Bulletin 42 - November 1990: The Natural History of Merawah Island
The Natural History of Merawah IslandEdited by Peter Hellyer
Table of ContentsIntroduction
Members of the team
The Island of Merawah
History and Archaeology
The Beach and Shells
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.Return to Table of Contents
Members of the team
The main participants in the two-day survey were as follows:J.N.B. (Bish) Brown
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).Return to Table of Contents
The Island of MerawahLocation
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.
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.
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
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
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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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.
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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
+ unidentified plant sp
+ unidentified grass sp.
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.
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.Return to Table of Contents
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
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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.
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.
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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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.
Patron: H.E. Sheikh Nahayan bin Mubarak Al Nahayan
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