Introduction - Drainage Basins - Makran
The Makran is the coastal region of southeastern Iran between the Straits of Hormuz and the Pakistan border. In the west of this region the relief runs in a north-south direction parallel to the coast but from Jask eastwards the relief runs west-east, again paralleling the coast, to the Pakistan border. The rivers and streams of the Makran all drain to the sea at the Straits of Hormuz and the Sea of Oman. The inland Hamun-e Jaz Murian basin is isolated by mountain ranges reaching peaks in excess of 2000 m. The coastal drainages are often incised and the larger watercourses pass through tangs over 1000 m deep (Harrison, 1968).
I have not seen the watercourses between Jask and the upper Geh (= Nikshahr, Kaeyr or Kalar) River drainage (mouth is at 25°37'N, 60°08'E) but descriptions by Harrison (1941) indicate they are similar to other areas of Makran. It seems probable that only the Minab and Sarbaz Rivers have, or nearly have, a perennial and continuous flow along most of their course. Even these rivers are quite shallow and the Sarbaz in particular is easily fordable on foot along its entire length (ca. 280 km). The Minab River flows over a shorter course (ca. 220 km) than the Sarbaz, but has a greater flow regime. At Minab (27°09'N, 57°05'E) and at Rudan (27°26'N, 57°12'E) the Minab River was up to 100 m wide with an estimated maximum depth in pools of 2-3 m. The lower Sarbaz River was a series of shallow, muddy pools in the bottom of a canyon with some water flowing over sills connecting the pools (in early December 1977). The lower Sarbaz has been designated a Wetland of International Importance. In its middle and upper course the Sarbaz varied from a very shallow and narrow stream connecting pools (some of which were fishless) to what must be termed a river in the semi-desert environment of Baluchestan, with a width of 10 m, a depth of about 1 m and fast current. The rockfill embankment Pishin Dam built over the rivers Pishin and Sarbaz is 63 m high, has a crest length of 400 m and can store 175 million cu m of flood waters (http://netiran.com/news/IRNA/html/930418IRGG10.html).
The other streams of the Makran have little running water, often become isolated pools a kilometre or more apart, and regularly dry up along much of their length. Several rivers between the Mazavi (= Geru) River (mouth is at 26°56'N, 56°56'E) and the port of Jask are named and marked prominently on maps, but these were all dry in their lower reaches in late November 1976. Some flow in their upper reaches is to be expected, but its extent will depend on topography and recent climatic conditions. A dam and irrigation network is to be constructed on the Jaghin River east of Jask (IRNA, 26 June 2000).
Coad (1997a) combined the basins of the Makran, Lut, Jaz Murian, Mashkel and the Pakistani Pishin Lora as a single entity, expanding on earlier work by Mirza (1980). Mirza proposed the name Gedrosia for the Baluchistan Plateau west of the Central Brahui and Hala Ranges in Pakistan. The easternmost river along the Makran coast is the Hingol in Pakistan. East of this river the fauna becomes much more diverse at all taxonomic levels and the fauna is an Indus River one. In the north, the Pishin Lora River basin lies partly in Pakistan and partly in Afghanistan. Beyond this basin to the north and northwest lies the Registan Desert and then the Sistan basin, with its distinctive faunal mix including schizothoracines (Schizothorax, Schizocypris and Schizopygopsis) and a crested loach (Nemacheilus rhadineus). To the northeast lies an area designated as Yaghistan by Mirza (1980), with its unique faunal association. The westernmost river is the Dasht, whose upper reaches cross the Iranian border. The western limit of Gedrosia is the Mashkel River basin which has several tributaries from Iran. Coad (1997a) proposed that the limits of Gedrosia be extended westwards to encompass the Iranian part of the Mashkel basin, along coastal Makran as far west as the Minab River, and internally to include the Jaz Murian and southern Lut basins. West of the Minab River, the fauna was deemed to be unique in having an endemic cichlid, Iranocichla hormuzensis and in having members of such Euro-Mediterranean and Southwest Asian (= Middle East) cyprinid genera as Barbus, Chalcalburnus (= Alburnus), Leuciscus (= Squalius) and the cobitid genus Cobitis not found further east. However specimens of Iranocichla hormuzensis have been collected from the Minab River by H. R. Esmaeili (examined by me in 1997) and this river may properly belong to the Hormozgan basin. I did not collect this species in the 1970s and it is possible that the record is an introduction since that time from adjacent rivers as there have been many accidental movements of fishes in Iran associated with fish farming.
Generally basins within Gedrosia appear most closely related to their geographical neighbours and support the argument for containing these endorheic basins in one division. No basins are strongly and uniquely linked although Makran and Jaz Murian uniquely share Garra persica and Channa gachua, and Mashkel and Makran uniquely share Aspidoparia morar and Nemacheilus baluchiorum.
At the species level Gedrosia is most closely related to the adjacent Yaghistan and Indus basins to the east, then to the adjacent Sistan and Hormozgan basins, and least of all to the remoter Tigris-Euphrates basin. Its principal relationships are eastern, to some extent northern and very little to the west.
The generic pattern is different from the species one. The Sistan basin has the highest share of genera, followed by Yaghistan and Hormozgan. The Indus and Tigris-Euphrates share far fewer genera but they have a greater diversity (5.8 and 2.3 times that of Gedrosia). It is therefore not surprising that Gedrosia shares proportionately more genera with immediately neighbouring basins whose fauna at the generic level is also limited. However, omitting genera found in all basins or unique to a single basin, reveals that Yaghistan and Indus share 5 of 7 such genera exclusively with Gedrosia. Only Capoeta shows a different pattern being found in the western basins but not Yaghistan and Indus. The last genus is Crossocheilus which is found in the Indus, Yaghistan and Sistan basins. Therefore, generic level comparisons also show that Gedrosia is most closely related to the east.
The transitional nature of Gedrosia is evidenced by its having the distributional limits of certain wide-ranging species. This is most notable for species reaching their westernmost limits, namely Aspidoparia morar, Crossocheilus latius, Channa gachua, Labeo dero, Puntius sophore, and Tor putitora (the last three not recorded from Iran). Species are probably limited by environmental conditions such as temperature in comparison with the warm waters of South Asia. However a significant factor, as recognised by local people, must be the poor physical condition of Baluchistan. Freshwater marshes, lakes and large rivers are all absent. Desiccation of water bodies is common and many streams are intermittent. Habitat diversity for fishes is severely limited. All the common fish species are non-predatory - most fishes feed on small insects or scrape aufwuchs from the rocky stream beds.
In contrast to western limits, only one species has a distribution which is principally Southwest Asian and reaches its eastern limit in Gedrosia, namely Capoeta damascina. The remaining species have distributions which are centred on Gedrosia and immediately adjacent basins. There is also a link northwards in that some species have an extensive north-south distribution, namely Garra rossica, Nemacheilus kessleri and N. sargadensis.
One of the most interesting features of Gedrosia is its paucity of fishes. Diversity is low, presumably a result of the physical conditions noted above, compounded by desiccation and during climatic variations both past and present. Gedrosia is presumably an important former route of dispersal for taxa from South and Southeast Asia to Southwest Asia and beyond. The significant absences are of taxa found in the Tigris-Euphrates basin to the west and in the Indus basin to the east.
At the family level, five families are found both west and east, but not in, Gedrosia. These are Cobitidae, Bagridae, Siluridae, Sisoridae and Mastacembelidae. No cobitid or silurid genera are shared. They may be quite ancient and their absence from Gedrosia is by a vicariant event or their dispersal was via a northern route to the Tigris-Euphrates and separately to the Indus. The most significant absences are of such genera as Mystus in the Bagridae, Glyptothorax in the Sisoridae, Mastacembelus in the Mastacembelidae (Mastacembelus is not found in eastern Iran and hence does not have a continuous range throughout the Orient (pace Travers (1984)), and also Barilius in the Cyprinidae. The last three genera are found in drainages entering the upper Persian Gulf separate from the Tigris-Euphrates basin but probably had a recent connection with that basin during the Pleistocene lowering of sea levels when the Gulf was drained.
Berg (1940) suggested that fish dispersal across this region was facilitated by the coastal rivers of Iranian and Pakistani Baluchestan being part of a single river system in the Pliocene, since submerged by subsidence. This distribution of these genera is not, therefore, a remnant of the dispersal across Iran from Asia. It is possible that the Pleistocene fore-deep of the Himalayas had connections with the Tigris-Euphrates basin which extending down the Persian Gulf as a river valley. Hora (1937) and Menon (1957) refer to wet, marshy, tropical conditions and headwater captures along the whole southern face of the Himalayas and westwards during the Pliocene and early Pleistocene facilitating the spread of fishes from the east to what is now Southwest Asia (= Middle East) and Africa. However, it is here considered unlikely that the Tigris-Euphrates and Gedrosian rivers were once tributary to the Indus when sea levels were lower during glaciations as the Gulf of Oman descends to an abyssal plain at 3340 m as noted above. These taxa probably reached the Tigris-Euphrates basin across the Iranian land mass and subsequently became extinct as desiccation increased. Their absence from Gedrosia is probably by loss.
Hora (1937) and Briggs (1987) consider that cyprinids entered Africa from southeast Asia 18-16 MYA, in the early Miocene, while other groups moved through Iran and the Arabian Peninsula beginning in the early Eocene. Kosswig (1951; 1952; 1955a; 1955b) notes the similarity at the generic level between Indian and African fishes, e.g. the cyprinids Barilius, Garra and Labeo, indicating that these fishes arrived in Africa from India after the desiccation of the Syrian-Iranian Sea in the Pliocene. The primary route, according to Kosswig and to Por (1987), was a northern one around the barrier of the Persian Gulf and Sea of Oman via northern Arabia, Syria and the Levant. Cooling conditions in these areas, and presumably too in Gedrosia, during the Pliocene and especially the Pleistocene glaciations, and arid climates at times, were unsuitable for tropical forms.
Potential endemic taxa are Cyprinion milesi, N. bampurensis (in Iran), Labeo gedrosicus, Labeo macmahoni, Nemacheilus baluchiorum, and N. brahui (in Pakistan). The systematic position, as species, of Cyprinion milesi and Labeo gedrosicus need further study, and the distributions of the three Nemacheilus species are in contention. Endemism may be relatively high or low dependent on the resolution of these problems.
Fishes in the easternmost part of the basin have a unique predator to contend with among Iranian species. The gandoo (marsh crocodile or mugger, Crocodylus palustris) is found in the Sarbaz, Khaju and Bahu Kalat rivers including the Pishin Dam, makeshift lagoons and fish culture ponds. It is feeds on Cyprinus carpio and Periophthalmus (Crocodile Specialist Group Newsletter, IUCN, 18(1), WWW Edition, downloaded 16 December 1999 from www.flmnh.ufl.edu/natsci/herpetology/newsletter/news181b.htm; report by A. Mobaraki; A. Mobaraki, pers. comm., 2000). The Cyprinus carpio are escapees from fish farms.
© Brian W. Coad (www.briancoad.com)