Monitoring hawksbill turtle nesting sites in some protected areas from the Persian Gulf (original) (raw)
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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.
Identification of Important Sea Turtle Areas (ITAs) for hawksbill turtles in the Arabian Region
Journal of Experimental Marine Biology and Ecology, 2014
We present the first data on hawksbill turtle post-nesting migrations and behaviour in the Arabian region. Tracks from 90 post-nesting turtles (65 in the Gulf and 25 from Oman) revealed that hawksbills in the Arabian region may nest up to 6 times in a season with an average of 3 nests per turtle. Turtles from Qatar, Iran and the UAE generally migrated south and southwest to waters shared by the UAE and Qatar. A smaller number of turtles migrated northward towards Bahrain, Saudi Arabia and one reached Kuwait. Omani turtles migrated south towards Masirah island and to Quwayrah, staying close to the mainland and over the continental shelf. The widespread dispersal of hawksbill foraging grounds across the SW Gulf may limit habitat protection options available to managers, and we suggest these be linked to preservation of shallow water habitats and fishery management. In contrast, the two main foraging areas in Oman were small and could be candidates for protected area consideration. Critical migration bottlenecks were identified at the easternmost point of the Arabian Peninsula as turtles from Daymaniyat Islands migrate southward, and between Qatar and Bahrain. Overall, Gulf turtles spent 68% of the time in foraging ground with home ranges of 40-60 km 2 and small core areas of 6 km 2 . Adult female turtles from Oman were significantly larger than Gulf turtles by~11 cm x ¼ 81:4 CCL ð Þ and spent 83% of their time foraging in smaller home ranges with even smaller core areas (~3 km 2 ), likely due to better habitat quality and food availability. Gulf turtles were among the smallest in the world x ¼ 70:3 CCL ð Þ and spent an average of 20% of time undertaking summer migration loops, a thermoregulatory response to avoid elevated sea surface temperatures, as the Gulf regularly experiences sustained sea surface temperatures N 30°C. Fishery bycatch was determined for two of the 90 turtles. These spatio-temporal findings on habitat use will enable risk assessments for turtles in the face of multiple threats including oil and gas industries, urban and industrial development, fishery pressure, and shipping. They also improve our overall understanding of hawksbill habitat use and behaviour in the Arabian region, and will support sea turtle conservation-related policy decision-making at national and regional levels.
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.
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.
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
PeerJ
Background There is relatively little published information about sea turtle nesting distribution and seasonality in the Saudi Arabian Red Sea. Upcoming large-scale developments occurring along the Saudi Arabian Red Sea coast could negatively affect many sea turtle nesting beaches with potential impacts on the survival of local populations. Methods In 2019, two coastal beaches and three near-shore islands were surveyed for turtle nesting in the central Red Sea. We recorded all emergences, examined beach morphology, and collected sand samples to determine grain size, moisture content and colour. Results Sea turtle nesting was found at all surveyed sites, though emergence counts were often low. The limited occurrence of nesting at several previously undocumented sites suggests that nesting activity may be widespread, but sparsely distributed, in the central Red Sea region. In addition, nesting at novel sites appeared to favour the seaward side of islands, a pattern that was not observ...
Mendonca, V.M., Al-Kiyumi, A.A., Al-Saady, S.M., Grobler, H.J., Erzini, K., Bait Said, A.S., and Al-Rasbiy, A. 2001. Environment of the nesting and feeding grounds for endangered turtle species in Dhofar (Southern Oman). In Claereboudt, M., Goddard, S., Al-Oufi, H., and McIlwain, J. eds. Proc. 1st International Conference on Fisheries, Aquaculture and Environment in the NW Indian Ocean, Sultan Qaboos University, Muscat, Sultanate of Oman, pp. 151-159. ABSTRACT: The coastal line of the Dhofar Region is about 400 km long, with sandy beaches intercalated by rocky shore. Some sandy beaches are several kilometres long, and human disturbance is limited to artisanal fishery activities. On the other hand, the seasonal monsoon makes these waters very rich in biodiversity. Therefore, the region provides good nesting and feeding grounds for sea turtles. From November 1999 to October 2000, field observations were carried out, on an opportunistic schedule. Turtle nesting activities, and threats to turtle eggs and hatchlings by natural predators and human disturbance were registered. At least two turtle species nest on the area: green turtles Chelonia mydas and loggerhead turtles Caretta caretta. Two short but distinct nesting seasons have been identified: one during the Khareef (Monsoon) and another in late winter - early spring. Fresh tracks of both turtle species were observed on both seasons, and in October 2000, both species were observed on a feeding ground of seagrass around Hino Island. The major predators of turtle eggs were feral dogs around the Salalah Port, and foxes Vulpes spp. and ghost crabs Ocypode spp. elsewhere. Seabirds are the major predators of turtle hatchlings all over the region, especially on the islands. Hino Island holds a nesting population of sooty gulls Larus hemprichii, and the Al Hallaniyat Islands hold colonies of masked boobies Sula dactylatra and Socotra cormorants Phalacrocorax nigrogularis. The green turtle is still harvested for meat on Al Hallaniyat Islands.
Nesting of marine turtles on the Egyptian beaches of the Red Sea
Nesting of two species; the hawksbill Eretmochelys imbricate and the green turtle Chelonia mydas on the Egyptian beaches of the Red Sea were studied. The nesting seasons were extended from May to July with a peak in June for the hawksbill and from June to August with a peak in July for the green turtle. Separate nesting grounds for both species with minimum overlap were observed. In total, 38 beaches were surveyed and classified according to the density of nests and tracks. Out of the 38 surveyed beaches, 8 totally offshore beaches were classified as valuable nesting grounds for the hawksbill and 14 beaches for green turtles (inshore and offshore sites). The quantitative estimation of nesting level (i.e. density of nests and tracks) indicated that there are 3 most valuable nesting offshore beaches for the hawksbill and 8 sites for the green turtle (3 inshore and 5 offshore). During 2001-2008, the nesting activities were estimated quantitatively based on the density of true and false...