seaturtle.org : MTN : ARCHIVES : Sign In

Hawksbill and olive ridley nesting on Masirah Island was first studied, in detail, in the late 1970s as part of a comprehensive sea turtle survey of the Sultanate of Oman (Ross 1981). This three season survey identified the nesting populations, which had not been previously reported. The annual nesting populations were estimated at 92-124 hawksbills (Ross 1981) and 150 olive ridleys (Ross & Barwani 1982). Both species were observed to nest on Masirah’s southern beaches. Hawksbills were found to concentrate their nesting on Omedu beach and olive ridleys on others (Ras abu Rasas and World Jury Beach), however there was overlap, with olive ridleys nesting on the hawksbill beach and vice versa. The nesting of these species on the same beaches is considered rare according to Prichard and Mortimer (1999).

Since this early survey, no further studies have been undertaken to monitor the hawksbill and olive ridley nesting. More recent turtle monitoring on Masirah has been restricted to the loggerhead and green populations (Baldwin 1992; Clark 2003; Ross 1998). In recent years, a team of wildlife rangers have been charged with monitoring the turtle populations but again the focus has been mainly on the large loggerhead population and the green turtle that is hunted for food.

As part of a three year project to assess and evaluate sea turtle populations in Masirah Island as well as establish a sustainable, general management plan for the Island and surrounding areas (Barr Al-Hikman and the Islands in the Masirah Channel), Masirah’s southern beaches were surveyed between January and March 2006. Turtle nesting levels were assessed together with the threats facing both the adult turtles and their nests.

The southern beaches were historically named and divided using geographical divisions based on prominent landmarks (Baldwin 1992; Ross 1981). More recently, permanent marker posts have been placed to subdivide the coast. We used a combination of these two methods to identify nesting beaches and subdivide longer beaches into shorter sections. For our study, nesting beaches were grouped into three main areas: 1) the South West (SW) beaches (20°12.84’N, 58°38.03’E to 20°09.01’N, 58°38.21’E) that correspond to “Omedu” beach (Ross 1981), a beach to its north and “Ras abu Rasas” beach (Ross 1979) to its south; 2) the South East (SE) beaches (20°09.96’N, 58.38.39’E to 20°10.68’N, 58°39.91’E) that incorporate “World Jury Beach” and “World Jury Beach East” (Baldwin 1992); and 3) the Ras Shiban beaches (20°10.86’N, 58°39.98’E to 20°13.21’N, 58°43.38’E) that extend eastwards from the South East beaches after a short section of rocky shore and are divided with permanent beach markers into approximate 2km stretches (Figure 1).

Figure 1. The monitored southern beaches of Masirah Island shown in their regional setting.

None of the beaches exhibit significant development. There are a few, seldom-used, wooden fishermen’s huts near a fish landing area on the South West beaches and a further three fish landing areas on the Ras Shiban beaches. A coastal road, circling the island, used to be a rough dirt track and now has been almost completely paved on the west coast with progress made round the southern tip of the island to the south east beaches. The intention is to pave the entire ring road.

Methods

Day-time beach surveys, to record adult tracks as nests, were carried out on foot or using a 4x4 all terrrain vehicle (ATV) on Masirah’s southern beaches (Figure 1) between January 5 and March 26, 2006. The monitoring period did not cover the entire nesting season for either species. Using data from Ross and Barwani (1982), approximately 85% of the hawksbill and 50% of the olive ridley nesting season was covered.

Adult turtle emergences were classified and nesting or non-nesting depending on the appearance of the track. Egg deposition was not confirmed through uncovering the eggs in each nest as the researchers have much experience at observing and assessing nesting activity where subsequent clutch verification is undertaken. In order to not re-record turtle emergences, each new track was marked by scraping a line through it, near the top, and was driven over, above the high tide line, by the ATV. Opportunistic nocturnal surveys were undertaken for limited hours, mainly in March, to identify nesting turtle species so that individual tracks could be firmly assigned to a specific species. Beach surveys were usually made at 1 to 3 day intervals, but on two occasions the beaches were not monitored for up to 7 days.

Results and Discussion

Although hawksbill and olive ridley nesting is evidently concentrated on the southern beaches, sporadic nesting by hawksbills on other beaches, as noted by Ross (1981), was again documented through photographic identification of individuals that nested near Ras Hilf at the extreme north of the Island.

Fifteen turtles were observed during the nocturnal surveys on Omedu and the SE beaches. One turtle of each species was seen on the SE beaches and six olive ridleys and seven hawksbills were seen on Omedu beach. This confirmed that both species of turtle were still nesting on Masirah. However, as so few turtles were observed and the tracks could not be assigned to a specific species, no estimate for the proportion of nests contributed by either species can be made and hence all nesting activity was pooled for analysis.

Table 1. Spatial distribution of sea turtle nesting activity on Masirah’s southern beaches, 2006.

A total of 462 nests from 752 emergences (61.4% nesting success) were recorded on the monitored beaches (Table 1), however, nesting activity was not evenly distributed in time or space. Nesting levels were low in January and increased through February and March (Figure 2) as found by Ross and Barwani (1982). Nesting activity on the SW beaches was concentrated on Omedu beach with 66 nests/km, the SE beaches were the most densely nested area with 94 nests/km and nest density dropped from west to east along the Ras Shiban beach which ranged from 35 to 7 nests/km (Table 1). There was no obvious reason for the distribution of nests. The long Ras Shiban beach is quite uniform along its length providing no indication why the western side was preferred, but from limited observations, hawksbills seemed to prefer beaches with off-shore rock or coral reef.

Figure 2. Temporal Distribution of sea turtle nesting activity on Masirah’s southern beaches, 2006.

On Masirah, olive ridleys and hawksbills have been observed to make a maximum of 3 nests/season (Ross 1979, 1981). Using this number of nests per individual we calculate there were at least 154 turtles nesting in 2006. Hawksbills have an average internesting interval of 14.5 days (Miller 1997) and olive ridleys on Masirah were found to have a 21 day internesting interval (Ross 1979) and hence the total number of nests made in 14 days should provide a conservative maximum estimate for population size. By this method it is estimated there were over 250 turtles nesting in 2006. The estimated nesting population size for 2006 is therefore 150-250 turtles.

The combined hawksbill and olive ridley yearly nesting population had been roughly estimated to range from 240-275 turtles (Ross & Banwari 1982) and our results place the population still in the lower part of this range. Caution must be used when comparing our results with previous studies, particularly because we were unable to distinguish species and an increase in one population may mask a decrease in the other.

During the survey period, seven attempts at poaching turtle nests were recorded, equating to 1.5% of the nests laid. Additionally, one nesting turtle was poached from the beach, based on observing an “up track” ending in a pit and whence a large drag mark with a set of footprints on either side lead to vehicle tracks at the top of the beach. The other main anthropogenic threats observed were dumping or drying of fishing nets on the beaches and vehicles traversing the beach at fish-landing sites. None of these problems were extensive, affecting only a small proportion of the nests and turtles. However, poaching should be deterred, the beaches should be cleaned of problematic rubbish, vehicle traffic should be minimised on the beach year-round as loggerheads and green turtles use these beaches to nest in other seasons (Clarke 2003) and fishermen should be encouraged to dry their nets away from the nesting habitat to ensure maximum survival chances for the turtle populations.

Natural potential, threats to nests and hatchlings that were observed included the presence of numerous ghost crabs (Ocypode spp.) on the nesting beaches and the possibility of nest flooding or destruction by high tides and beach erosion with nest flooding most likely to be the worst threat. However, no incidences of ghost crab predation on hatchlings, or nests exposed due to beach erosion were observed during the study period.

Conclusions

This study indicates that hawksbill and olive ridley nesting still occurs in low but significant numbers on Masirah Island. However, more focused studies on certain beaches, to repeat the early population assessments, should be undertaken to make better estimates of the proportion of nests that can be attributed to either species. Specifically, in February, March (and possibly April) Omedu beach of the South West group should be closely monitored as it is believed to host the majority of hawksbill nesting on the Island and the 2km of the SE beaches should be monitored for the majority of the olive ridley nesting from February to April. In this way approximately 55% of the nesting activity would be recorded through monitoring only 3km (23%) of the nesting habitat.

The southern beaches are currently undeveloped and suffer none of problems caused by construction for habitation, tourism or industry. They should be kept this way to protect the turtle populations. However, improved access to the southern beaches afforded by the ongoing road upgrading may bring pressure on the local community to create facilities for visitors to the area and encourage development. If development must occur it should be undertaken in a “turtle friendly” manner that does not adversely affect the nesting populations.

Acknowledgements: We wish to thank Mr Khamis, Municipal Director of Masirah, for supporting this project, providing the 4x4 ATV to facilitate beach surveys and the assistance of the wildlife rangers. Maps for Figure 1 were created using MapTool <https://seaturtle.org/maptool> a free-of-charge GIS utility of SEATURTLE.ORG. The project was funded by the TOTAL Foundation and was carried out, under contract, by IPEDEX LLC. We also wish to thank two reviewers whose comments significantly improved the original manuscript.

CLARK, D. 2003. Beach characteristics and turtle nesting behaviour on Masirah Island, Sultanate of Oman. Unpublished MSc dissertation. University of St Andrews, UK. 54pp.

BALDWIN, R.M. 1992. Nesting Turtles on Masirah Island. Unpublished report. Ministry of Regional Municipalities and Environment, Oman. 17pp.

MILLER, J.D. 1997. Reproduction in sea turtles. In: P.L. Lutz and J.A. Musick (Eds.). The Biology of Sea Turtles. CRC Press. Boca Raton, Florida. USA. pp. 51-81.

PRITCHARD, P.C.H. & J.A. MORTIMER. 1999. Taxonomy, external morphology, and species identification. In: K.L. Eckert, K.A. Bjorndal, F.A. Abreu-Grobois and M. Donnelly (Eds.). Research and Management Techniques for the Conservation of Sea Turtles. IUCN/SSC Marine Turtle Specialist Group Publication No. 4. pp. 21-38.

ROSS, J.P. 1979. Sea Turtles in the Sultanate of Oman. Unpublished report. IUCN/WWF Project 1320. 53pp.

ROSS, J.P. 1981. Hawksbill turtle Eretmochelys imbricata in the Sultanate of Oman. Biological Conservation 19: 99-106.

ROSS, J.P & M.A. BANWARI. 1982. Review of sea turtles in the Arabian area. In: K.A. Bjorndal (Ed.). Biology and Conservation of Sea Turtles. Smithsonian Institute Press, Washington D.C. pp. 373-383.

ROSS, J.P. 1998. Estimations of the nesting population size of loggerhead sea turtles, Caretta caretta, Masirah Island, Sultanate of Oman. In: S.P. Epperly and J. Braun (Comps.). Proceedings of the 17th Annual Symposium on Sea Turtle Biology and Conservation. NOAA Technical Memo. NMFS-SEFSC-415. pp. 84-87.