion haliaetus and sooty falcons Falco concolor nest on the islands, during turtle hatchling season. Nevertheless, the effect of bird predation on turtle hatchlings can only be significant if hatching takes place in daylight hours or during full-moon nights. Predation by aquatic predators, especially by reef sharks Carcharhimus melanopterus and other larger fish species might be significant. Human presence is minimal, but fishing nets left on the beach to dry and repair are a threat for hatchlings, as they may become entangled and either die by desiccation or become more exposed to birds. Keywords: sea turtle, reproduction, ecology, Oman, conservation
Short-term behavioural responses to thermal stress by hawksbill turtles in the Arabian region
Journal of Experimental Marine Biology and Ecology, 2014
We present a previously unrecorded short-term behavioural response by hawksbill sea turtles to elevated sea surface temperatures in the Persian/Arabian Gulf. Surface waters typically exceed 30°C for sustained periods during the summer, and can be likened to a natural living laboratory for understanding thermoregulatory behaviour by marine species in the face of climate change and elevated global temperatures. We satellite-tracked 90 post-nesting hawksbill turtles between 2010 and 2013 as part of a larger programme to elucidate turtle foraging habitats and post-nesting behaviour. We used 66 of these datasets, where turtles clearly departed and returned to foraging grounds, for these analyses. Sea surface temperatures during the summer averaged 33.5°C and peaked at 34.9°C. During these elongated periods of elevated temperatures (June-August) the turtles temporarily migrated an average of 70 km to deeper and cooler waters at northern latitudes, returning after 2-3 months (September-October) back to original feeding grounds. Temperature differential T Δ between foraging and summer loop habitats was significantly different and approximated −2°C. Turtles undertaking summer migration loops generally moved in a north-easterly direction toward deeper water, returning in a south-westerly direction to the shallower foraging grounds. Swim speeds were significantly higher and orientation was less omnidirectional during the migrations than when foraging. The outbound migrations were significantly inversely correlated with temperature, but were not linked to chlorophyll-a, geostrophic currents or sea surface height. The turtles' preference for returning to the same foraging grounds suggests a lack of other substantial influences which might have precipitated the temporary summer migration loops. Our results indicate that Gulf hawksbills employ thermoregulatory responses which take them out of high temperature and potentially physiology-threatening conditions. These findings improve our overall understanding of hawksbill habitat use and behaviour in a climate-challenged environment, and support sea turtle conservation-related policy decision-making at national and regional levels.
Nesting ecology of hawksbill turtles, Eretmochelys imbricata, in an extreme environmental setting
PLOS ONE
Relatively few details of hawksbill turtle (Eretmochelys imbricata) nesting ecology exist within the Arabian Gulf. Moreover, little is known about how their nesting dynamics compare to nesting populations throughout the rest of the world. Due to the extreme environmental setting, nesting ecology of hawksbills in the Arabian Gulf is of significant interest to researchers and conservationists. The current research reports on a long-term tagging and monitoring program undertaken at Fuwairit beach, Qatar. To investigate nesting behavior, site surveys and tagging were employed from 2010 to 2016. Presence of nests and clutch sizes were confirmed by excavation. Over the entire study period, nesting hawksbills had a mean curved carapace length of 70.8 cm (SD±2.8). A total 187 nests were confirmed, which contained a mean 78.9 eggs per clutch (SD±17.1), over an annual nesting season that lasted an average of 52.2 days (SD±6.3) from the start of April to the start of June. Meta-analysis with other global regions showed these characteristics to be significantly reduced when compared to nesting hawksbills from other populations. Meteorological data analysis showed air temperatures in the Arabian Gulf to increase on average 13.2˚C (SD±0.26) from start to the end of nesting annually, which is significantly greater than other global nesting regions. Their smaller body size and reduced fecundity coupled with the extreme change in ambient air temperatures support the hypothesis that hawksbills in the region are more at risk than the already critically endangered hawksbill populations elsewhere in the world.