Bulletin 42 - November 1990: The Natural History of Merawah Island



The Natural History of Merawah Island

Edited by Peter Hellyer

Table of Contents

Introduction
Members of the team
The Island of Merawah
History and Archaeology
Mammals
Insects
Reptiles
Flora
The Beach and Shells
Birds
Geology
Conclusion



Introduction

On the weekend of May 31 and June 1 1990, at the invitation of His Excellency Major General Sheikh Mohammed bin Zayed al Nahyan, the Emirates Natural History Group sent a team of five persons to the island of Merawah, north west of the town of Mirfa in the Emirate of Abu Dhabi, to carry out a brief interim survey of the Natural History of the island, with particular reference to its bird life, but also with attention being paid to its flora and other fauna.

The team was on the island from the early morning of May 31 until after lunch on June 1 and was provided with accommodation and transport both to and from Mirfa, and on the island itself, courtesy of Sheikh Mohammed bin Zayed.

The report that follows is a summary of the main findings of the survey. Further visits to the island at the time of the main autumn or spring bird migrations, and after winter rainfall to study the flowering plants, would add substantially to the information that can be obtained, while more information can also be obtained from trapping of insects, mammals and reptiles, and from detailed discussions with fishermen resident on the island.

This Interim Report also makes some tentative recommendations related to conservation and management of the island's natural environment.

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Members of the team

The main participants in the two-day survey were as follows:

J.N.B. (Bish) Brown
Peter Hellyer
Martin Pitt
Elizabeth Pitt
David Robinson

Assistance in the collection of some specimens was also provided by Hisham Hellyer.

Additional information was provided by Rob Western (flora), Maarten Verhage (location), Terry Adams (geology), and the Abu Dhabi Company for Onshore Operations (details of a 1984 ecological survey).

This Survey Report was compiled and edited by Peter Hellyer with individual contributions by Terry Adams, Bish Brown, Martin Pitt and Elizabeth Pitt (see sections).

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The Island of Merawah

Location

The island of Merawah lies in the Arabian Gulf, within the waters of the Emirate of Abu Dhabi, to the north of the Khor al Bazm. To the west is the small island of Al Fiyah, to the southeast the island of Junaina, and to the east the island of Abu al Abyad. It is around 15 km north of the main coastline and about eight km north west of Junaina.

Al Fiyah and Merawah, together with the small island of Hail, several kilometers to the northeast, and a number of small sandbanks, are situated on a large sand bank, and at low tides extensive areas of sand are exposed, except for the southeastern corner. A rocky outcrop at the southwestern corner, on the highest point of the island, at around seven meters, is the site of Trig Point 23T.



General Description

There is one natural source of fresh water, near the southwestern end of the low rocky sandstone ridge running across the center of the island, and near the village of Ghurbah. We were informed (by Mohammed al Bawardi) that a layer of rock beneath the surface traps the run off of rainwater from that part of the southern side of the ridge, and a number of small wells have been dug for the use of local inhabitants, surrounded by a low dam or bund. The wells are still in use and the water level at the time of the survey was a little more than a meter below the surrounding natural land surface. The surrounding area, including the run off area, contains a dense biomass of natural vegetation but apparently no species that are not salt tolerant.

The remainder of the island is low lying sand, with an extensive area of subkha in the center, some of which is saturated, with the ground water level at or just below the surface. Around the perimeter is a band of coarse shell sand rising one to three meters above high water level with occasional outcrops, as at the north west corner, of layers of rocky sandstone. Shallow inlets are present at the northeast and southwest corners of the island, and at the eastern end of the major bay on the south side, and in these areas and at the northwest tip, there are extensive stands of mangroves.



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History and Archaeology

Lying to the north of the major Khor al Bazm channel that divides the mainland of Abu Dhabi Emirate from a chain of offshore islands, Merawah has been used by local fishermen for at least several centuries.

Besides the recent buildings constructed for Sheikh Mohammed bin Zayed at the south east corner of the island, there are three small centers of population; on the western tip overlooking the narrow channel dividing Merawah from the island of Al Fiyah, the village of Liffah, in the center of the long bay on the southern side the village of Ghurbah, and in the center of the bay on the eastern end of the island, a smaller settlement (name unknown). In each case, the buildings are wooden shacks, apparently constructed, at least in part, from the ample supplies of driftwood to be found along the island's shores. None of these are permanent constructions. The surroundings of the village of Ghurbah, and of the unnamed settlement on the east of the island, were examined for surface evidence of earlier occupation.

At the western end of Ghurbah, several small shell mounds were identified, rising to a meter or so above the surrounding land surface. The surface of one mound was examined and yielded typical local shells (murex, oyster species etc.) as well as bones of turtles and dugongs. There was no evidence of charcoal or ashes in the mound, and there were only a few pottery sherds, all apparently of relatively recent date.

Around 200 meters north of the small settlement on the eastern side of the island, and approximately 25 meters inshore from the high tide line, marked by the innermost extent of the mangrove trees, was a larger shell mound, around 1.5 meters in height, and perhaps three meters across.

Besides the shells on the surface, intermixed with modern detritus like broken glass, there was a substantial scatter of pottery, most of which was probably of recent date. There was evidence from a discoloration of the sand on the surface and sides of the mound of fires having been built, perhaps for the smoking of fish and shellfish. The larger side of the mound, compared to those at Ghurbah, suggested that it might be older than the others. A small collection of the pottery on the surface was collected and sent to the Department of Antiquities and Tourism at Al Ain for examination.

On the north side of the island, adjacent to the track leading to the village of Liffah, and a few hundred meters from the village, a rectangular unroofed stone structure was noticed, with its walls standing around a meter high. There was a doorway facing east, and in the opposite wall another gap with stones in the form of a mihrab facing west (roughly in the direction of the holy city of Mecca).

The team was advised by a driver accompanying them (Darwish, a long-term island resident) that the structure was the remains of a mosque "perhaps 60 or 70 years old." This building was the only old permanent structure noticed during the survey. The surrounding area was not examined in detail, but may contain remains of some other dwellings.

Comments
  1. The residents of the island should be instructed not to damage the "mosque" in any way. It might be advisable to get an architect to examine the building, to see what needs to be done to preserve it in its present state.
  2. The Department of Antiquities and Tourism in Al Ain should be asked to send an archaeologist to the island to examine the "mosque" and the surrounding area and also to take soundings of the large shell mound on the east side of the island. There may also be graves on the island, near the fishing villages and known to the inhabitants, which should be preserved.
  3. The scanty natural resources of the island, and the fact that it is largely subkha, make it probable that there is little else of historical or archaeological interest. The areas around the existing fishing villages, however, may be worth examining more closely. (On the headland of Ras al Aysh, on the mainland opposite Merawah, graves and other evidence of occupation from the 3rd millennium BC have been located, indicating the presence of human settlement in the area. The depth of the Khor al Bazm, however, may have prevented access to Merawah, which, in any case, is very low-lying and has an inhospitable environment for human occupation.)
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Mammals

Feral Cat

One small skull was found on the southern part of the island, not far from the well. The habitat is not the type for true desert cats, so it is assumed that the skull was that of a feral cat of domestic origin, brought in by fishermen.

House Mouse (Mus musculus)

In several places, there were small footprints and round holes about three centimeters in diameter. No animals were seen but the small holes suggest that they are house mice, probably introduced many years ago from the fishing boats. The species is very adaptable and may have been able to adapt to living away from human habitation. They feed on dead fish, crabs and even on newly hatched turtles as they make their way down to the sea, as well as on plant seeds (Arabic 'far').

Hare (Lepus capensis)

We were informed that three hares had been released on the island a short time ago, although none were seen. Some small droppings were noticed, which were originally thought to be of this species or of young goats. On the mainland, hares are normally found in areas where there is plenty of grass, but other plants may also be eaten (Arabic: 'arnab').

Sea Cow/Dugong (Dugong dugong)

One skull and several rib bones from this species were found on the island's beaches.

The Khor al Bazm is well known for its large herds of dugongs, which graze on the sea grasses. A very large sea mammal, which never comes ashore, the dugong is now very rare in other locations in the Gulf and at one time during the Iran-Iraq War, they were believed to be extinct. A herd of around 600 animals of all ages was subsequently located between Qatar and Bahrain.

Rarely reported since, dugongs still survive in the Khor al Bazm and a few specimens are caught by fishermen every year, sometimes making their way to the fish souq in Abu Dhabi. The animal is the subject of a protection order issued by the Ministry of Agriculture and Fishery Resources.

J.N.B. Brown

Comments
  1. If, as is suggested, there are a number of feral cats on the island, consideration should be given to a possible reduction of their numbers. With little food available on the island, the cats may be having a serious effect upon the success of the few species of birds breeding there.
  2. Some specimens of mice should be trapped for scientific identification. Some other small mammals, like jerboas, may be present. The ENHG has suitable mammal traps for this purpose.
  3. Care should be taken, if possible, to prevent other species of mammals, like rats, being accidentally introduced on to the island. Great care should also be taken over the introduction of hares. With only a little natural food for them available, they could do serious damage to the natural vegetation.
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Insects

A small collection of insects was made, comprising beetles, flies, bees, wasps and butterflies. All except the butterflies are thus far unidentified; details will be supplied later.

Butterflies
Plain Tiger (Daunus chrysippus)

A large brown, black and white butterfly that breeds in the UAE and is quite common. It migrates long distances, so the one specimen seen during the survey may not have been resident. None of the plants known to be used as food for the larvae was seen on the island.

Painted Lady (Vanessa cardui)

Another migratory butterfly that occasionally travels in huge swarms across Arabia. No larval food plants were seen, so it probably does not breed on the island.

Desert White (Pontia glauconoma)

Very common in some years in all parts of the UAE, from the desert to the mountains. Only one specimen was seen. The larva of the species could feed on the available grasses.

Grass Jewel (Freyeria trochylus)

The smallest butterfly in the Arabian Peninsula, the larva of this species feeds on Heliotropium sp., so plenty of food is locally available.

Moths
Jujube Lappet (Streblote siva)

One larva believed to be of this species was found feeding on Crotalaria aegyptiaca, a tall shrub growing in the area of the fresh water run off. It also feeds on mangrove trees. The larva was not collected.

J.N.B. Brown

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Reptiles

The presence of five species of lizards, possible two species of snake and one species of turtle was established on the island. As many reptiles are nocturnal, it is probably that there are still more species to be found. However, the habitat is such that the numbers of each species is probably very small, particularly of the larger ones. No sea snakes were seen. These usually prefer rocky areas and coral reefs.

All the reptiles seen were harmless, with the exception of one that may have been a viper species.

Species List

Number Common Name Latin name Notes
1042 Green Turtle (Chelonia mydas) Only empty carapaces used as salt containers by fishermen and a few bones were seen on the island. It is possible that there are some nesting on the island, but the surrounding waters may be too shallow.

All species of turtle are subject to protection orders from the Ministry of Agriculture and Fisheries.
1260 Spiny Tailed Lizard (Uromastix microlepis) (Arabic 'dhub') One medium-sized 'dhub' was seen sunning itself along the central sandstone ridge. The species eats mainly grass and some insects.
1303 Stone Gecko (Bunopus tuberculatus) A small nocturnal ground gecko found under debris close to the shoreline, it feeds on insects and grows up to 12 cm.
1340 Dwarf Rock Gecko (Pristurus ruperstris) Seen on the gravelly area at the northwestern top of the island, this very small lizard is active during the day and moves quite fast over stones and rocks. It eats small ants and other insects and grows up to 7 cm.
1472 Short-nosed Desert Lizard (Mesaline brevirostris) Found on sandy desert areas close to the shoreline in the daytime. Feeds on small insects.
1502 Desert Monitor (Varanus grisceus) (Arabic 'wirral') Tracks of a large lizard with long clawed toes were seen in the sand at the base of the rocky outcrop at the southwest corner of the island and were almost certainly of this species. This lizard feeds mainly on small dead animals and is thus a useful creature. It moves around in daylight but avoids humans. It has very strong claws for digging in the ground and grows up to 80 cm.
1660 Cliff Racer (Coluber rhoderhachis) This snake has recently been found on the island of Sir Bani Yas although it is normally seen in mountain wadis. Undulating tracks of a colubrid snake were seen below the rocky outcrop at the southwestern corner of the island that could have been made by this species. It has no fangs and no venom and grows to 130 cm. Apart from the Sir Bani Yas specimen and the suspected presence on Merawah, snakes of the colubrid family have not been recorded by the Group on any of the UAE's offshore islands.
1815 Saw-scaled Viper (Echis carinatus) One snake seen resting in a 'dhub' hole may have been of this species but it moved quickly and was not clearly seen. It was a long way from the inhabited areas. The species has previously been found on an island at Ras Ghanada. Although shy and generally trying to avoid humans, this species, when threatened, makes a loud hissing noise by rubbing its scales together. It is nocturnal and hunts rodents and other reptiles; it grows to a length of 60 cm. It bites and can inject vasculotoxic venom.
J.N.B. Brown

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Flora

All the plants collected on the island were of the salt-tolerant species, from several different families. The annual plants, which grown after the first rains, had all died off and a collection of these will need to be made on a subsequent visit.

The island has a good coverage of plants except in the areas of true subkha, mainly in the center of the island where nothing will grown until there is a light covering of sand on it. However, only the mangrove trees grown more than one meter high.

There are several large stands of mangroves around the coastline, all of which appear to be in a very healthy state. There was no sign of oil pollution, with the exception of a few tar balls in sandy areas. Close to the Guest House of Sheikh Mohammed bin Zayed, there are a number of dead mangrove trees in a small inlet towards the airstrip. The cause of death is not known but could be due to bacterial or fungal infection or, more likely, to an accumulation of sedimentation (silt) over the pneumatophores (breathing roots). Mangroves are land-reclaimers, dying on the island side and spreading outwards towards the sea.

In some areas, particularly near the northwestern tip of the island, some trees on the landward side growing at or around the extreme high tide mark appear healthy. The area is not suitable for any large-scale tree planting as the fresh water supply is probably limited and relies on seasonal replenishment.

A hundred meters northwest of the fishing settlement of Ghurbah, there is a small freshwater catchment area where the vegetation is richer and more varied. A low ridge of sandstone rocks passes close by and provides a habitat for various kinds of plants, animals and reptiles. There is a shallow well containing brackish water and enclosed by a bund at the western end of this catchment area. It is used by local residents who have recently planted a few palm trees.

There are a few plants that would feed large introduced hers of animals. Only a few clumps of one species of grass were seen and these are probably the main food source of the Spiny-tailed Agamid (dhub).

A list of the plants seen and identified follows. One grass and one plant have yet to be identified.

Plant Species
Sphaerocoma aucheri
Arthrocnemum macrostrachyum
Anabasis setifera
Halcnemum strobilaceum
Halopeplis perfoliata
Salsola baryosma
Seidlitzia rosmarinus
Suaeda vermiculata
Crotalaria aegyptiaca
Lotus garcinii
Zygophyllum hamiense
Zygophyllum simplex
Helianthemum lippi
Limonium axillare
Heliotropium kotschyi
Avicennia marina
Cistanche tubulosa
Phoenix dactilifera
+ unidentified plant sp



Grasses/sedges
Cyperus conglomerates
+ unidentified grass sp.

Comments

1. Mangroves

As mentioned above, some of the mangrove trees at the southwestern corner of the island, near the runway, are dead. During the course of an Ecological Survey carried out in 1984 by J.M. Baker, of the Field Studies Council of the UK, and J.N.B. 'Bish' Brown, then of ADMA-OPCO, for the Abu Dhabi Company for Onshore Oil Operations, ADCO, dead trees were located in the same area. They had apparently been dead for some time, pre-dating the oil spill that was the reason for the survey. Some mangrove leaves collected from one tree at the time were found to be affected by a black fungus. This was identified by the Commonwealth Mycological Institute as being a fungus of Hyphomycete type, though identification as to genus and species was not possible. A further collection of specimens could be made, and culture work would be necessary to identify it more precisely and to elucidate possible effects on tree health.

The senior Environmental Protection Officer of ADCO visited Merawah on May 15 1990 during the course of a continuing annual survey of mangroves on the island and visited the mangroves near the runway. He had advised us that no signs of oil pollution were detected and that the trees were healthy.

2. In general, it should be stressed that the habitats present on the island are limited and very fragile, in particular in the area of the freshwater run off. There are insufficient natural supplies of fresh water for the planting of trees on any scale.

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The Beach and Shells

The north and east coasts are characterized by large amounts of detritus washed up on the beach and extending some way inland in low lying areas, presumably the result of the occasional exceptionally high tide. Among this detritus, much of which is driftwood, the skulls of a Dugong and Bottle-nosed Dolphin were found, as well as numerous shells.

Horn Shells (Centhidea cingulata) were numerous on the south coast of the island where they were the main constituents of the sand. Also common were Top Shells (Trochus erythraeus), Bubble Shells (Bullaria ampulla), and Worm Shells (Vermetus sulcatus).

Near the fishing villages, the shell mounds yielded substantial quantities of larger shells, notably from the Muricidae and various Oysters.

Species List
Gastropods    
Family Common Name Species
Patellidae True Limpets Patella exusta pica
Turbinidae Turban Shells Turbo coronatus
Trochidae Top Shells Trochus erythraeus
Minola gradata
Turritellidae Turret Shells Turritella cochlea
Vermitidae Worm Shells Vermetus sulcatus
Potamididae Horn Shells Cerithidea ungulata
Chicoreus ramosus
Hexaplex kuesterianus
Murex scolapax
Bullidae Bubble Shells Bullaria ampulla



Bi-valves    
Family Common Name Species
Mytilidae Mussels ? sp
Pteriidae Pearl Oysters Pinctada radiata
Spondylidae Spiny Oysters Spondulus exilis
Cardiidae Cockles Trachycardium lacunosum
Veneridae Venus Clams Cercenita callipyga
E.A. Pitt
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Birds

The island of Merawah lies within Map Square TA 25 of the Atlas of Breeding Birds of Arabia (ABBA) project, which also includes the island of Bazm al Gharbi, Al Fiyah and Junaina, and a stretch of coastline extending roughly from Mirfa to Thumayriyah. Details of the birds seen during the survey will be provided to ABBA and in several cases represent an extension of the previously known or suspected breeding range.

Habitats

Five distinct, though small, inhabitants were identified:

Subkha flats

This is a particularly harsh environment and the only resident species appears to be the Hoopoe Lark found in reasonable numbers throughout the island, especially in this habitat type and the coastal saltbush.

Although no nests were found, it appears likely that a few pairs of Saunder's Little Tern attempt to breed on the flats. Birds were observed carrying food, generally associated with mating behavior, but there did not appear to be any site preference shown. Odd pairs of terns of species were found all over the central section of the island.

The only other species to be found here was Kentish Plover. Breeding is probable but no evidence of chicks or nests was found on the flats.

Perimeter Shell Sand

The vegetation of this zone is little different from that immediately surrounding the subkha areas, with saltbush predominating. Hoopoe Lark and Kentish Plover are assumed to breed, but the only evidence of Kentish Plover breeding on the island during the survey was a bird giving a full distraction display in the northwest section. It appears that at the western end of the island, this habitat type may support an overspill small population of Black-crowned Finch Larks.

Central Sandstone Ridge

The vegetation along this ridge shows the only variation from the saltbush pattern of the rest of the island. It appears that this habitat is the center of the Black-crowned Finch Lark population, but numbers are low, with perhaps three or four pairs being involved.

Mangroves

The stands of mangroves are obviously the main attraction for the bird life of the island. As well as attracting migrants, they hold breeding species and act as roosting sites. All of the larger stands had singing Clamorous Reed Warblers. From the number of singing birds, the island's population of the species is probably between 15 to 20 pairs. The eastern side of the island also has breeding Graceful Warblers on the landward side of the mangroves, probably five or six pairs.

Herons of two species, the Western Reef and Little Green, were identified as roosting in the mangroves. It is likely that both species breed, although little supporting evidence was found. A platform was found in the southeastern mangroves but was considered not to be related to this year's nesting activity. Bird movements suggest that the mangroves in the southwestern corner are the most likely place for breeding of the Western Reef Heron.

Mudflats

Although the visit was made outside of the migration period, a surprising number and variety of waders were found to be using the extensive mudflats, especially on the northeastern corner of the island. See species list for details. The fish traps near the three fishing communities on the island were an attraction to both Herons and Terns, while the village waste tips and their insect life attracted migrants to breed. The 'artificial' vegetation around the Rest House of Sheikh Mohammed was found to contain one migrant species.

Species List

Number Common Name Latin name Notes
0081 Socotra Cormorant (Phalacrocorax nigrogularis) Resident breeder on neighboring island? Individual birds, both adults and juveniles, seen on the edges of the mudflats both days.
0107 Little Green Heron (Butorides striatus) Resident/breeder? Seen singly in and around mangrove trees on the northwest and southeast corners of the island. No evidence found, but a potential breeder on Merawah.
0118 Western Reef Heron (Egretta gularis) Resident/breeder? Commonest heron on the island. Maximum 18 northwest of the island. Nesting likely in southwest mangroves.
0147 Greater Flamingo (Phoenicopterus ruber) Migrant. One juvenile in northeast of island (31/05).
0301 Osprey (Pandion haliaetus) Resident/breeder? At least two seen on all coasts (31/05 and 01/06). No nest seen.
0450 Oystercatcher (Haematopus ostralegus) Winter visitor/migrant. Four seen on northeast of island (31/05).
0458 Crab Plover (Dromas ardeola) Resident. Maximum 45 in northeast of island (31/05). Small flocks of this species encountered along the north coast of the island. No evidence of breeding, but these birds may represent overspill from recently discovered colonies on Abu al Abyad.
0477 Kentish Plover (Charadrius alexandrinus) Resident breeder. The mudflats support a large population of this species. All evidence points to them breeding in reasonable numbers, although neither nests nor young were found. A bird giving full distraction display was found on the northwest of the island.
0478 Lesser Sand Plover (Charadrius mongolus) Winter visitor/migrant. Found on most coasts, maximum around 20 together northeast of island (31/05).
0486 Gray Plover (Pluvialis squatarola) Winter visitor/migrant. Found mainly on north coast, maximum four northeast of island (31/05).
0509 Curlew Sandpiper (Calidris ferruginea) Migrant. Two in summer plumage on northeast of island (31/05)
0512 Dunlin (Calidris alpina) Migrant. Two in summer plumage on northeast of island.
0519 Common Snipe (Gallinago gallinago) Migrant. One on southeast of island (31/05).
0534 Bar-tailed Godwit (Limosa lapponica) Winter visitor/migrant. Found on all coasts in parties of five to ten birds.
0538 Whimbrel (Numenius phaeopus) Migrant. One found on northwest of island (01/06).
0541 Curlew (Numenius arquata) Winter visitor/migrant. Found on all coasts, either singly or couples.
0546 Redshank (Tringa totanus) Winter visitor/migrant. Found on north coast with maximum of about 25 on northeast of island (31/05).
0548 Greenshank (Tringa nubularia) Winter visitor/migrant. Found on north coast with maximum of about 30 on northeast of island (31/05).
0555 Terek Sandpiper (Xenus cinereous) Migrant. Two found on inlet pools in southwest of island (01/06).
0585 Slender-billed Gull (Larus genei) Resident? One juvenile on northeast of island (31/05), two adults on northwest of island (01/06).
0606 Caspian Tern (Sterna caspia) Resident? Maximum of 21 on northwest of island at fish trap. Two showed barring on scapulars typical of young birds (first summer). Singles seen on most coasts (31/05 and 01/06).
0620 White-cheeked Tern (Sterna repressa) Migrant breeder to neighboring islands. Around 150 seen from the boat on way to island (31/05). Seen in ones and twos along the coast.
0622 Bridled Tern (Sterna anaethetus) Migrant breeder to neighboring islands. One seen on boat trip to island (31/05). Four seen over mudflats on southeast of island (01/06).
0625 Saunder's Little Tern (Sterna saunders) Migrant breeder. Maximum of 14 seen on northwest of island (01/06), pairs in the center of the island (31/05 and 01/06).
---- Feral Pigeon (Columba livia) Resident? Four or five birds seen around Ghurbah (31/05 and 01/06).
0690 Palm Dove (Streptopelia senegalensis) Resident/breeder? Present around areas of human habitation (31/05 and 01/06).
0953 Black-crowned Finch Lark (Eremopterix nigriceps) Resident breeder. Three or four pairs on territory on the central ridge in west of island.
0958 Hoopoe Lark (Alaemon alaudipes) Resident breeder. Commonest breeding bird on the subkha flats and perimeter shell sand.
0992 Swallow (Hirundo rustica) Migrant. One seen in southeast of island (31/05).
1122 Redstart (Phoenicurus phoenicurus) Migrant. Two male birds seen on northwest of island, one female on northeast of island near fish carcasses (31/05).
1137 Whinchat (Saxicola rubetra) Migrant. One male in mangroves northwest of island (31/05).
1144 Isabelline Wheatear (Oenanthe isabelliana) Migrant. One on mudflats southeast of island (31/05).
1227 Graceful Warbler (Prinia gracilis) Resident breeder. Five or six pairs seen on the landward side of the mangroves.
1252 Clamorous Reed Warbler (Acrocephalus stentoreus) Resident breeder. Fifteen to 20 pairs appear to be breeding in the mangroves around the island, from a count of the singing birds.
1312 Willow Warbler (Phylloscopus trochylus) Migrant, found singly in mangroves in most parts of the island (31/05 and 01/06).
1335 Spotted Flycatcher (Muscicapa striata) Migrant. One seen by fishing village on east side of island (31/05).
1508 Golden Oriole (Oriolus oriolus) Migrant. One female seen on southwest of island (01/06).
1519 Lesser Gray Shrike (Lanius minor) Migrant. One adult seen on southeast of island (01/06).
1866 Ortolan Bunting (Emberiza hortulana) Migrant. One female seen on southeast of island (31/05 and 01/06).
M. Pitt

Comments

  1. The numbers above are based upon the systematic List of Recent Holarctic Bird Species, produced by Professor K. Voous and published by the British Ornithologists Union (1980), as amended for the EURRING scheme. Status is for the UAE as a whole.
  2. No House Sparrows (Passer domesticus) were seen during the survey. The species has been spreading rapidly through the villages and towns of Abu Dhabi's Western Region.
  3. The Species List above should be viewed as merely an Interim List. Further studies on the island, particularly during the height of the spring and autumn migration, can be expected to yield a substantial number of additional species.
  4. The paucity of habitat on the island naturally affects the bird life. The introduction of artificially watered gardens and other vegetation in the area in the southeast around the Guest House and the runway could encourage more migrant species to stay to feed, rather than simply to stop over to rest.
  5. Because of the nature of the habitation of the island, only a restricted number of species of birds can be expected to breed on Merawah. It is not known whether species of tern, other than the Saunder's Little Tern, breed or have bred on Merawah, although they breed on neighboring islands. If an area of the island was set aside as a reserve (for example, the northeast corner, including the mangroves), more species might attempt to breed. If such a course is adopted, disturbance from local inhabitants and the population of feral cats should be prevented.
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Geology

Merawah Island is situated about 8 km northwest of Junaina Island and some 15 km north of the coastline. The island is characterized by an angular outline and is elongated in an easterly-westerly direction with 11 km of maximum length and 4 km in width. The island is located in the northwestern Abu Dhabi shallow marine areas, with water depth of less than two meters around the island.

The sea floor sediments around the island are made of carbonates.

1. Subkha deposit

Subkha deposits cover mainly the eastern part of the island with local patches on the north and southwestern areas. These deposits consist of clean sand grading into calcareous and gypsiferous silt, becoming haliferous near the coast with local halite crusts on the surface. Low lying areas locally include calcareous sandstone grading into gravel plains with eolian cover in places.

2. Desert Plain Deposit

Mainly localized in the northern and western parts of the island with limited occurrence in the southern part. These sediments consist of coarse gravel and sand/silt covering the low lying flats and the gently undulating surface with local isolated sand dunes.

3. Beach Deposits

The beach sediments cover the area between the subkha and the desert plain, mostly in the western part of the island. The sediments consist of carbonate sand and gravel, coastal dune and sand beach ridge marginal or adjacent to the present shoreline.

Besides the above-mentioned sediments, the following deposits also occur in restricted patches:

a) Tidal Flats and Marshes

These deposits are present at coastal areas and are made up of carbonate sand and silt.

b) Calcareous Sandstone

The calcareous sandstones occur locally in the southwestern and northeastern areas of the island and consist of porous calcareous sandstone.

Comments

The above descriptions summarize the published state of knowledge on the island. Structurally, it falls on the western flank of a major dome, focused on Hail Island. The latter formed as a consequence of Cambrian salt movement at considerable depth (20,000 feet +) and the island must overlie a localized deep salt pillow. Unlike Sir Bani Yas or Jebel Dhanna, this salt has not pierced to the surface. However, close examination of large-scale satellite imagery clearly indicates the presence of solid rock outcrops to the east of Merawah, with a configuration suggestive of a surface anticline.

More importantly, if red sand stones are present on the island, then it is a reasonable speculation that deposits of Miocene Age could be present, comparable to the Bainuna Formation at Jebel Dhanna. These are the sediments in which major fossil vertebrate finds have been made. This would tie in well with known surface outcrops of this formation along the mainland coast directly to the south. If this speculation is confirmed, and these beds are in structural configuration, it would imply that the emergence of Merawah is a very recent geological phenomenon indeed.

T.D. Adams

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Conclusion

The two-day survey of the island produced a number of interesting results although much more remains to be discovered during any subsequent surveys.

Taking into consideration the restricted and highly specialized habitats available, the wildlife (birds, reptiles etc.) is of some interest, with, in the case of the reptiles, some species being present or probably present, such as the Colubrid snake and the Desert Monitor and Spiny-tailed Agamid, which are unlikely to have been introduced by human agency. They must, therefore, have been present on the island before it became separated from the mainland over 8,000 years ago.

These species are likely to have survived only because of the limited human impact upon the environment in the millennia that followed. Any planned development on the island should, therefore, take into account the fragility of the local environment.

 


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